Proceedings
of the
Symposium
on the
Current Status
of the
        problem
and its control...
Thursday, April 26, 1973
                          33 W. 42nd Street,
                          New York, N.Y.
                          Sponsored by

                          REGION II
                          MIDDLE ATLANTIC CONSORTIUM ON
                          AIR POLLUTION (MACAP)

                          Funded by
                          Manpower Development Office
                          Environmental Protection Agency
                          Symposium Chairman

                          Elmar R. Altwicker, Ph.D.
                          Bio-Envir. Engineering Division

                          Rensselaer Polytechnic Institute
                          Troy, N.Y. 12181
                          518- 270-6554

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      Proceedings of the

           Symposium
 on the Current Status of the
  NO  problem and its control
    x

  This Symposium was held on
   Thursday, April 26, 1973
     CUNY Graduate Center
       33 W. 42nd Street
      New York, New York
         Sponsored by

           REGION II
 MIDDLE ATLANTIC CONSORTIUM ON
         AIR POLLUTION
            (MACAP)

          Funded by
 Manpower Development Office
Environmental Protection Agency

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                            CONTENTS                                Pa§e
Introduction by Elmar R. Altwicker, Symposium Chairman               1


Current Understanding of NO -Formation in Mobile and Stationary      2
Combustion Sources by Irving Classman, Center for Environmental
Studies, Princeton University.


NO -Control and Problems in Mobile Sources by William Balgord,       27
  •y1
New York State Department of Environmental Conservation.


Technical and Economic Approaches of Power Plants towards NO^-       28
Control; Air Quality Benefits and Costs from Utility NO^-
Regulations by Peter C.  Freudenthal, Consolidated Edison Company
of New York.
Control of NO -Emissions from and Control Equipment for Stationary   47
Sources; Future Approaches to Stationary Source Control of Stack
Gas NO  by  Aaron J. Teller,  Teller Environmental Systems of New York.
      x  -


NO -Control by Wet Scrubbing  by Robert S. Kapner, Engineering       53
Division, Cooper Union of New York.
EPA-View of Stationary and Mobile NO -Source Control by Conrad      101
Simon, Air Programs Branch, Environmental Protection Agency of
New York.
                              ii

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Introduction

     This volume contains all but one of the papers that were presented at the

MACAP-symposium on NO -control.  The problem of NO -control seemed - and still is -
                     X                            Js.

timely and was chosen as the subject of the first MACAP-symposium.  In addition

to the technical information transmitted, this and future symposia are intended

to foster the interaction between control officials, industrial concerns, consul-

tants, and academicians on timely air pollution topics.

     Two important topics - atmospheric chemistry and health effects of NOX -

were purposely excluded from the symposium, in order to permit greater treatment

in depth of the control aspects.  It was therefore of considerable interest to the

chairman that the panel discussion - not included in these proceedings - elicited

a great deal of comment from the audience on standards and their relation to health

effects; another indicator of the breadth and complexity of the NO -problem.
                                                                  ^C

     The organization of this symposium was greatly simplified by the able assist-

ance of John Bove, Paul DeCicco, Carl W. Kreitzberg, and Gerald Palevsky.  All

but one contributor cooperated in making full length, referenced manuscripts

of their presentations available.
                                        Elmar R. Altwicker
                                        Symposium Chairman
                                        Rensselaer Polytechnic Institute
                                        Troy, New York  12181
                                         1.

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       CURR-EA'7 UNDERET/vl.uING OF NO  FORMATION   ^
     Tfi MOI3ILE AND STATIONARY COMBUSTION SOURCES

                         by
                                 2
                   Irvin Classman
          Center for Environmental Studies
       Princeton University, Princeton, N. J.

                  I. INTRODUCTION

         Current interest in predicting NO „ emissions  from
                                          jTi.

mobile and stationary sources has led to the formulation

of various kinetic models for the formation of nitric

oxide  (NO) in combustors.  The formation of nitrogen

 (NO-) from nitric oxide has received less attention;

however, there does appear to be general agreement as  to

the main kine tic step in this conversion; simply NO +  OH

-»• NO- + H.  There are two principal sources of nitric  oxide

in the combustion of conventional fuels:   (1) oxidation of

atmospheric  (molecular)  nitrogen and (2) oxidation of

nitrogen containing compounds in the fuel  (referred to as

fuel nitrogen).

         Although the major interest of concern here is

the kinetic routes for the formation of NO, of greatest

concern from a practical point of view is the  total NO
 The author's work in kinetics is supported by the Air
 Force Office of Scientific Research under Grand  69-1649
 and the Environmental Protection Agency under Grant R-801194
2
 Director and American Cyanamid Professor of Environmental
 Studies.

 This paper developed from the original framework given  in
 Reference 1.
                        2.

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emission from a particular device.  Lest one thinks

kinetics are the dominant factor, it is best to ini-

tially discuss the NO  emission problem in the context
                     X
of flames.


          II.  THE ROLE OF FLAME STRUCTURE

        If one premixes a gaseous fuel with air so that

the system is completely homogeneous and if the mixture

ratio falls within the flammable range, then given an

ignition source a flame will propagate through the

  • .u    4
mixture.

        It is possible to calculate from simple thermo-

dynamics the maximum temperature reached in such flames

when one assumes that the conditions approach adiabatic

ones.  Such calculations can be made with sufficient

precision such that the calculated adiabatic flame

temperature is very close to the flame temperature

measured experimentally.  l.ideec , one can readily cal-
4
 Under certain experimental conditions related to con-
 finement, the flame, a subsonic wave (deflagration), will
 undergo a series of transitions in which it will repeatedly
 become a detonation wave  (supersonic).   The temperatures
 and pressures generated by detonation waves are substan-
 tially higher than a deflagration wave (flame), the amounts
 of NO formed would be much greater as well.  However,
 detonations play no significant role in mobile and sta-
 tionary power plant combustion processes and will not be
 discussed further.
                         3.

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 culate  the adiabatic flame temperature as a function


 of  fuel/air ratio(2).  The variation, which is similar


 for all  fuels,  is shown on a relative basis in Figure 1,


 in  which the temperature is plotted as a function of <{>,


 the equivalence ratio.  The equivalence ratio is defined


 as  that  ratio of the actual fuel/air ratio to the value


 at  the  stoichiometric condition — the condition under


 which there is precisely enough oxygen to burn all the


 carbon atoms present to carbon dioxide and all the hydro-


 gen atoms present to water vapor.  Large values  of 


 correspond to a  (fuel) rich condition and small values to


 a  (fuel) lean condition.  As a very simple explanation,


 the temperature drops on the rich side because there is


 insufficient oxygen present to burn all the carbon (or


 carbon monoxide) and hydrogen to their fully oxidized


 states which gives the greatest energy release.  The


 drop on  the fuel lean side can be considered as a dilutive


 effect by the excess oxygen.



         At each temperature it is possible to calculate


 the equilibrium concentration of NO given by the equation






         II       1/2 N2 + 1/2 O  ^?NO






from the equilibrium concentration of formation, K  f
                                                  P r £ i
                        4.

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          K    =   PNO          _    XNO

           P'f        1/2    1/2        1/2     1/2

                  PN   P0         XN     X0
                   IN     U          N      U
where  p  is  the  partial  pressure  and x  is  the mole fraction


of  the component in the complete combustion system.  The


K   f is  readily found in thermodynamic  tables or calculated


as  a function of temperature  from the  relationship



                 AF°  =   -RT  In  K   .p
                               Pf f

where  AF° is the standard state  free energy charge of the

                                                 (2)
equilibrium reaction of formation written above.


         One should  not infer  from the  manner in which the


equilibrium reaction is written  that NO forms by the direct


reaction of N2  and  O~.   In  fact  as will be discussed in


detail later the route  is through oxygen atom attack on


the nitrogen molecule.


         Since  K  ,;  is  a function of temperature alone, it
                 P'T

is  not surprising that  the  equilibrium  concentration of


NO  formed in homogeneous premixed fuel/air flames would


be  expected to  peak  around  stoichiometric just as the


temperature does, provided  of  course that time be allowed


for equilibrium condition to prevail.


         It should be underscored  that  the utility of


making estimates  of  NO  formation  by an  equilibrium calculation
                          5.

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 exists  only  for  premixed gaseous fuel/air flames.  Most



 practical  combustion devices  (other than laboratory



 burners) utilize condensed phase fuels or gaseous fuel



 jets  under conditions which the fuel and air first mix



 and then burn.5  Flames which exist under such conditions



 are referred to  as diffusion flames because the rate of



 burning is controlled by rate of diffusion of fuel into



 air and vice-versa.  Figure 2a represents the situation.



 When  a  liquid droplet burns the flame created releases



 heat  which diffuses back to the fuel to evaporate it,



 then  the fuel diffuses towards the flame where it is con-



 sumed.  The  air  is similarly heated and oxygen diffuses



 towards the  flame where it is consumed.  Also shown in



Figure  2b  is the burning of a gaseous fuel jet.   In this



case  the shape and position (length) of the flame is governed



by the  fuel  injection rate; nevertheless, once the flame



exists,  fuel and oxygen diffuse towards the flame where



they are consumed.   What is so very important is the fact



that it has been well established that the fuel and oxi-


                                                           (3
dizer flow towards each other in stoichiometric proportion



and because the reaction rates in this case are so much



faster than the diffusion rates, the reactions are con-



sumed in a very narrow zone.   Since the flame is like a
* A large furnace injecting gaseous fuel or an aircraft

  gas turbine burning natural gases are specific examples.
                          6.

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sink for fuel and oxygen, it is not difficult to accept



intuitively that they approach each other at a ratio of



rates equal to the  stoichiometric index.  Thus in a drop-



let burning situation where it is possible to specify an



overall mixture, two temperature zones exist — one, a



zone around each droplet  (or group if they are close



together) and the other the final equilibrium temperature



corresponding to overall  fuel-air mixture ratio.  Thus



even though a system such as a diesel engine may have a



very lean fuel-air  ratio, it will produce more NO than



expected because each droplet burns so that the flame



around it corresponds to  the temperature at stoichiometric,



        The consideration of the character of the flame



is the major one when concerned with the NO  emissions.
         J                                 x


It is not surprising then that most research towards



reducin j NO  emissions in devices such as aircraft gas
           J^


turbines is directed toward prevarporizing the fuel and



premixing it with the air prior to injection into the com-



bustor can.




               III.  KINETIC ROUTES


                 (4)
        Zeldovich    was  the first to propose that the



mechanism of NO  formation can be represented by the



sequence of reactions
 The units of all specific reaction rate constants, k,

 values are cm, cal, °K, mole, sec.
                      7.

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                                        4
III.   0 + N9  •*>  NO + N      k=1.4x!0exp  -75800/RT
           £t




           2
     IV.   N +  02  -*  NO  + O      k=6.4x!04exp -6280/RT
 For any kinetic  calculation the reverse reactions, although



 not of  prime  importance,  should be taken into account.



 The specific  reaction rate constants, k, are taken from



 Reference  1.   The constants for the reverse reaction can



 be determined from these  and the respective equilibrium



 constants.



         There has .appeared to be general agreement that



 one could  predict NO formation in flames based on the



 Zeldovich  mechanism plus  the addition of the reaction




     V.  N +  OH   ->-    NO  4-  H   k=2.8x!013




 Since this reaction involves two reactive radicals whose



 steady  state  concentrations will always be very low, it



would not  normally be of  significance.  However,  emis-



sions standards in NO  have been set so low that it is
                     X


not wise to ignore the possible contribution from this



reaction.  Results from several analytical studies of



NO formation  in combustion processes have shown that



for most practical situations that radicals involving



N20 or NO  and the recombination





    VI.    N + O + M (third body) •>  NO + M
                         8.

-------
do not play a significant role in NO formation.


        Considering that Reaction III must be very slow,


most investigators believed that the major portion of NO


forms in the post flame zone of the combustion process.


This zone is that area which exists after the major


energy release reactions have been completed and physi-


cally corresponds to the area past the luminous flame zone.


In describing Bunsen burners it is usually referred to as


the burned zone -- that zone which 'has the very faint


dull red emission.


        The basis for this belief was reinforced by the


very interesting calcualtions of Martenay.    Some of his


typical results are shown in Figure 3.  The system he con-


sidered is in essence a constant temperature (and pressure)


flow system in which the fuel and air are considered to begin


reaction at some zero time.  At t=10  sec the system can be


considered to have the composition as given by the left


hand ordinate scale.  Thus the results would be applicable


to any fuel-air combustion which would have this initial

   _7
(10  sec)  composition.  What the curves in Figure 3 show


so very nicely is that all the constituents which relate


to energy release have formed quite rapidly and appear to


reach their equilibrium values by at most 2x10  sec.


However,  at this point the NO is less than one molar part
                        9.

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 per million.   Even  at  10  2sec, the right hand ordinate,




 the NO is a factor  of  10  less than its equilibrium value,




 which is specified  on  this ordinate as well.  Thus it




 would appear, from results such as these, possible to quench




 the combustion reaction in steady flow devices prior to




 NO formation  and still obtain maximum energy release.




 Indeed there  is a great deal of current development work




 whose objective is  to  establish this concept as a practical




 scheme.



         Perhaps it  would be wise to comment here on




 another  development effort to reduce NO  emissions.  This




 one concerns  the injection of water into the combustion




 zone.  The  addition of water has two effects -- one to




 reduce the  temperature and thus the oxygen radical .forma-




 tion  and  ratio  of Reaction I, and, two, to scavenge the



 oxygen atoms by the route





   VII.         O   +  H20   ->   2 OH





 Since hydroxyl  radicals (OH), for all intents and purposes,




do not react with molecular nitrogen to form NO, the




 scavenging could be effective.  It is quite apparent that




the first effect is most dominant.





                 IV. "PROMPT" NO




        In several recent NO formation studies, rates have
                       10 .

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been found to exceed that given by the post combustion


mechanism.      Experimental measurements of NO concen-


trations made in the post flame zone gave values which


when extrapolated back to the flame position indicated


concentrations of NO in the flame that would not be


considered negligible in the context described earlier


and rates larger than those extrapolated from the Zeldo-


vich mechanism in which the equilibrium values of oxygen-


atom concentrations were used.  Fenimore    referred to


the NO formed in the flame as "prompt" NO and concluded


that reactions other than Reactions III-IV must be taking


place.


        The question of whether the Zeldovich mechanism


and Reaction V completely accounts for the total NO forma-


tion from atmospheric nitrogen in combustion systems is


the major unsolved matter in thJs area.  This point will


be discussed in the subsequent paragraphs.


        To put the question in the proper context it is

                                                    (9)
best to discuss some related work.  Bowman and Serry


for example, studied nitric oxide formation during shock-


induced methane combustion.  The pressure and temperatures


created behind a shock give the gas a flow reactor character


in that reaction can be considered to take place at a


constant pressure in a constant temperature bath.  This
                       11.

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 Thus, it is argued that "prompt" NO comes about from a



 large oxygen radical concentration in the flame zone



 and that the intuitive concept that one could use equi-



 librium oxygen radical concentrations to gain an estimate




 of the initial NO formation is misleading.



         Actually it should be realized that Bowman has



 proven simply that the modified Zeldovich mechanism only



 suffices for shock induced combustion and that it does



 not appear necessary to include any other reactions.   This



 physical situation is different from flames in which there



 is a very definite exponential rise of temperature from



 the ambient condition to the flame temperature.   Further



 there are diffusion effects in flames which must be ac-



 counted  for in  making kinetic estimates.   Thus these



 calculations necessary to  make an exact analytical calcu-



 lations  of  the  kinetics in flames where species and



 energy diffusive  are  involved are much too  complex con-



 sidering  the number  (*<34)of specific   reaction steps'



 involved  in  the overall combustion process.




        Although  there  has been a tendency  to accept the



oxygen radical overshoot as an explanation  of the "prompt"



NO, recent work in Germany   '   '  substantiates some of



Fenimore's early  postulates and reopens the thinking with



respect to other  reactions --  particularly  in fuel  rich
                        12.

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situation is achieved by using methane and oxygen in a



large excess of argon as the initial mixture.  The con-



centration profiles measured were compared with detailed



kinetic calculations in which the time rates of change



of species concentrations and thermodynamic properties



during the reaction were determined by numerically inte-



grating the coupled reaction kinetics, state and energy



equations.  The experimental and analytical results are



depicted in Figure 4.  There are several interesting



and important observations to be made from this figure.



The initial rate of NO formation exceeds the rate later



in the reaction -- for both lean and rich mixture.  The



slope at any point in the curve is an indication of rate



of formation of NO.  However, the NO attains its equili-



brium value much more rapidly in rich mixtures than in



lean micutres.  But, most importantly, in regard to the



major r^int being discussed in this part of this paper,



the experimentally measured concentrations agree with



those of the analytical calculations. Bowman and Seery



used only Reactions III-IV in their analytical scheme




and Bowman,   in essence, has concluded that the prompt



NO could arise from the large overshoot of oxygen radical




concentration over its equilibrium which was found.  This



same overshoot is very graphically depicted in Figure 3.
                        13.

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 flames.  Just and his coworkers^14   '  made, extensive



 experimental determinations of NO formation in various



 hydrocarbon flames.  From these results they determined



 the "prompt" NO.  They show that for the hydrocarbon-air



 system the "prompt" NO increases with equivalence ratio,



 peaks at about an equivalence ratio of  1.4  and then



 drops off sharply.  Perhaps the most conclusive experi-



 ments of Just, et al.,     were those in which they



 controlled the temperature of. various propane-oxygen



 flames by adding nitrogen diluent.  They then plotted



 "prompt" NO as a function of temperature for various



 equivalence ratios.  These results are  shown in Figure 5



 taken from Just, et al.      In this figure  A is the equiva-



 lent ratio on  the basis  fuel to oxygen.   Just     makes



 one very interesting speculation from Figure 5 and these



 will be  reinterpreted by this  writer.   The  plots in



 Figure  5  seem  to indicate  that at low temperatures the



 slopes of  the  correlating  lines are small and that at



 high temperature  the  slopes  are large.   The change in



 slope is most clearly  seen  for X  = 1.1  and  1.2.   If one,




 as a first approximation,  interprets  the slope as an



 activation energy  (EA) or  being determined  by the E  of



a particular reaction, then  he can estimate that at low




temperatures EA = 12-16  kcal/mole  and at high temperatures
                       14.

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E  = 65 kcal/mole.  This later value is of the same order
 f\


of magnitude as that  for Reaction III.  The very interest-



ing speculative conclusion is that at high temperatures



the Zeldovich mechanism prevails and that at low tempera-



tures some other reaction mechanism is effected.  Further,



the actual stoichiometry is not of total significance,



but the specific temperature which prevails is.



        The German workers also measured HCN concentration



throughout their flames.  They found that the HCN concen-



tration varied as a function of equivalence ratio,  but



somewhat opposite to  that of the "prompt" NO.  The HCN



concentration remained    at low levels until the equiva-



lence ratio which "prompt" NO dropped off sharply,  then



the HCN concentration rose sharply.  They conclude that



the HCN is an intermediate in the formation of NO and



when whatever is oxidizing the HCN disappears, NO no



longer forms and the concentration of HCN rises sharply.



Fenimore  previously had postulated the possibility of



HCN formation in fuel rich flames from the step




   VIII.    CH + N9   ->-   HCN + H
                  £*



                 V.  FUEL NITROGEN



        Very little specific information exists on the



kinetics of formation of NO from fuel nitrogen.  The



existing data suggest that the conversion to NO from fuel
                      15.

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 nitrogen is very rapid and occurs  on a time  scale compara-
 ble to the combustion reaction.  This fact is significant
 in that it precludes the use of  quenching to prevent NO
 formation.  One simply could not get the  energy release
 and stop the NO formation.   The  effect of fuel nitrogen
 was dramaticallly demonstrated in  the early  experiments
 of Matin and Berkman.   '  They measured the NO emissions
 from an oil-fired laboratory furnace using a base oil.
 They repeated the experiment with  0.5% pyridine added to
 the base oil.   The pyridine additive increased the NO
 emissions by a factor  of  five.
          Various experiments in  which fuel nitrogen was
 introduced into flames by different  techniques show that
 the NO increases rapidly  to values significantly larger
 than its  equilibrium value  in the  flame zone and decreases
 in  the post  flame  zone.  (  3/17)   iowever,  the rate of dis-
 appearance in  the  post flame  zone  is  relatively slow in
 lean flame,  but  appears to  be quite  rapid  in rich flames.
 In lean flames containing fuel nitrogen it is very likely
 that NO values greater  than  equilibrium will be found.
The destruction  reactions for NO simply are  very slow.
The steps one can think of  are
                  0  +  NO   +   N   +   02
                 NO  +  NO   +   N20   + O
                 NO  +  RN   •*   •••-*•  N
                         16.

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all of which are slow compared to the stay time of a fluid




element in a flame.




         The general observations of NO formation from fuel




nitrogen are consistent with a mechanism in which the NO




is produced by the rapid reaction of an oxygen atom  (or




hydroxyl radical) with the parent compound or with a nitrogen




containing fragment.




         Bowman  ' proposes that the partial equilibrium




concentration of nitric oxide is related to the fuel nitrogen




concentration by assuming   the following reactions are




equilibrated:




         IX        fuel nitrogen   =   N~






          X        N2  +  2 0      =   2ND








         The oxygen concentration used in Reaction X is the




 partial equilibrium value calculated from





         XI        H  +  02  =  OH  +  0




        XII        0  +  H2  =  OH + H




       XIII        OH  +  H2 =  H20 +  H






         Use of these reactions, together with the partial




equilibrium assumption, thus permits the calculation of




the maximum NO concentration in  the flame zone without




knowledge of the detailed kinetics of the process by which
                         17.

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fuel nitrogen is converted to nitric oxide.  It should



be emphasized that Reactions ix and X are not the kinetic




route in the fuel nitrogen case,  but only a means of



calculating the maximum NO formed in the combustion zone



through an equilibrium technique.  In calculating the



maximum NO in this situation, one is ignoring the reactions



which would remove NO.  Recall these removal reactions are



thought to be very slow.   Thus in conclusion, one can



generally assume  that the NO formation from flames in



which the fuel contains bound nitrogen is greater than



the equilibrium value calculated  from the adiabatic flame



temperature for the particular fuel-air mixture ratio.
                       18.

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                    VI.  REFERENCES
 1.  Bowman, C. T.,  "Kinetics of Nitric Oxide Formation in
     Combustion Processes," paper presented at Fourteenth
      (International) Symposium on Combustion, Penn State
     University, 1972.

 2.  Classman, I. and Sawyer, R. F., "The Performance of
     Chemical Propellants," Technivisio'n Services, Slough,
     England, 1970.

 3.  Hottel, H. C. and Hawthorne, W. R., "Diffusion in Lami-
     nar Flame Jets," Third Symposium  (International) on
     Combustion, Williams and Wilkens, Baltimore, 1949.

 4.  Zeldovich, Jr., "The Oxidation of Nitrogen in Combus-
     tion and Explosions," Acta Physicochemica URSS 21,
     577  (1946).

 5.  Martenay, P. J., "Analytical Study of the Kinetics of
     Formation of Nitrogen Oxide in Hydrocarbon-Air Combus-
     tion," Comb. Sci. and Tech. , !L, 461 (1970).

 6.  Fenimore, C. P., "Formation of Nitric Oxide in Premixed
     Hydrocarbon Flames," Thirteenth Symposium  (International)
     on Combustion, Combustion Institute, Pittsburgh, Pa.,
     1971, p. 373.

 7.  Livesey, J. B., Roberts, A. L. and Williams, A., "The
     Formation of Oxides of Nitrogen in Some Oxy-Propane
     Flames," Comb. Sci. and Tech., 4_, 9 (1971).

 8.  Bowman, C. T., "Investigation of Nitric Oxide Formation
     Kinetics in Combustion Processes: The Hydrogen-Oxide-
     Nitrogen Reaction," Comb. Sci. and Tech., 3_, 37  (1971).

 9.  Bowman, C. T. and Seery, D. J., "Emissions from Con-
     tinuous Combustion Systems,"  (W. Cornelius and W. G.
     Agnew, Eds.) p. 123, Plenum, N.Y., 1972.

10.  Thompson, D., Brown, T. D. and Beer, J. M., "The Forma-
     tion of Oxides of Nitrogen in a Combustion System,"
     Paper presented at the 70th National A.I.Ch.E. Meeting,
     Atlantic City, N. J., Aug. 1971.

11.  Sarofin, A. F. and Pohl, J., "Kinetics of NO formation
     in a Premixed Laminar Methane Flame," Fourteenth
     Symposium (International) on Combustion, Combustion
     Institute, Pittsburgh, Pa. (in print).
                          19.

-------
12.  Iverach, D. Basden, K. S. and Kern, N. Y., "Forma-
     tion of Nitric Oxide in P'uel-Lean and Fuel-Rich
     Flames," Fourteenth Symposium (International) on
     Combustion, Combustion Institute, Pittsburgh, Pa.,
     (in print).

13.  Fenimore, C. P. and Jones, G. W., "Oxidation of Ammonia
     in Flames," J. Phys. Chem.,  65,  298 (1961).

14.  Bachmaier, F., Eberius, K. H. and Just, Th. , "The
     Formation of Nitric Oxide and the Detection of HCN
     in Premixed Hydrocarbon-Air Flames at 1 Atmosphere,"
     Comb. Sci. and Tech. 1_> Nos. 1 and 2  (in press)  (1973).

15.  Eberius, K. H. and Just,  Th., "NO Formation in Rich
     Flames: A Study of the Influence of the Hydrocarbon
     Structure," in "Atmospheric  Pollution by Aircraft,"
     AGARD Conference Proceedings (in press) (1973). AGARD/
     NATO, APO New York 09777.

16.  Martin, G. B.  and Berkau, E. K., "An Investigation of
     the Conversion of Various Fuel Nitrogen Compounds to
     Nitrogen Oxides in Oil Combustion," Paper presented at
     the 70th National A.I.Ch.E.  Meeting,  Atlantic City,
     N. J.,  Aug. 1971.

17.  Maclean, N. D. and Wagner, H. G.,  "The Microstructure
     of the  Reaction Zones  of  Ammonia-Oxygen and Hydrazine-
     Decomposition  Flames,"  Eleventh  Symposium (International)
     on Combustion,  Combustion Institute,  Pittsburgh,  Pa.,
     1967.
                        20.

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                   FIGURE CAPTIONS
Figure 1     The Adiabatic Equilibrium Flame Temperature
             as a Function of Equivalence Ratio
Figure 2     The Structure of Diffusion Flames: a) Droplet,
             b) Fuel Jet
Figure 3     Concentration Variation as a Function of
             Time in a Reacting Hydrocarbon-Air Mixture
              (Temperature in °K).   (From Ref.  5)
Figure 4     Comparison of Measured and Calculated NO
             Concentration Profiles for Combustion of
             Lean and Rich CH4-02-N2~Ar Mixture Behind
             Reflected Shock Waves. Initial Post-Shock
             Conditions: T = 2960K, P = 3.2 atm.  (From
             Ref. 1)
Figure 5     "Prompt NO" as a Function of the Ternperc ture
             in Various Mixture Strengths   in Adiabatic
             Propane-Synthetic Air Flames. (From Ref. 15)
                          21.

-------
<-—
                                   Fig. 1
          22.

-------
f
                            Fig.  2
            e  L
 23.

-------
                        Fig. 3
24.

-------
                                                                               eq.
      1.2
 O
 s
oo
 Z

 2    0.8
 u
 Z
 O
 u

 ^-   0.4
 O
 Z
                       0.2
0.4             0.6


   TIME - MSEC
0.8
1.0
                                                                         Fig.  4
                                              25.

-------
  J  -
100
 80
 GO
20
 0
      pprn NO
       X--. 1.4
x= 1.2
                                            *X=1.0
                                                  + X = 1,1
                                                   o
                                              •* ~
                                              /t."
                 1.2
             1f>00
                   2100
                                       TEMPERATURE
:si
                                            Fig. 5
                             26.

-------
 NO  - Control and Problems in
   j£
         Mobile Sources
        William Balgord
No Abstract or Paper Submitted
            27.

-------
      Air Quality Benefits  and  Costs  From
            Utility  NO   Regulations
                     X
                     by
         Peter C.  Freudenthal,  Ph.D.
     Chief Air Quality Control  Engineer
Consolidated Edison Company  of  New York,  Inc,
  Presented at Middle Atlantic Consortium
      on Air Pollution NO  Symposium,
       New York City Apri$ 26, 1973

-------
                    List of Illustrations


Figure 1  Off-stoichiometric burner operation in a front wall fired utility
          boiler.  Lower burners are operated fuel rich, and upper burners,
          fuel lean.UJ


Figure 2  Nitric oxide emissions from front wall fired boiler during normal
          and off-stoichiometric firing as a function of load.


Figure 3  Nitric oxide emissions from tangentially fired boiler during normal
          and off-stoichiometric firing as a function of load.  (Oil fuel)


Figure 4  Nitric oxide emissions from tangentially fired boiler during normal
          and off-stoichiometric firing as a function of load.  (Gas fuel)


Figure 5  Annual average nitrogen oxides concentration (ppm) attributable to
          Con Edison operations during 1972.


Figure 6  Diurnal cycle of hourly concentrations of NO, CO, and S0_ during
          July-December 1971.
Figure 7  Photograph of plume from Ravenswood Generating Station rising over
          polluted air of New York City during episode of 28 October 1966.
                               29.

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                            ABSTRACT








     Con Eidson has  conducted NO   emission reduction tests which have
                               A


demonstrated the applicability of  off-stoichiometric firing as a control




technique on certain boilers.   Con Eidson's emissions produced a maximum of




0.004 ppra of NO  at  ground  level in New York City,  and if City emission
               X


standards can be achieved,  ground  level concentrations are expected to be




reduced 0.0016 ppm below existing  levels.   The  benefit from such an in-




significant improvement  in  air quality  is  questioned in light of the high



cost of the emission control.
                             30.

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INTRODUCTION






     Much of the attention  towards improving; nitrogen dioxide concentrations




in urban air has been directed  towards control of emissions from large electric




generating stations.  The most  stringent of these regulations are the NO
                                                                        X


emissions limitations contained in the New York City Air Pollution Code.



Following enactment of  this  code in November 1970, Con Eidson began a program



to determine the extent  to which nitrogen oxide emissions from its boilers could



be reduced.  This paper  discusses the techniques of control which Con Edison has



applied, and evaluates  the  improvement in air quality which would be expected



if the New York City NO  emissions standards are achieved.
                       X



     Several boilers of  the  Con Edison system have been tested for nitrogen




oxides emissions reduction.  Two of these boilers, because of their differing




design, provide examples of  the available control techniques and the emission




reductions which may be  achieved.    These boilers are Astoria 20 which is a




front wall fired, 170 MW, Babcock & Wilcox boiler, originally coal fired but




now burning oil and natural  gas,  and Ravenswood 20, which is a tangentially




fired 385 MW Combustion  Engineering furnace.  This furnace is divided, and




therefore each section might be considered as 193 MW each, and size comparable



to the Astoria 20 boiler.  Ravenswood 20 was originally designed for coal,



although coal burning facilities  were never installed.  This boiler has only




been operated on oil and gas.






EMISSION CONTROL TECHNIQUES




     The method used for reducing nitric oxide formation was off-stoichiometric




burner operation.  The concept  of this method is that by reduction of flame




temperature below 3,000  F, there  should be appreciable reduction of nitric




oxide formation.  Off-stoichiometric firing involves manipulation of existing




burners, and generally does  not require reworking of existing equipment.  This
                                 31.

-------
firing method (Figure 1)  involves first operating the top of the furnace


lean (more excess air) and then at the same time the bottom section fuel


rich (less than theoretical air).  Both the fuel rich and the fuel lean burners


result in lowering the flame temperature;  and the lower temperature yields less



NO  .
  x

     The actual burner pattern selected for maximum NO  reduction will vary
                                                      X


from one boiler to another.  Generally speaking, it is preferable to choose


the lower burners to be fuel rich, so any CO and smoke can be burned off in


the air-rich upper section of the furnace.


     To accomplish this two-stage combustion firing, the fuel was turned off,


and air left full on to some of the burners in the top row.  Fuel pressure was


then raised  to compensate for the burners which were out of service, and the


air dampers  of some of the bottom row of burners were then closed.


     This procedure produced smoking in all cases when the burners were not in


good condition.


     Final trimming of the air/fuel ratio was accomplished by adjustment of the


air only.  By trying various combinations of burners in and out of service,


and by manipulating oil pressure and air, NO  formation was minimized.


     Unfortunately, this manipulation is extremely difficult to accomplish.


Other factors, such as output and steam temperature must be maintained, and


some low velocity coal burners converted to oil will not tolerate much reduction


in air before  excessive smoking occurs.



EMISSION REDUCTION



     The emission reduction achieved at Astoria 20, the 170 MW front wall  fired


unit,  is shown in Figure 2.  The upper curve shows the NO  formation during
                                                         X

normal operation expressed as a percent of the maximum NO  level, as a function
                                                         X

of load.  The lower curve shows the "best" off-stoichiometric results.  Note


that smoking became unavoidable over 140 MW, although a 37% reduction in NO
                                                                           x


                                32.

-------
 operation was  achieved  up  to nameplate rating, although not to peak.  In order



 to keep  the  furnace  in  balance  during the series of experiments, burners were



 turned off two at  a  time,  and at  opposite corners of the furnace.



     Emission  reduction curves  for  gas-only  firing are presented in Figure 4.



 During normal  firing conditions,  load on this boiler had to be restricted



 to below 300 MW to avoid excessive  temperatures.  Off-stoichiometry alleviated



 some of  these  steam-temperature problems, because when all of the top tier of



 burners  were operated "air only", the flame  was effectively lowered within



 the furnace.



     Although  substanital  NO  reduction were achieved furing test conditions,
                            X


 the practical  ability to reduce NO  may be somewhat less.  The best patterns



 for NO   reduction  may not  be compatible with long-term and safe operation of
      X


 the boiler.  Some  compromise in NO  levels must be accepted rather than operate
                                  X


 with high CO or too  close  to a  smoking condition.




 AIR QUALITY




     The success of  this or any other emission control program can be measured



 by the resulting improvement in ambient air  quality.  In order to assess the



 improvement in air quality, the total impact of Con Edison's NO  emissions on
                                                               X


 New York City's environment was estimated through the use of a meteorological


                 (2)
 diffusion model.      This  model, which was developed for the Environmental



 Protection Agency's  evaluation  of Implementation Plans, calculates annual



 average ground  level  concentrations, given an emission inventory and a set



 of climatological  data.  The model  had been  tested for sulfur dioxide, and was


                                                                         (3)
 shown to be accurate within a factor of 2 for both point and area sources.



Because the modeling  techniques for elevated point  sources are less complex



and the emissions  inventories are more accurate than for area sources, the



accuracy for point sources  is probably much  greater.



     The total NO  emissions from each Con Edison stack during 1972 including
                 X


gas turbines, were entered  into the computer program, along with stack




                                33.

-------
temperatures, velocities, locations, heights, and diameters, and five year



climatological data from LaGuardia Airport.  Calculated ground level N0x



concentrations attributable to Con Edison operations are shown in Figure 5.



     The peak NO  concentrations, which is calculated to occur in Queens, was
         ^      x


about 0.004 ppm.  This peak concentration represents a mixture of both NO and



N0?, but primarily the former.  Boiler emissions of 'oxides of nitrogen are



usually over 90% as NO, for which there is no air quality standard.  It takes



minutes to hours for NO to oxidize to N0?, and during the time oxidation occurs,



there is additional dispersion, making the peak NO  concentration from Con Edison



much less than  indicated in Figure 5.  The most conservative way to compare the



estimated concentrations with the air quality standard would be to assume that



these concentrations represent 100% NO .   Assuming this, Con Edison contributed



only about 8% of the Federal primary and secondary N0? air quality standard



during  1972.



     The significance of this concentration is demonstrated by comparison to air



quality measurements in New York City.  NO  is measured at five stations in



New York City - 121st Street, 45th Street, Canal Street, Astor Place, The



Brooklyn Public Library, and Morrisania,  Bronx.  Only one station reported a



full year's  data in 1972, but two operated for 11 months, one for 8 months, and



two for 7 months.  All stations reported  average N0? concentrations of 0.03 ppm



or  less, indicating that the primary and  secondary air quality standard has been


achieved.



     Even is Con Edison could totally cease NO  emissions, it would be impossible
                                              X


for epidemiologists to detect and improvement of public health - and this is



what emission control is all about.



     The reason for the extremely low impact of Con Edison's NO  emissions on
                                                               x


ambient  air  quality is  the very high effective stack height of its plants.  Most
                               34.

-------
of  the  stacks  are  300-500  feet  tall,  and because of the concentration of heat



released  at  the  stack exit,  the plumes  typically rise hundreds of feet above



the  stacks.  The result  of this high  effective  stack height is that nearby



the  stacks there is  nearly zero impact  at  ground level.  Downwind the plumes



disperse  in  both the vertical and  horizontal  directions, and finally the bottom



edge of the  plumes reach the ground.  But  by  then dispersion has reduced trace



gas  concentrations to very low  levels.



      An example  of the benefit  of  high  effective stack height is presented in



Figure  6.  The photograph  was taken during and  air pollution episode, because



during  an episode, the air becomes so laden with particulates that the resultant



haze becomes photographable.  The  plume well  above the inversion layer seen



from the  Ravenswood  Generating  Station  is  observed dispersing.  It is apparent



that the  plume is  not contributing to the  polluted air near the ground.



      Aerometric  data analysis supports  the hypothesis that Con Edison, because



of its  tall  stacks,  has  a  very  small  impact on  ambient NO  concentrations.
                                                         X


Figure  7  shows the diurnal cycles  of  CO, S0_  and NO from July through December



1971, as measured  at the New York  State Department of Environmental Conservation



monitoring station at Welfare Island.   Because  diffusion characteristics of



these gases  can  be assumed proportional to each other when they come from a



common  source, CO  can serve  as  a tracer for NO  emitted from automotive traffic,



and  S09 is suited as  a tracer  for NO from fuel burning.  Although these tracers



distinguish between  stationary  and transportation sources, they do not dis-



tinguish between on-site boilers used for  space-heating and large boilers used



for  electricity  generation.



     All three curves  show an early morning peak concentration and a decline



during the late  morning  hours.   This  peak, which occurs when meteorological



dispersion conditions  are  at  their worst,  occurs at the hours when both traffic



is at a peak and S0_  emissions  are at a peak, because of the early morning





                              35.

-------
demand for hot water,  space-conditioning and electricity.  In the early



afternoon, when traffic begins to rise (center shaded area), both CO and NO



rise at equivalent rates, but SO  tends to remain constant.  This rise in NO



and CO occurs in spite of this being the best time of day for meteorological



dispersion.  In the late afternoon and early evening, S02 also rises as emissions



increase due to early evening demand for hot water, heat and electricity, and



meteorological dispersion worsens.  After midnight (left and right shaded areas),



SO  concentrations remain nearly constant, but CO and NO decrease rapidly as



traffic declines.  The coincidence of the nighttime decline and early afternoon



rise  of both CO and NO, which does not correspond to the S02 curve, strongly



suggests  the relationship of NO  ground level concentrations to automotive
                               X


emissions.  These curves would tend to confirm the conclusion presented above



based upon meteorological modeling, that power generation is not a significant



source of ground level NO .
                         X




COST-BENEFIT




    In November, 1970 New York City, assuming that an NO  problem existed, enacted



some  of the most stringent NO  limits in the entire nation - almost twice as
                             x


restrictive as the Federal new source standards.  These regulations, which were



aimed only at utility boilers, restrict NO  emissions to 150 ppm in existing
                                          X


plants and 100 ppm in new utility boilers.  If Con Edison is able to achieve and



maintain  these emission levels, the maximum annual average NO  concentration



attributable to the utility will be reduced by 0.0016 ppm at the area of maximum



impact.



      Although this reduction is insignificant in terms of health and welfare,  it



will  cost tens of millions of dollars.  The modifications to the new 800 MW



Astoria 60 boiler, through which Con Edison is attempting to achieve the never-



before attained level of 100 ppm, cost over 14 million dollars.  These costs will
                               36.

-------
be eventually borne by Con Edison's ratepayers.



     At the same time that the City passed these costly NO  emission restrictions,
                                                          X


it was curtailing its own environmental programs for lack of money - rat control,



removal of lead paint from walls in the ghettos, ragweed control.  Unfortunately,



no statistics are available to compare the number of asthmatic attacks which



will be avoided through the multimillion dollar public health expenditures for



0.0016 ppm NO  reduction from Con Edison boilers, versus the number of attacks
             X


which might have been avoided had the ragweed  control program, costing a few



thousand dollars per year, not been curtailed.
                                  37.

-------
SUMMARY AND CONCLUSIONS




     Nitrogen oxide emissions reductions have been achieved by means of



off-stoichiometric firing during carefully controlled test conditions on



several Con Edison boilers.  It is unknown, however, whether boiler operation



can be maintained at levels mandated by the New York City Air Pollution Code.



   The expected reduction of ambient NO  will be approximately up to 0.0016 ppm
                                       X


if Con Edison's emissions are reduced to legislated levels, but this change in



air quality will cost tens of millions of dollars.  Because of the insignificance



of this reduction in terms of air quality improvement and health and welfare



benefits, it seems appropriate that local environmental control strategies be



reevaluated.
Acknowledgment
     The author gratefully acknowledges the assistance of Messrs. George



Stegmann, Paul Giardina, and 0. G. Hanson of Con Edison's Mechanical Engineering



and Environmental Departments.  The emission reduction tests were conducted under



Mr. Stegmann's supervision.
                             38.

-------
REFERENCES
(1)  Seabrook, H. H. and B. P- Breen, A Practical Approach to NO  Reduction
     in Utility Boilers, presented at the American Power Conference,  Chicago,
     April 18-20, 1972.


(2)  TRW Systems Group, Air Quality Display Model, prepared for Department of
     Health Education and Welfare, Public Health Service, National Air Pollution
     Control Administration, Washington, D. C., November, 1969.


(3)  Freudenthal, P- C., P. A. Giardina, and K. Juris, Application of the Air
     Quality Display Model to New York City, presented at the Fall Annual Meeting
     of the American Geophysical Union, San Francisco, December 1971.
                                   39.

-------
'OFF-STOICHIOMETRIC11  BURNER OPERATION
                                      FIGURE  i

-------
       ASTORIA UNIT 20 - REDUCED NITRIC  OXIDE OPERATION
                              OIL FUEL
 gioo
 2
o
o
5  80
    60
    40
    20
o
oc
UJ
o_
       -JJ-
 BASELINE (NORMAL) OPERATION
70
                OFF-STOICHIOMETRIC
                    OPERATION
                                       A
                                 UNACCEPTABLE
                                    SMOKE


                              RECOMMENDED
                              FIRING PATTERN
                              LOW NITRIC OXIDE
                              FIRING PATTERN
                              DETERMINATION
         40
    60
80     100     120
    UNIT LOAD, MW
140
160      180

   FIGURE  2

-------
         RAVENSWOOD UNIT 20 - REDUCED NITRIC OXIDE OPERATION
                               OIL FUEL
                                 NORMAL OPERATION
   100
    80
    60
x   40
LU
O
20
     0
             100
                                          n
                              REDUCED NITRIC OXIDE OPERATION
                       200
300
400
                               LOAD - MW
                                                            FIGURE 3

-------
            RAVENSWOOD UNIT  20-NITRIC OXIDE REDUCTIONS
                        WITH NATURAL GAS  FUEL
- lOOr
O

9  80
 X
O
    60
    40
    20
                    BASELINE (NORMAL)
                       OPERATION
            100
                                          RECOMMENDED OPERATING
                                                CURVE
                     O  NORMAL 02
                     A  MINIMUM 02
                     D  MINIMUM NOxWITH
                         DESIGN STEAM
                         TEMPERATURES
200           300

     LOAD- MW
400
                                                           FIGURE 4

-------
FIGURE 5
     44.

-------
                                   FIGURE 6
                DIURNAL. CYCLE OF NO, SOi;  AND CO

                       JULY- DECEMBER  IS7I

           (WELFARE-ISLAND, MONDAY THRU FRIDAY AVERAGE DATA)
IU
Q

X
o

  Q.
cc a.
o _

UJ
X
O
o
U_
-J
Z>
CO
.050
     .000
                                                             LJ
                                                             O
                                                             X
                                                             o
                                                             2:
                                                             o
o
ffj
cc
<
o
                                HOURS
                                    45.

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FIGURE 7
    46.

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            FUTURE APPROACHES  TO  STATIONARY  SOURCE

                   CONTROL  OF  STACK  GAS NO
                                          x



                        BY:  A.J.  Tellera)






     Nitrogen  oxides  appear to present one of  the most formidable



pollution control problems  that we are encountering.  They are



emitted by all thermal  processes  as  well as  specific chemical



operations such as nylon  and nitric  acid manufacture and electro-



plating.  As a result,  nitrogen oxides represent the universal



pollutant.



     Early work by Chambers &  Sherwood(  , Denbigh and Prince( '

            (2)
and Carberry     shed  some light on a confusing situation.  Nitrogen



oxides do not  behave  simplistically  in the recovery -process of



contact with liquid.  Chambers and Sherwood  proposed a gas phase



mist reaction.   Denbigh and Prince found that  the data indicated,



the rate limiting reaction  involves  N?0, but that the rate of



absorption, V,  is related as follows:



     V = Ka  [N204J - C [N204]  1/4 [NO] 1/2



Carberry, in relative agreement with Denbigh and Prince establish-



ed that the key  reaction  involves N_0, and precludes a gas phase



reaction.



     However,   it is acknowledged by  all investigators that the



formation of NO,., whose  concentration is limited from thermodynamic



implication but whose equilibrium attainment is rapid, may very well



enhance the absorption of nitrogen oxides and may also contribute



to the gas phase reaction and misting observed by Chambers and



Sherwood.




     a)
         Mr.  Teller's paper was presented by Mr. O'Neall of Teller Environmental

         Systems Inc.
                                     47.

-------
     Dekker, Snoek, and Kramers(7) confirmed the N^ mechanism  of



 absorption  in water or caustic solutions and indicated, in agreement  with



 Sherwood, that the system could be gas phase controlling at high concentration



 nitrous gas systems, but also agreed with Denbeigh and Carberry  that  it  could



 be  liquid phase controlling at low nitrous gas concentrations.



     Koval  and Peters (14') indicated that the mechanism of N0x absorption was



 far more complex than indicated by previous investigators and included the



 effect of an increasing inventory of HN02 during the absorption  process.  The



 model developed and reasonably confirmed by experimental data are
     -d  (e N02)g = kc (N02)g" + kd (N0)g (N02)g - k£


          dt




     -d  (NO)  = k, (NO)  (NO.)  - k  (HNO )2
     	g    d     g    2 g    e     2.

         dt



     The major concern from the aspect of pollution control is that only in



limited circumstances is nitrogen dioxide (or equivalently nitrogen tetroxide)



of major concern.  In the case of combustion gases emitted from power plants,



incineration,  steel,  glass, non ferrous metal manufacture, the sources of the



major quantities of NO  emissions, the significant specie of the gases is
                      A.


nitric oxide.



     Additionally the nitrogen oxides are often emitted in streams combined



with SO  resulting in the additional conversion of N0_ to NO via reaction
       £-                                             v£



           S02 + N02  = S03  + NO




     Even were NO  to be absorbed, NO is created by the approximate overall



stoichiometric reaction  (Koval and Peters correction not applied)




           3 N03  + H20 = 2  HNO  + NO




     Thus the  pollution  problem we encounter in products of combustion is to
                                48.

-------
a major degree the problem of nitric oxide control, the removal of a



relatively insoluble unreactive gas and to a minor degree the removal of



a soluble NC>2 which process releases NO equivalent to 1/3 of the noxious



material removed.




     In the case of chemical processing, munitions destruction, and plating,



the pollution problem is related  to nitrogen ioxide control, but here again



the creation of nitric oxide during the liquid gas absorption process presents



a formidable problem.




     As established by numerous investigators and confirmed recently by Morrison,



Rinker, and Corcoran     , the oxidation rate of nitric oxide by oxygen to



nitrogen dioxide is extremely slow, NO, in concentrations of 10 - 50 PPM in



oxidized by oxygen to 80% completion only after 150 - 500 minutes contact



time.



     Since federal legislation is directed to achievement of emission levels



in the order of 100 PPM total NO  , recovery or preventative methods beyond mere
                                X


absorption of N0« are indicated.



     Preventative control is achievable in combustion processes and in plating



operations.



     For example, the use of tangential firing and gas recycle in boiler operation



has resulted in the reduction of NO  emissions from the range of 1000 PPM a
                                   X


range of 50  - 150 PPM.  These achievements have resulted in the establishment



of emission  standards by EPA of 150 - 200 PPM for liquid fuel fired operations



and 400 - 500 PPM for coal fired operations.
                               49.

-------
                                                            /Q\
     Performance of operating systems reported is as follows


FUEL       FIRING                          CAPACITY - MW       ^ ~ PPM

Gas        Tangential                           32°
           10-15% Recirc.
           40%

Gas        Wall Fired
           Off Stoichiometric                   480               150
           Comb. - Equivalence
           Ration 1.3 - 1.4

Gas        Wall Fired                           750               120
           Off Stoichiometric

Oil        Wall Fired                           480               185 - 210
           Off Stoichiometric

           Wall Fired                           180               187
           Off Stoichiometric

Coal       Tangentially Fired                   320                85
           15% Recirculation

           Tangentially Fired                   125               200

     A second method of suppressing NO  emissions is the introduction of

                       (13)
urea into plating baths    .   It is reported by Kerns that the NO  emission

was reduced to less than 1 PPM as compared with normal emissions of 8000 PPM

when the concentration of urea was 6 oz/gallon in a 40% nitric acid solution.

     In the nitric acid industry, the major process application for reduction

of NO  emissions is the catalytic reduction of the nitrogen oxides.  Both
     X

methane and hydrogen are used as reducing agents over a platinum catalyst.  Both

spherical catalysts and honeycombed catalysts are used in the conversion of

nitrogen oxides to nitrogen.   Federal standards, based on existing performance,

were established as 3 Ib NO /ton HNO , which is equivalent to 209 PPM.  In actual
                           X        J

plants tested, catalytic reduction using methane achieved a low level of 110 PPM

in the exhaust gas with the average plant emitting at the level of 310 PPM.

Where hydrogen is used as a reducing agent, the emissions range from 50 - 150 PPM

     Where N0_ is a major component of the emissions such as potassium
                                   50.

-------
permanganate     has resulted in s uppression of nitric oxide formation.



has, via introduction of a high liquid turbulence, increased the overall rate



of absorption of N02 by 25%.  The use of FeSO, solutions for absorption of NO



results in the creation of a coordinate-covalent adduct that permits total



absorption of N02 in non-oxidizing media.



     Major activity, recently has been devoted to avoiding the use of liquid



gas contactors for NO  recovery because of the equilibrium limitations.  The
                     X


activity has been divided into three areas



     1.  Catalytic reduction of nitrogen oxides.



     2.  Adsorption on silica or molecular sieves.



     3.  Ab-adsorption on chromatographically active materials.



     The major emphasis on the reduction of nitrogen oxides to nitrogen has



been on the study of copper based catalysts (1, 4, 16, 17, 18, 19).  In all



cases the reaction is related to the reduction of NO  compounds by reducing
                                                    X


agents, primarily CO, over a copper based catalyst.
Adsorption of NO  on silica gel and molecular sieves has been report
                X
                                                                         ed



Problems of interference by water vapor in molecular sieve work has been



encountered.  However, pilot plant results reported by EPA indicate a reduction



of NO  from the 1000 PPM concentrations range to 50 PPM.
     X


     The third area, that is the ab-adsorption on chromatographically active



material, is in an early stage of development.  Selective ab-adsorption on



TESISORBS are indicated.  These are potentially capable of regeneration and



early studies to this and are in progress.



     All three of the more recent approaches to NO  control attempt to avoid the
                                                  X


inherent limitations of the liquid-gas systems where equilibrium causes the



production of a relatively insoluble NO or where the liquid capability as a



solvent of NO is limited.  It appears that economics will eventually direct much



of our efforts to low-energy consuming control systems such as minimizing NO
                                                                            X


formation, and that in recovery systems, solid gas systems will prevail.





                               51.

-------
                            BIBLIOGRAPHY


 (1)  A.  Bauerle, ACS Div. Petrol. Chem.,  1971, 16(2), E70-72

 (2)  J.J. Carberry, Chem. Eng. Sci, 9(4),  189-195, (1959)

 (3)  F.S. Chambers and T.K. Sherwood, JACS, 59, 316,  (1937)

 (4)  H. Chien, ACS Div. Water, Air, Waste  Chem, Gen Paper 1971,
           11(1), 71 0 75

 (5)  J. Collins, U.S.P. 3674429

 (6)  K.G. Denbigh and A.J. Prince, Trans.  For. Soc.,  790-801,  (1947)

 (7)  W.A. Dekker, E. Snoek, H. Kramers, Chem.  Eng. Sci, 11, 61-71,  (1959)

 (8)  EPA -- Fossil Fuel Fired Boilers (1972)

 (9)  EPA — Nitric Acid Plant Survey (1972)

(10)  J.W. Fleming and G.L. Nosine, U.S. Army  CRLR 439,  (1955)

(11)  S.N. Ganz, J. App. Chem. USSR, 30(5),  732, (1957)

(12)  R. Kazakova, Inf. SGN - IPIAPPOS,  No.  6,  229-49, (1971)

(13)  B.A. Kerns, IEC Proc. Des.  & Dev. , 4(3),  263-266,  (1965)

(14)  E.J. Koval and M.S.  Peters,  IEC, 52(12),  1011-1014,  (1960)

(15)  M.E. Morrison,  R.G.  Rinker,  W.H. Corcoran, I. &  EC Fund, 5(2) ,

(16)  J. Sorensen, IEC Prod.  Res.  Dev.,  11(4),  423-6,  (1972)

(17)  U.S.P.  3702236,  1972

(18)  U.S.P.  3682585

(19)  U.S.P.  3701823
                                52.

-------
             NO  - CONTROL BY WET SCRUBBING
               x
                            by

                      Robert S. Kapner
                    Engineering Division
                     The Cooper Union
                       Prepared for
Symposium on the Current Status of the NO  problem and its control
                                         X

      Middle Atlantic Consortium on Air Pollution (MACAP)
    April 26, 1973       CUNY, GRADUATE CENTER, NY,  NY
              Elmar R. Altwicker, Ph.D., Chairman

-------
Introduction

      On approaching the problem of the control of nitrogen oxide emissions

from stationary sources, one is confronted with several possible methods

that would appear to  offer promise of providing a satisfactory technical and

economic solution.  Among the  methods that have been proposed are:


      (1)    Process  and equipment modifications which reduce
            NOX  emissions by changing either equipment design
            or operating procedure.

      (2)    Removal of nitrogen oxides  after they have been pro-
            duced in  combustion or manufacturing processes by

            a)    reduction of NO to  N2 and Oo
            b)    absorption by wet scrubbing
            c)    adsorption onto solid sorbents

      Most popular,  at the present time, are methods involving process

and  equipment modifications such as two-stage combustion, flue gas

recirculation,  fluid bed combustion,  and tangential firing - all applicable

to fossil-fuel combustion systems (power generation,  steam generation,

domestic and industrial heating, incineration) which is the single largest

contributor to nitrogen oxide emissions from stationary  sources.


      Part of the reason for the popularity  of the process and equipment

modification approach is that  it attacks  the problem of NOX emissions

directly at the  point of NOx formation - in the combustion chamber.   To

some extent, also,  part of the reason for the popularity  of the modification

approach is the failure to quickly and unequivocally  find a control system

among the removal methods which has proven to be completely satisfactory
                                    54.

-------
for abating NOX emissions from stationary sources.  The same pattern

can be observed in NOX abatement programs from moving sources,  where

the focus of control has shifted somewhat from catalytic removal methods

to engine modifications which are aimed at preventing NOX formation.


      Despite the  popularity of modification methods, it is strongly  felt

in some quarters,  that removal systems still hold promise of providing

solutions to the NOX emission problem, from both moving and stationary

sources.  It is the purpose of this  paper to review proposed wet scrubbing

systems having potential  for NOX abatement from stationary  sources.


      From one point of view,  wet scrubbing systems for NOX control

can be grouped according to the type of scrubbing solution used, the

nature of the products formed  upon absorbing NOX) the ease  with which the

scrubbing solution can be regenerated,  and the economic value of materials

recovered from scrubbing systems.


      A classification of  this type would include:

      (1)   Scrubbing solutions which upon absorbing NOX are consumed
           or transformed into intermediates that are  difficult to
           regenerate  and have low economic value.   Examples include
           urea,  which is decomposed upon absorbing  NOX,  and sulfite
           and bisulfite  solutions  which are converted  to sulfates by
           NOV absorption.
              J"i.

      (2)   Scrubbing solutions which produce intermediates that can be
           regenerated by chemical and thermal means along with
           nitrogen salts that have some economic value.  Examples
           include alkaline scrubbing  by magnesium  and calcium oxides
           to form nitrites which  can  be converted to nitrates by thermal
           and chemical processes.
                                    55.

-------
       (3)   Scrubbing solution which complex NOX gases upon absorption
            and which can be regenerated by heating, the regeneration
            step releasing NOX in concentrated form.  Examples include
            aqueous solutions of some  inorganic salts, organic  solvents
            and organometallic materials.
      This paper will explore only the latter two categories, and then

 rather narrowly, by examining selective examples which show the greatest

 potential for practical application.


      Although NO  is the principal constituent in the general designation

 NOX, we shall have to treat at least three other nitrogen oxides which play

 an important part in wet scrubbing absorption processes.  In addition to

 nitric oxide (NO) these are, nitrogen dioxide (NO2) and its equilibrium

 dimer,dinitrogen dioxide (N2O4) and dinitrogen trioxide (N2Os) which,

 although a true compound,  can be considered to be an equimolar mixture

 of NO and NO2.


      The extent to which one or all of these nitrogen oxides is present  in

 a stack emission depends somewhat on the nature  of the source,  but there is

 also a major dependency on the concentration level of the total nitrogen

 oxides present and  upon the physical state of the stack gas, particularly

 its temperature.  At ordinary temperatures, NO is readily oxidized to

 NO2  in the presence of  oxygen which is almost always available from excess

air used  in combustion processes and in some chemical operations such as

nitric acid manufacturing.  Where NO2  is easily produced by NO oxidation,
                                    56.

-------
the" presence of the other oxides of nitrogen are automatically ensured,

and when NO2 is not easily formed it is sometimes necessary to arti-

ficially introduce it as a preliminary step in wet scrubbing systems.
NITROGEN OXIDE SCRUBBING SYSTEMS -
WATER, BASIC AND ACID SOLUTIONS
      A description of control methods for the removal of nitrogen oxides

from stationary emission sources by wet scrubbing methods properly begins

with an examination of the more obvious chemical properties of nitrogen

oxides, particularly their solubility and reactivity with water and with

aqueous solutions of acids and bases.   Quite a bit is known about these

systems and they have been studied with great interest because of the

importance of their industrial applications.



Wet Scrubbing With Water

      Nitric oxide is the most stable and nonreactive of all the nitrogen

oxides present in stack emissions.  It  is only sparingly soluble in water,

about 1.5  times that of oxygen at ordinary temperatures.  Although

Partington (1) reports that  NO disproportionates in water to form N2O3 and

the rate is exceedingly slow and NO is generally considered nonreactive.

Nitric oxide is also inert to aqueous solutions of acids or bases and in

fact can be  purified by bubbling through H2SO4 and KOH to  remove water
                                     57-

-------
and NO2 respectively (2).





      The other oxides  of nitrogen,  however, are quite reactive with



water.  The overall reaction of NO2 with water is given by





      3NO2 + H2O = 2HNO3 + NO                                  (D





      This single equation is often used to represent the commercial



production of UNO3 although it is  known to actually  proceed in a number



of complicated steps.  It is generally conceded that although NO2 and its



dimer N2O4 are soluble in water, the chemical absorption of the dimer is



of far  greater importance than the physical absorption of NO2 especially



at high concentrations of NO2 in the gas phase.  The route to HNO3 by



N2O4  absorption is described by  equations (2)  - (5):





      N2°4 + H2°  =  HNO3  + HNO2                             (2)



            3HNO2   =  HNO3 + 2NO + H2O                         (3)



         2 NO + O2  =  2NO2                                       (4)



            2  N02    =  N204                                       (5)







The nitrous acid produced by NO  absorption,  equation (2), is
                              c* ft


decomposed to produce nitric acid and  nitric oxide , equation (3).   The



process of HNO3 production initiated by N2O4 absorption can continue



only at high concentrations  of NO.  The oxidation of NO to NO2 by oxygen



in air  in the absorption column, equation (4), followed by dimerization of
                                   58.

-------
N02  to N204, equation (5),  are critically dependent on NO concentration.



Initially,  this reaction sequence predominates, but as nitrogen is removed



from the  gas  phase and appears as nitric acid in  the liquid,  the concentra-



tion of NO becomes too low for reactions (4) and  (5) to produce significant



amounts of N2O4.  Instead,  toward the end of the absorption process,



when NO2 concentration is relatively low, a second mechanism predominates.



This is the absorption  of N2O3,  formed from NO and NO2 in the gas phase,



to produce nitrous acid which decomposes to form nitric acid and nitric



oxide.





            N2O3  +  H2O     =    2HNO2                           (6)



                   3HNO2       =    HNO3 + 2NO + H2O                (3)



                   2NO + O2    -    2NO2                             (4)



                   NO  + NO2   =    N2O3                             (7)







Although the route to HNOg by NgOg  absorption is most important at low



NO and NO9 concentrations,  it must  also occur at high concentrations
           &


since NO  is everywhere produced by the decomposition of HNO2 - however



formed.  The overall scheme of nitrogen oxide absorption to produce



nitric acid is  shown in  Figure I as described by Hoftyzer and Kwanten (3).





      The steps describing nitric acid production by N2o4,  NOg and




N2 °3  absorption cannot continue indefinitely.  When the concentration of



nitrogen oxides becomes too low to support reasonable reaction rates,  the
                                    59.

-------
 remaining nitrogen oxides are discharged.  The irony of the problem of




 removing nitrogen oxides from discharged nitric acid absorption column




 tail gas by wet scrubbing is only too apparent at this point.  If the NOX




 concentrations are too low  to efficiently absorb in water, then wet scrubbing




 with water would appear to hold little promise as an emission control




 method.  Although NOX removal at low concentrations is difficult, it can




 be accomplished.   For example, in some older nitric acid manufacturing-




 processes the nitrogen oxides in the tail gas have been scrubbed clean by




 contact with aqueous Na0CO9 although this method is not practiced in
                        £j    *^



 modern,  high pressure nitric acid plants.








 Wet Scrubbing With Alkaline Solutions^




      That a carbonate solution can potentially absorb nitrogen oxides




 effectively at concentrations too low for efficient absorption in water (or




 dilute HNOg), introduces the next set of systems, alkaline and carbonate




 wet scrubbing for controlling NOX stack emissions.   The reaction schemes




 here are quite similar to those described for scrubbing nitrogen oxides




 with water and are shown in Figure 2.






      A significant advantage is realized with alkaline or carbonate




 scrubbing solutions in that  the nitrite formed from N2O4 or N2O3 absorption




 is stable in basic solution and does not decompose to form NO as does




 its acid analog HNO2 in acid solution.  This  is the principal idea behind




 the use  of aqueous NaOH as the absorbing medium in sampling for atmos-



pheric NOX.






                                     60.

-------
      Because of the apparent potential for wet scrubbing low concentra-




tion nitrogen oxides in basic solutions, considerable effort has gone into




studies whose goal was finding an aqueous alkaline or carbonate system (or




mixture) which could effectively be used  for cleaning stack gases as well




as the best conditions for performing such processes.   The outcome of such




studies has  been a large number of publications in the  technical literature




on NOX scrubbing systems, a  steady issuance of patents on alkaline and




carbonate scrubbing systems, an examination of existing wet scrubbing




processes for SOg control using alkaline materials for  simultaneous control




of nitrogen oxides and, finally, more than a little  confusion as to the prac-




tical performance of such methods.






      Some  idea of the range  of studies found in the literature is shown in




Table  1 which represents a small but typical selection  found.  A search of




Chemical Abstracts for  the period 1962 - 1972 revealed some 60 articles,




mostly Russian,  on the subject of alkaline and  carbonate scrubbing systems.




In addition there have been at least two major studies on wet scrubbing per-




formed for the U. S. Environmental Protection Agency during the last




two years (4,5).   One of these studies is experimental  (Chappell, ref. 5)




and is abstracted  in Table 2.






      One of the chief variables affecting the extent and rate of absorption




of NOX is the ratio of NO2/(NO + NO2), denoted by a in Tables 1  and  2.




Most of the literature on NO   absorption examines the  particular region
                           .A.
                                    61.

-------
 a  - 0.5 which on a scale from zero (pure NO) to 1 (pure NO2), corresponds




 to a mixture with an average composition of N2O3.  The importance of this




 particular concentration ratio of nitrogen oxides in wet scrubbing systems




 deserves special attention.






      It was noted previously that N2O4 and N2O3 were the active species




 in NOX absorption, not NO.  However,  upon absorbing N2O4 or N2O3 in




 water or an acid medium,  nitrous acid  is produced which then forms nitric




 acid and NO.  Thus, the ability to absorb nitrogen oxides depends upon the




 ability to form N2O4 and N2O3 from NO.  Even for scrubbing systems in




 which NO is not produced, alkaline mediums,  for example, it is necessary




 that the NO in the gas  to be scrubbed be converted to NO2 so that either




 N2 04 or N2O3 can be  formed.   At high concentrations of NO and  in the




 presence of air,  NO2 and its dimer N2O4 will readily result.  Unfortunately,




 the ability to form N2O4 under normal stack conditions is almost nil due




 to the low concentration of NO in emission sources and the rather high




 temperatures that accompany many stationery emissions.  The effect of




 temperature and  concentration are treated in considerable detail  elsewhere




 (6, 7) and will be  discussed only briefly here.







      Consider temperature first.  At temperatures below about  140°F




as much  as 50% of the  NO2 in a  gas will be present in dimer form. As




temperature increases the equilibrium  amount of dimer present will rapid-




ly  diminish.  Above about 280 F virtually no N2O4 will exist.  In addition,




the oxidation rate of NO to NO2  decreases with increasing temperature.
                                    62.

-------
Thus,  for nitrogen oxides emitted at relatively high temperature,  as



for example those found in combustion processes, the effect is to  deny



the availability of N2
-------
      What these considerations tell us is simply that absorption




process which rely on N2O4 must be discounted in favor of absorption




in which the active species  is N2O3.  In addition, stack gases that are




mainly composed of NO will have  to be adjusted to an average composition




corresponding to N2O3 (viz. a =  0. 5) principally by adding NO2 and not




by relying on  the oxidation of NO by O2 in the stack gas.  This,  then, is




the major reason for almost exclusively examining absorption processes for




NO  at concentrations corresponding to N2 03.






      There is an additional unfortunate effect associated with the need to




add NO? to a stack gas effluent consisting mainly of NO so that the mixture




to be scrubbed is essentially N0Oo.  To illustrate  this,  suppose we have  a
                             Z  o



stack gas with lOOOppm of NO that we wish to scrub.  We add enough NO2




(lOOOppm) to form  lOOOppm of N2Qo and then scrub with,  say,  90% efficiency.




The scrubber effluent will have lOOppm of NO and  lOOppm of NO0 and in
                                                              &



terms of the original lOOOppm of NO we will have reduced the NO  content
                                                              .X.



by only 80%.   In order to achieve  90% reduction of the original NO we would




have to scrub with an efficiency of 95%.  Thus,  the need to add NO2  to the




stock gas for  the purpose of producing a scrubbable mixture  requires that




the scrubber operate at an efficiency considerably greater than would be




necessary based upon the original NOX  content of the stack gas.







      If there  is anything at all fortunate about the need to add NO0 in order
                                                               £



to produce a scrubbable mixture,  it is that the NO2 is readily available
                                     64.

-------
from those processes which regenerate the scrubbing materials, as we




shall see later.







     Chappell (5) tentatively concludes from his experimental study that




alkaline slurries and solutions (calcium, magnesium, zinc,  sodium hydrox-




ides) are not very efficient for NOx wet scrubbing.  Table 2  shows that




less than 30% NO2 was removed and generally smaller percsntage  of NO




was scrubbed out of NOX mixtures that never exceeded a  total concentration




of 0. 08% by volume.  In another study, First and Viles (6) found higher




scrubbing efficiencies, greater than 90%, with water as the scrubbing




medium and virtually no change in absorption efficiency upon adding caustic




to the scrubbing liquor.  The theoretical study by Lowell  (4) produced some




evidence that  CaO was  a potentially suitable  scrubbing medium for NOX




removal from stack gases.






      Although the First and Viles study  (see Table 3) was conducted at




considerably higher concentration levels than in Chappell's work, the




effect of concentration  on scrubbing efficiency does not by itself serve  to




explain the rather large discrepancy in NOx removal capacity between




the two works.  One possible contribution to the difference in scrubbing




efficiency could be due to mechanical differences between the two sets  of




experiments.   Chappell used a simple fritted  bubbler to introduce the NOX




bearing gas into a static absorbing medium while First used a sixteen




stage gas absorber in which the scrubbing medium was sprayed over the




gas mixture in each stage.  The effect of scrubber design on absorption
                                    65.

-------
capacity has been investigated by Strom (8) and Peters (9) in laboratory




scale equipment.  Their studies show that absorption efficiency is clearly.




dependent upon scrubber type.  Until  the effect of contacting efficiency




due to equipment variation is carefully controlled, experimental studies




will continue to be difficult to reconcile.  Drawing conclusions from results




reported in the general literature (Table 1) is also complicated by the




effect of different contacting devices.







      One further result can be drawn from the data presented.  Although




it was suggested  that at low NC)  concentrations the predominant absorption
                              A.



mechanism should involve N2 03, the data do not bear this out.  In the




First and Viles study, when  the inlet NO approximates an N2Og  mixture





(runs 1 and 4 for which a [n -  0. 5) then the  NO and NO2 absorbed  are




approximately  equal, leading to calculated values of  a removed  ~ °° 5<




However, when there is more NO2 than NO in the inlet gas (runs 2 and 3




for which a  -n  > 0. 5) then more NO2 is absorbed than is associated with




NO to form N2 Og. This is shown in the calculated values of   a removed




for runs 2 and  3 for which a removed >  °-5-  Apparently NO2 absorption




(possibly as N2O4) proceeds even at low concentrations of NO2 for which it




was previously assumed little absorption would occur.  This effect is even




more  pronounced  in the Chappell data (Table  2) where for a total of 10




absorptions in alkaline solution each involving  a -m^. 0. 5, 7 runs resulted




in more NO2 absorbed than NO suggesting that another species in addition




to N2O3 was being absorbed.
                                    66.

-------
      Notwithstanding the difficulty in interpreting NOX absorption data,




 it would be appropriate to examine two complete system descriptions for




 NOX  removal from stack gases by wet scrubbing processes.  The first of




 these is attributed to Schmidt and Weinrotter (10) who describe NO
                                                                X.



 scrubbing for a nitric acid plant using aqueous suspensions  of Mg(OH)2




 or MgCC>3.  A schematic representation of the process is  shown in




 Figure 3.







      The scrubbing process essentially produces Mg(NO2)2 according to




 the reaction:





             N2O3 + Mg(OH)2    =   Mg(NO2)2   +  H2O              (8)







 Because the alkaline solution will not react with NO alone, the tail gas




 effluent which is fed to the scrubber must be adjusted  to N2O^ by the addi-




 tion of NO2. The NO2  used to balance the  NO in the tail gas is produced by





 oxidation of NO which is formed by the thermal decomposition of Mg(NO2)2




 after leaving the scrubber.  The decomposer typically operates at temper-




 atures in excess of 300°F and 4 atm. to produce a mixture of Mg (OH)2 and




 Mg(N03)2:





       3Mg(N02)2 + 2H20 =  2Mg(OH)2 + Mg(NO3)2 + 4 NO             (9)







The NO produced in this decomposition stage is oxidized to NO2,part of which





is used to blend with NOx in the tail gas to produce N2O3 and the balance




returned to the HNO3 plant.   The recovery of Mg(OH)2 is completed in the




precipitator ( ammoniator)  where, by the  addition of NH3, the Mg (NO3)2
                                    67.

-------
is" converted to NH4NO3 and







      Mg(N03)2 + 2NH3 + 2H2O  = 2NH4NO3 + Mg(OH)2               (10)







By combining equations (8) - (10), Mg(OH)2 and all its intermediates




can be eliminated:





            3N2°3 + 2NH3 + H2°  =  2NH4NO3 + 4NO                  
-------
(calculated as  N2O3).  For a typical 120 ton/day nitric acid plant dis-





charging tail gas at the rate of 80, 000 SCFM (85°F, 92 psig) containing





0. 125% N2O3,  then about 37 tons /day of NH4NO3 must be disposed of.





If the NOX in the tail gas is essentially NO and all the NO from the de-





composer  is oxidized to NO2 and returned to the nitric acid plant (except





for enough NO2 to  adjust the  tail gas to N2O3) then  equation (11) shows





that 2/3 of 37 or about 25 tons/day of NH4NO3 are produced.  In either




case a very large amount of low value (about $48 /ton) waste product must




be accounted for.








      There are no readily available cost data for the control of NOV
                                                                 .A.




emissions  in nitric acid plant tail gas.  However,  Bartok (10) has analyzed





the sensitivity of control costs  for NO  recovery as NH^NOs for a  !0°° M




gas  - fired power plant using the Mg (OH)0 scrubbing system.  His results,
                                        Cl



Figure  4,  shows that the scrubbing system annual operating cost would be




completely paid for if a net credit back to the plant of about $60 /ton could





be realized by the  sale of the waste
      Some experimental data on NO  removal from combustion gases using
                                   A.



wet scrubbing with MgO is available from pilot studies  using this scrubbing





medium for controlling particulate and SO2 emissions from the combustion





of pulverized coal (19).  The observed efficiency for SO2 and particulate





removal was better than 99% for both materials in a floating bed absorber





and 95 - 98% for the pollutants in a venturi scrubber.  The limited data
                                    69.

-------
 taken for NO  removal showed that no reduction could be measured for
            A.



 NOX as produced in the combustion furnace.  Assuming this was due to




 the predominance of NO in the combustion flue gas, NO2 was  injected




 into the gas upstream of the scrubbers.   Under these conditions  the total




 NOV at the scrubber exit increased  significantly while simultaneously pro-
   j£



 ducing large quantities of magnesium sulfate in the scrubbing liquor.




 These results can be explained by oxidation reactions between NO2 and




 SOX in the gas and  liquid phases.  In the gas phase NO2 will oxidize SO2




 to SO3 which will produce 112804 upon being absorbed in the MgO slurry.




 In the liquid phase,  NO  will oxidize sulfite ions to sulfate. In both cases
                      L*



 the NO2 will be  reduced to NO and pass out of the scrubber unabsorbed.




 A tentative solution to this problem was recommended in terms of a two-




 step process in  which SO0 is first removed by MgO scrubbing followed
                        &



 by NO2 injection to produce N2O3 with NO in the combustion gas and




 absorption in a Mg(OH)  slurry.
                      £






      Despite the lack of satisfactory operating information for full-scale




 or pilot demonstration sized units, the basic concepts developed in the




 Mg(OH)2 scrubbing system appear sound.  Particularly attractive is the




 flexibility enjoyed with respect to scrubbing materials; other  substances




 such as carbonates of magnesium and calcium,  could readily  substitute





 for Mg(OH)2 depending on availability and price.  The precipitation step,





 shown here to produce NH4NO3 from NH3,  could use as substitutes alka-




line CO2 to produce NaNOs or other alkaline salts.  There is  also a useful
                                  70.

-------
 flexibility in the operation of the process,  particularly with respect to an



 ability to treat stack gases having a large variation in NOX composition and



 a possibility of removing a slip  stream of NO2 from the oxidizer which




 could be recycled to the source  plant to produce more nitric acid.







 Wet Scrubbing With Sulfuric Acid



      The second scrubbing system to be described employs sulfuric acid



 as the scrubbing medium.  Interest in sulfuric acid as wet scrubbing



 material  is based on the well known chemistry of the chamber sulfuric



 acid process and the important catalytic role  played by nitrogen oxides in



 sulfuric acid production.





      The process sequence starts with the oxidation of sulfur to SC>2 and



 ammonia  to NC>2.  Both gases are brought  together in a tower where the



 NO2  oxidizes the SC>2 to 803 while itself being reduced to NO.  If the SO2



 oxidation  by NO2 is carried  out  in the presence of water and excess air,



 sulfuric acid is formed from the SO3 and the NO is reoxidized to NOg.





      Most of the acid was produced in large lead-lined chambers where



 sufficient time was allowed for SO  oxidation  by NO2 and NO oxidation by



 air,  and enough water sprayed over the gases to allow the withdrawal of



 62-66% H0SO,,,  so-called chamber acid. NO  and NO  leaving the chambers
         A  (±                                      A


were absorbed in strong H2SO4,  about 80%, and at low temperatures, below



 100°F to produce nitrosyl  sulfuric acid.
                                   71.

-------
      NO + N02 (or N203) + 2H2SO4 = 2NOHSO4 + H2O               (14)





 which is soluble in sulfuric acid.  Reaction (14) is reversible and



 nitrosyl sulfuric acid will decompose if diluted below 80% H2SO4 and



 heated.  This is accomplished by pumping the strong H2SO4 containing



 nitrosyl sulfuric acid back to the nead of the process, where it is contacted



 with hot SO2 from the sulfur burner and diluted with chamber acid.  The



 regenerated NO and NO  gases in contact with SO  are  lead to the chambers
                       £                        <£


 where the  process  is repeated.





      An adaptation of the lead chamber process for the simultaneous



 control of  SO2 and  NOX in flue gases from stationary combustion sources



 has been developed by Tyco Laboratories under EPA sponsorship (11).



 Although the Tyco process essentially employs the same basic chemistry



 as the lead chamber process,  significant changes in some methods were



 required.  These are explained below for the basic Tyco flowsheet shown



 in Figure 5.





      1.  Nitrogen oxides, with an average composition of N?O3, are



 recovered  in the chamber process by absorption in concentrated  (80%),



 cold (about 60 F),  sulfuric acid by forming nitrosyl sulfuric acid which



 is soluble in cold,  strong acid. In the Tyco  process, nitrogen oxides with



an average adjusted composition as  N2O3, is stripped from stack gases by



absorption in concentrated (80%),  hot (about  250°F) sulfuric acid by forming



nitrosyl sulfuric acid which is soluble in hot, strong acid.  The substitu-
                                   72.

-------
tion of hot for cold sulfuric acid is due to the fact that cold concentrated




H2SO4 readily absorbs water vapor.  If the water vapor present in flue




gases was absorbed along with NOX then the acid would become too dilute




to efficiently absorb NOX.  By maintaining the scrubber exit at a tempera-




ture high  enough to produce a partial pressure of water equal  to its partial




pressure  in the  flue gas,  there  can be no net absorption of water vapor




and no dilution of the scrubber acid0 The scrubbed flue gas would carry




with it as  much  water vapor as  was produced during combustion.  Tyco




reports that N^Oo scrubbing efficiencies of 98%  are generally possible




even though the  absorption takes place at a much higher temperature than




was considered  optimal in the lead chamber process.







      2.    In the lead chamber process,  the nitrosyl sulfuric acid was




decomposed to form NO by dilution and heating,  the heat being largely




supplied by the hot SO2 gases from the sulfur burners.  This  route is not




available  in a stack gas cleaning operation and to provide the  heat necessary




for a thermal regeneration is prohibitive.  As an alternate, Tyco developed




a catalytic oxidation process operating at scrubber  temperature which simul




taneously  denitrates the sulfuric acid of nitrosyl sulfuric acid and oxidizes




the NO released to NO2.  Tyco  reports 99% recovery of N2O3 with their




catalytic process of the nitrogen oxides  absorbed during  high  temperature




scrubbing.
                                    73.

-------
      3.    The NO released from nitrosyl sulfuric acid in the lead




 chamber process was mixed with air and SO2, the former to oxidize NO




 to NO9  and the latter to be oxidized by the NO2 formed by air oxidations
      ^



 of NO.   In the Tyco process,  some of the NO2 produced in the catalytic




 decomposition of the nitrosyl sulfuric acid is injected into the stack gas




 coming directly from the combustion source.  Sufficient NO2 is blended




 with the stack gas to oxidize the  SO2  present to SO3 and to form the equi-




 valent of N2O3 which is  then absorbed along with SO3,  in  the high tempera-




 ture scrubber.  Part of  the NO2  from the catalytic unit is absorbed with




 water to produce nitric acid and  NO which is air oxidized  and blended with




 flue gas.  The net result of the overall Tyco process is the production of




 sulfuric and nitric acids from stack gases containing NOX and SO2.  An




 economic estimate of the costs for an 800 MW power plant burning coal




 containing  3. 5% sulfur showed that 27, 700 tons of HNOo (100%) and 252, 000
                                                    O



 tons of  H2SO. (100%) could be produced.  Capital  investment for control




 equipment  would  be about $12  million and the process would be economically




 self-supporting if HNO3  could be sold for $40 /ton (100%) and H2SO4 sold



 for $10/ton (100%).






      Bartok (10) points  out that the need to oxidize SO9 with NO0 from
                                                    &        £



 recycled NO adds a huge burden to the absorption process just to reduce




 the  NO in the flue gas to  a reasonable level.   For example, if the flue gas




contains 2000 ppm of SO2 and  1000 ppm of NO then 5000 ppm of recycle




N02 are required to oxidize the SO2 and produce the  N2O3 necessary for
                                  74.

-------
absorption.  Therefore, if a 90% reduction of the original NOX in the flue




gas is required then the scrubber must operate at 98. 3%  efficiency on the




6000 ppm of N2O3 actually delivered to the scrubber inlet.  Bartok's




estimate of control  costs for a  1000 MW coal-fired power plant controlled




by the Tyco process is shown in Figure 6.









         WET SCRUBBING WITH COMPLEX FORMING SUBSTANCES







      We have examined thus far, scrubbing systems using aqueous solvents




which combine with nitrogen oxides and convert them to nitrates, nitrites,




and nitric acid.  A completely different class of scrubbing agents, which are




potential solvents for nitrogen oxides,  are those which form complexes




with NO and  NO2 of the .charge  transfer or coordination type.







      Nitric  oxide,  which  contains an odd election,  is particularly sus-




ceptible to forming  complexes with many metals and salts due to an easy




ability to  lose or share its odd  election.   In general, such complexes,




generally classified as nitrosyl compounds, are readily decomposed,




sometimes simply by heat, to the original reactants without serious degrad-




ation.   Two principal types of  products are formed.  The first containing




ionic  species such as NOCl(cationic compounds) or species  such as NaNO




(anionic compounds) both formed by simple election transfer.  The second




group is composed of coordination compounds in which a  pair of elections




is donated by NO to  a central metal atom.  Examples of complex nitrosyls
                                   75.

-------
include (1) CuNOXg  formed by contacting NO with concentrated copper


chloride or bromide solutions, (2) [CoNO(NH3)5 ] X2 formed by replacing


NH3 in hexammine cobaltous salts [Co(NH3)g] X2, where X is either a


halide or sulfate and  (3) Co(CO)3 NO formed by replacing CO in cobalt


tetracarbonyl Co(CO)4_  The formation of nitrosyl complexes is described


in detail by Moeller (13).
      Among the most important complexes formed are coordination

                                +n

compounds of the type M(NO)X Ay    where M  = Fe, Co,  Ni, Mn and



A =C1,  SO4.  Ganz and Mamon (14, 15) have critically  studied one of


these complexes, that formed by contacting NO with Fe SO^ solutions.


The solubility of NO in FeSO^ solutions appears to be the greatest of all


the possible metal chlorides and sulfates belonging to this group.  NO


solubility in 20% FeSO4 is of the order  of 1200 times the solubility of NO
in water at 20 C.
      Although this system  is considered a classical example of the



complexing ability of NO, it is less than an ideal choice for a practical



scrubbing system.   The presence of oxygen along with NO in the gas to



be cleaned will readily oxidize the solute to ferric sulfate which does not



complex with NO.  Also, any NO2 present that will dissolve  in water and



form HN03 will oxidize the FeSO4 to Fe2 
-------
In-the absence of oxidizers such as O2 and HNO3, ferrous sulfate can be




regenerated many times.







      In addition to  inorganic salts, .some purely organic materials and




organometallics have been suggested  as possible candidates for complex




formation with NO.  Mauryand Nahill  (16) have patented the use of such




materials as dime thy Iformamide,  dimethylether and dioxane for this




purpose.  They find that complex formation can occur in nonaqueous solu-




tions of the complexing material but that the presence of controlled amounts




of water increases the overall absorptive capacity of the system.  The




suggested reason for this  is that the organic complexing material acts as




a transfer agent, first complexing the NO and then releasing NO to  the




water phase where nitrous acid is  formed.  Other materials reported by




Maury and  Nahill as having a significantly increased absorptive capacity




for nitrogen oxides compared to water includes tri - n-butylphosphate, tri-




phenylphosphate, and dimethylsulfoxide.







      Although there are some obvious objections to using low molecular




weight organic complexing agents with vapor pressures that are sufficiently




high to  cause significant losses of  the complexing material at normal  stack




temperatures,  there has been at least one practical use for such materials




involving NOX recovery. In 1970,  Nash (17) reported the use of 2-methoxy-




phenol (quaiacol) as an absorption  agent for use in sampling bubblers  for




collecting NO9 in ambient  air.  Collection efficiencies as high as  99% were
                                    77.

-------
reported for quaiacol-NaOH absorbers compared with about 70% when




NaOH was used alone.  Atmospheric ozone and SO2 oxidize quaiacol easily




and interfere with the absorption process which makes the material in-




appropriate for cleaning stack gases, but the use in air quality sampling




systems is satisfactory.







      At the  Cooper Union, we have been examining as yet another complexing




agent which shows promise as an NO  scrubbing material.  In 1962,




Silvestroni and Ceciarelli (18) reported that aqueous solutions of cobalto-




dihistidine were efficient NO absorbers. Although the testing of this




•material has been exploratory only, some tentative results are available.




Figure  7 shows the solubility of NO and NOg in cobaltodihistidine solution




at 20 C.  Only measurements at very high NO   pressures have been made
                                            .X.



and the solubility behavior at low  pressures is  by extrapolation and is sketchy




and tentative.  Of considerable interest, though, is the indication of a




possible affinity of the solution for both NO and NO9 absorption, a  valuable
                                                 

  • -------
    is-an example of an NOx recovery process for a 200 ton/day nitric acid
    
    
    
    
    plant.  The tail gas from the nitric acid plant is passed through an
    
    
    
    
    absorption column where the NOx gases are absorbed, the lean gas is
    
    
    
    
    
    then returned to the plant for power recovery and discharged to the atmos-
    
    
    
    
    phere.  NOx  picked up by the absorber scrubbing Hquor is stripped
    
    
    
    
    and returned to the nitric acid plant while the regenerated  scrubbing
    
    
    
    
    liquor is recycled  to the absorption tower.  Assuming an arbitrary 88%
    
    
    
    
    reduction of NOX in the plant tail gas,  the recovered gases can produce an
    
    
    
    
    additional 5 million Ibs. of 40°Be acid per year for a net value of about
    
    
    
    
    $85, 000 after deducting the cost of manufacturing this amount of acid
    
    
    
    
    ($30/ton) from the selling price  ($83/ton, 100% basis).  No attempt has
    
    
    
    
    been made to  estimate the cost of recovery system with the spare infor-
    
    
    
    
    mation now available.  A comparable flow sheet for NO  recovery from
                                                         .X.
    
    
    
    combustion systems has not been attempted since there is  no specific data
    
    
    
    
    on the effect of SO2 in  the stack  gas on the NG>X process.
    
    
    
    
    
    
    
    
    
    
    Conclusion
    
    
    
    
          This review has attempted to indicate the current status of wet
    
    
    
    
    scrubbing as a possible control method for the removal of nitrogen oxides
    
    
    
    
    from stationary sources.  In so  doing, it  has been necessary to highlight
    
    
    
    
    the field,  selecting from among  many possible scrubbing systems which
    
    
    
    
    have been suggested  as having potential for NOX control.  We have purpose
    
    
    
    
    ly avoided the problem of absorption dynamics and  the related area of
                                      79.
    

    -------
    absorption equipment in favor of describing the physical chemistry of ab-
    
    
    
    
    sorptive processes for NOX> illustrating where possible the application
    
    
    
    
    of specific chemical systems to stack cleaning processes. It is hoped
    
    
    
    
    that the examples used have served to show the rich potential for NOX
    
    
    
    
    control that can result by the resourcefull combination of sound chemical
    
    
    
    
    and engineering principals.
    
    
    
    
    
    
    
          From the material presented, it should be quite evident that  the
    
    
    
    
    desired goal of NO  control by wet scrubbing has not been achieved as yet.
                      Ji
    
    
    
    In come cases proposed systems await demonstrations of their theoretical
    
    
    
    
    ability to provide adequate control; in other cases more research is apparent
    
    
    
    
    ly necessary to determine  the potential for control.  In either case it is
    
    
    
    
    hoped that wet scrubbing methods will continue to be explored as a possible
    
    
    
    
    method for controlling NOX emissions.
                                       80.
    

    -------
                             ACKNOWLEDGEMENT
          The author wishes to express his appreciation to Mr. Stuart Roth,
    
    
    
    
    Air Programs Division, Region II,  U. S. Environmental Protection
    
    
    
    
    Agency for his assistance and guidance with EPA publications and research
    
    
    
    
    activities and to Mr. Robert  Meier for his thorough effort in surveying
    
    
    
    
    and organizing the technical literature for this report and particularly for
    
    
    
    
    his patience  and contributions to our many discussions on environmental
    
    
    
    
    control.
                                          81.
    

    -------
     References
     1.    Partington, J.R. , " A Text-Book of Inorganic Chemistry",
          Macmillan and Co. ,  Limited, London, 1939.
    
     2.    Yost, Don M. and Horace Russell,  Jr.,  "Systematic Inorganic
          Chemistry", Prentice-Hall,  Inc., New York, 1946.
     3.    Hoftyzer- P. J. andF.J.G.  Kwanten, "Absorption of Nitrous
          Gases",  Chapter 5,  Part B, p. 164 in "Processes for Air Pollution
          Control", G. Nonhebel (ed. ),  CRC Press,  Cleveland,  Ohio 1972.
    
     4.    Lowell,  Philip S. , et. al.,  "A Theoretical Study of NOX Absorption
          Using Aqueous Alkaline and Dry Sorbents", Radian Corporation,
          NTIS PB 211035, December 31, 1971.
    
     50    Chappell, Gilford A. ,  "Development of the Aqueous  Processes for
          Removing NOX from Flue Gases", Esso Research and Engineering,
          NTIS, PB 212858, September  1972.
    
     6.    First, Melvin W. and Frederick J0 Viles,  Jr. ,  "Cleaning of
          Stack Gases Containing High Concentrations of Nitrogen Oxides",
          JAPCA,  2_3 (No.3), 122 (1971).
    
     7.    Morrison,  M0E., Rinker,  R.  G,  and Corcoran,  W. H. ,  "Rate
          and Mechanism of Gas-Phase  Oxidation of  Parts-per-million
          Concentrations of Nitric Oxide",  Ind. Eng. Chem. Fundamentals,
          5_ ,  1975 (1966).
    
     8.    Strom,  S, S.,  "The Absorption of NO2 with a Venturi Scrubber",
          Paper 67C, 67th  Annual Meeting A. I. Ch. E. , Atlanta, Georgia,
          February 1970.
    
     9.    Peters,  Max S. ,  Chemical Engineering, 200 (May,  1955).
    
    10.    Bartok,  W, et. al. ,  "Systems Study of  Nitrogen Oxide Control
          Methods for Stationary Sources - Vol. II, Esso Research and
          Engineering, NTIS PB 192789 , November 20, 1969.
                                       82.
    

    -------
    11.   Walitt, Arthur and Arnold Gruber,  "A Process for the Manufacture
         of Sulfuric and Nitric Acids from Waste Flue Gases", Second
         International Clean Air Congress, Englund, H. M. and W. T. Beery
         (ed. ), Academic Press, New York, 1971.
    
    12.   Schmidt,  A. and F. Weinrotter, U. S. Patent 3,034,853, May 15,
         1962.
    
    13.   Moeller,  T. " Inorganic Chemistry",  John Wiley and Sons,
         New York,  1952.
    
    14.   Ganz, S. N.  and L. I. Mamon,  "Absorption of Nitric Oxide by
         Ferrous Sulfate",  Zhur.  Priklad.  Khun.,  26^, 1005 (1953).
    
    15.   Ganz, S.  N. and L. I.  Mamon, "Kinetics of Film Absorption of
         Nitric Oxide by Ferrous Sulfate",  Zhur. Priklad.  Khim. ,  30,
         391 (1957).
    
    16.   Maury, L.G. and Nahill,  G.F., U.S.  Patent 3,044,344,  July 17,
          1962.
    
    17.   Nash, T. ,  "An Efficient Absorbing Reagent for Nitrogen Dioxide",
         Atmospheric Environment, £,_661  (1970).
    
    18.   Silvestroni, Paolo and Laura Ceciarelli,  La Ricerca Scientifica,
         2,  121 (1962).
    
    19.   Downs, W. , et. al.,  "Magnesia Base Wet Scrubbing of Pulverized
          Coal Generated Flue Gas  - Pilot Demonstration",  Babcock and
          Wilcox Company, NTIS PB-198074, 28 September 1970.
                                       83.
    

    -------
                                                                                TABLE  1
    
                                                                            NOx  ABSORPTION STUDIES
    oo
    -p-
    (SELECTED LITERATURE - 1962/1972)
    (1)
    REF.
    1
    2
    3
    4
    5
    6
    7
    8
    TITLE: PRODUCT:
    . HYDROXIDES (MOH)
    Abs. of NOx by NaN02 3
    vibrating layers
    of NaOH
    Abs. of NOx with Ca(N02,3)2
    milk of lime
    Abs. of NOx in NH4 N02.3
    aqueous NH3
    CARBONATES (MCOs)
    Abs. of NOx by NaN02,3
    vibrating layers
    of NaCOs
    Abs. of NOx (w. NaN02,3
    Na2C03) ..in
    large scale plate
    col-
    Abs. of NOx by Na2 NaN02»3
    C03 solutions ...
    Abs. of NOx with Ca(No2,3)2
    limestone suspension
    Abs. of NOx in Ca(N02,3)2
    solid CaC03
    EQUIPMENT/ NOx FEED a
    METHOD CONC. % (N02/NOX) n (%)
    Vibrating
    film
    Mech.
    Scru bber
    Closed coni- 0.3-8 — 70-54
    cal abs. with
    sprayer.
    Vibrating .55-1.8 .2-. 6 87-98
    film
    12-perf. tray .3 .5 75
    scrubber
    2 packed cols.
    ceramic rings
    15 tray bubble
    cap-foam layer
    
    ABSORBENT EFFICIENCY, ^ AS FUNCTION
    CONC. OF SYSTEM PARAMETERS:
    "n- max., f f [N02 or 02]
    0 30 g/1
    f[ f f LCaC03]
    or TCfoanO.
    Salt recovered
    by H20 rinse.
         (1)  References for Table  1 will be  found  at  end  of  Table.
                                                                                                                                                Continued  ,,,
    

    -------
                                                                    TABLE  1  (continued)
    00
    REF.
    9
    10
    11
    12
    13
    14
    15
    16
    TITLE:
    Abs. of NOx by
    (NH4)2C03 solutions
    (Abs. of) .. NOx
    with (NH4)2 C03 &
    NH4HC03
    Scrubber for
    selective removal
    of N02 fr. NOx
    (w. Ag.2 C03+PTFE)
    ALKALINE SOLNS.
    Abs. of NOx in solns
    of NaOH & Na2C03
    Alkaline abs. of
    NOx
    Removal of NOx . . .
    . by H202 solutions
    NOx absorption in
    alkaline solns.
    SALTS
    Abs. of .. NOx by
    aq. solns. of KMn04
    PRODUCT:
    NH4N02.3
    NH4N02.3
    HN03
    Ag N03
    NaN02,3
    MN02.3
    -™o2,3
    MN02.3
    KN03
    EQUIPMENT/ NOx FEED . a ABSORBENT EFFICIENCY, n AS FUNCTION
    METHOD CONC. % (N02/NOX) n U) CONC. OF SYSTEM PARAMETERS :
    Column « .5 10-1'5 -- ?if as [N203]f , LAbsbt.Jf
    4.5-10.4 .5 31-67 .2-1.7 M
    8. 1 ppm 99
    Vibrating
    Layer
    Column w. .6-1.2 .3-. 6 to 90*° 110 g/1. Tjf as <¥.t, [N0x]4 , T|
    centrifugal
    sprayer
    Foam forming .7-1.0 .2 90-93*** 1-3 g/1 ^tas[NO]t , T| ,
    apparatus (absorbt.)t
    .5-2.5 ^.5 ^(NaOH) > ^ (NaCOs)
    Foam absorber ~ — 92 * ^.5
    2 perf. plates
                                                                                                                                               COMMENTS:
                                                                                                                                              HC03/C03 varied
                                                                                                                                              fr. 0-1
                                                                                                                                              100% Ad2 C03 or
                                                                                                                                              PTFE +110-70%)
                                                                                                                                              Abs. "complete"
    
    
                                                                                                                                              10" ^ T ^ 40*
                                                                                                                                              Oxidation rate
                                                                                                                                              increases w.
                                                                                                                                              KMn04 addition &
                                                                                                                                              as [H202]|  to 5%
                                                                                                                                              * At optimum
                                                                                                                                              conditions.
                                                                                                                                            Continued ...
    

    -------
                                                                    TABLE  1  (continued)
    oo
    REF.
     17
     18
         19
         20
                 TITLE:
    
                 Abs. of NOx by
                 solns. of NaC03
                 in presence of
                 recycled NaN02,3
    
                 Abs. of NOx by
                 solns. of
                 di substituted
                 ammonium phosphate
    PRODUCT:
    »a»2,3
    EQUIPMENT/
    METHOD
    
    NOx FEED
    CONC. %
    
    (N02/NOX)
    
    ,„. ABSORBENT
    ^/a) CONC.
    [Na2C03]
    <3 g/1
    [Salts] =
    34-36%
    EFFICIENCY, '
    OF SYSTEM
    ''I fas [N20;
    and as [N02~,
    n AS FUNCTION
    PARAMETERS
    N03]f*
    COMMENTS:
    * *? (NOf)
    NH4N02,3
    phosphates
    & H3P04
    Abs. of NOx by       NH4N03
    NH4N03 solns. &      & HN03 *
    HN03
                 Removal  of NO fr.
                 industrial gases
                 (w.  various salts*)
                                                               3-10%      .5-. 9
                                                    8-stage model   8-10       .9-. 95
                                                                                      ^97
                                                                                     40% H3P04     Tjtas  [N0x]t  , °
    

    -------
                            Reference for Table 1
     1.    Mirev, D. et.  al. , "Absorption of Nitrogen Oxides by Vibrating
          Layers of NaOH Solutions",  Compt.  Rend.  Acad. Bulgare Sci.
          _14 , 259-62 (1961).  CA 56:66a.
    
     2.    Ganz,  S. N. , et. al. ,  "Absorption of Nitrogen Oxides with Milk
          of Lime in Mechanical Absorbers", Khim.  i Khim. Tekhnol.  5,
          No.  1,  155-9 (1962).  CA 57: 3245e.                         ~
    
     3.    Pawlikowski, Stanislow  Aniol, et.  al., "Absorption of Nitrogen
          Oxides in Aqueous Ammonia in Nozzles. I".   Przemysl Chem.
          42 (9),  490-4 (1963).   CA 60: 6501c.
    
     4.    Mirev, D. , et. al., "Absorption of Nitrogen  Oxides  in a Vibrating
          Layer of Sodium Carbonate Solution III",  Compt.  Rend.  Acad.
          Bulgare Sci. _14, 345-8 (1961).  CA 56: 5795c .
    
     5.    Kuz'minykh, I. N. , "Absorption of Nitric Oxide from Nitrogenous Exhaust
          Gases in Large-scale Plate Columns I. ", Tr. Mosk. Khim. -Tekhnol.
          List.  1961, No. 33, 43-7. CA57:2022h.
    
     6.    Krustev,  I. , "Absorption of Nitrogen Oxides  by Sodium Carbonate
          Solutions Under Industrial Conditions", Khim. Ind. (Sofia)  1968,
          (4),  147-51.  CA 69:  78766y.
    
     7.    Rodionov,  A. I. , et. al. , "Absorption of Nitrogen Oxides With A
          Suspension of Limestone", Tr. Mosk. Khim.  - Tekhnol. Inst.
          1963  (40), 74-7.  CA  61: 6463a.
    
     8.    Blasiak, Eugeniusz and  Jariczek, Witold, Pol.  Patent 43, 284
          "Absorption  of Nitrogen Oxides from Dilute Mixtures, Aug. 30,
          1960.  CA57: 7075f.
    
     9.    Atroshchenko,  V.I. and B.  N. Gushchin, "Kinetics of Absorption of
          Nitrogen Oxides by Ammonium Carbonate Solution",  Zh. Prikl.
          Khim. _39 (12),  2627-33  (1966). CA 66: 57341d.
    
    10.    Gushchin,  B. N. and  V. I. Stroshchenko,  "Relative Reaction Rat es
          for Nitrogen Oxides with Ammonium Carbonate Compounds in Solution
          and in the Gaseous Phase", Izv.  Vyssh. Ucheb.,  Zaved, Khim.
          Tekhnol.  10(3),  314-18(1967).  CA 67:  76605c.
                                         87.
    

    -------
     11.   Neti,  Radhkrishna, et. al., "Scrubber for the Selective Removal
          of Nitrogen Dioxide from a Nitrogen oxide containing Gas Flow",
          Ger. Patent 2,209,877, Sep. 1972.  CA 77: 156038u.
    
     12.   Mirev, D.,  et. al.  "Absorption of Nitrogen Oxides in Solutions of
          NaOH and Na2CO3" Izv. Inst. Obshcha Neorg. Khun. , Org.  Khim.,
          Bulgare Akad. Nauk. _8, 83-101 (1961).  CA 57: 5752h.
    
     13.   Ganz, S. N.  and I.E. Kuznetsov,  "Alkali Absorption of Nitrogen
          Oxides in a Column Provided with a Centrifugal Sprayer", Zh. Prikl.
          Khim. _36_(8),  1693-7 (1963). CA bO: 7694h.
    
     14.   Kuznetsov, I.E., S. N. Ganz and N.  P0 Shpak,  "Removal of Nitrogen
          Oxides irom Exhaust Gases by Aqueous Hydrogen Peroxide Solutions"
          Dneproopetrovsk. Khim.  -Tekhnol. Inst.  1968, No, 13, 77-81.
          CA. 71: 73740s.
    
     15.   Krustev, Iv. "Kinetics and Mechanism of Absorption of Nitrogen
          Oxides in Alkaline Solutions. 2, "  Izv. Otd. Khim.  Nauki, Bulg.
          Akad. Nauk. 1970, 3 (2),  203-13.  CA 74: 43869.
    
     16.   Kuznetsov, I.E., S. N. Ganz and R.  S. Sokol.,  "Absorption of
          Weakly Acidic Nitrogen Oxides  by Aqueous Solutions of  Potassium
          Permanganate",  Dnepropetrovsk. Khim.  -Tekhnol, Inst. , 1967 ,
          No.  8.,  162-5. CA 70: 152046.
    
     17.   Krustev, Inv. , "Absorption of Nitrogen Oxides by Solutions Contain-
          ing Sodium Carbonate,  Sodium Nitrite, and Sodium  Nitrate",  Izv.
          Otd. Khim. Nauki., Bulg. Akad.  Nauk.  1968, 1 (1) 109-23.
          CA 70: 107834x.
    18.   Pozin,  M.E. ,  et. al.,  "Absorption of Nitrogen Oxides by Solutions of
          Disubstituted Ammonium Phosphate", Massoobmeiinye Protsessy
          Khim.  Tekhnol.  1969, No.  4,  174. CA 73: 37016t.
    
    19.   Pozin,  M.E.,  et. al. ,  "Absorption of Nitrogen Oxides by
          Ammonium Nitrate Solutions.  Ill", Massoobmennye Protsessy
          Khim.  Tekhnol.  1969, No.  4,  174-6.  CA 73: 37025v.
    
    20.   Bresan, Giancarlo and  Salvatore Gafa, "Removal of Nitric Oxide
          from Industrial Gases", U.S.  Patent 3, 635, 657, January 18,  1972.
                                     88.
    

    -------
                                                                                 TABLE  2
                                                                           NOx SOLUBILITY STUDIES
    oo
    (FROM G.A. CHAPPELL, "DEVELOPMENT OF THE AQUEOUS PROCESSES FOR REMOVING N(
    NTIS PB212858 - 1972)
    (1) NO & N02
    CLASS
    WATER
    ABSORBENT
    Water
    ALKALINE NaOH
    
    
    
    
    
    
    
    
    
    AMINE
    
    
    
    ACID
    
    SALT/
    ESTER
    
    
    NaOH
    NaOH
    NaOH
    Ca(OH) si.
    Ca(OH)2 sat.
    Mg (OH)2 si.
    Mg (OH)2 sat.
    ZnO si.
    ZnO sat.
    NH40H
    2-aminoethanol
    ii 11
    i i
    H2S04
    HOAC
    NH4C1
    NH40AC
    NH40 Citrate
    NaOAc
    COMP. pH 6.6
    
                                    ?7 f f (Na, Ca, Mg ..) @ const.  pH
                                                                                                                                        -F [2AE]
          (1)   Unless otherwise specified: T = "Std.  125°F. (120-130), aQ  = 0.5 (.46 -  .54),
          (2)   NO was generated during NO, absorption
          (3)   The "comparison" list shows results for different conditions in Chappell's  report
    [NOX]
    650 - 800 ppm.
    continued
    

    -------
    CLASS    ABSORBENT
    SULFITES'S BISULFITES
    COMP.
    % ABSORBED
                               NO
           NO 2
    Na2S03
    Na2S03/NaOH
    Na2S03
    NH4HS03
    + NH4S04
    NaS
    CaS03 si.
    CaS03 si.
    CaSOs si.
    CaSOs si.
    Sat. 0.5
    Sat/5N
    2.5 m
    1.0
    3.6 m
    1.9
    2.3 m 12
    8 g/l ?
    I 7'2
    I 8'° 1
    T 12 '
    /Std. 21
    12
    16
    15
    24
    Low
    33
    35
    35
    " 32*48
    100
    100
    100
    100
    100
    100
    60
    66
    60
    100*4
       TABLE  2  (CONT.)
    NOx SOLUBILITY STUDIES
    
        •   NO & N02	
    
               COMPARISON
    % ABSORBED
                                                  NO
                                          NO 2
                                                                                  Same 0 70-85"F.     27     TOO
                                                                                  Same @cxe=.6,855 ppm 18     TOO
    COMMENTS
    
    
      1? = f IT)
           Lso3=j
                                                                                  Same 00^=1 .,370 ppm
                                                                                    100
                                                                                                                                            continued
    

    -------
                                                                          TABLE 2  (Cont.)
                                                                       NOx SOLUBILITY STUDIES
    NO, N02 & S02
    [NOx]
    860
    690
    700
    950
    700
    680
    830
    680
    700
    650
    650
    650
    490
    725
    a.
    1
    1
    1
    0.47
    1
    1
    1
    1
    1
    1
    1
    1
    0
    0.45
    -Jh
    9.1/7.2
    9.4/3.7
    5.9/5.9
    6.3/6.3
    11.2/6.5
    11.2/6.4
    8.7/7.8
    9.3/7.9
    9.3/6.3
    7.5/6.2
    7.2/6.3
    _
    -
    % ABSORBED
    NO N02
    TOO
    - 100+45*
    94
    22 100
    63
    56
    58
    56
    63
    46
    46
    6 100
    0
    8 37
    
    (S02)
    (TOO)
    (TOO)
    83
    (97)
    (100)
    (100)
    (100)
    (100)
    (100)
    MOO)
    (100)
    (95)
    '(70)
    (70)
    ALTERNATE CONDITION % ABSORBED
    ABSORBENT [NOx] Ou LS02J pH NO N02 (S02)
    CaS03sl.8g/l 330 1.0 500 7.6/5.0 - 60 92
    
    
    Ca(OH)2 si. 10 g/1 740 1 0 11.2/6.6 19
    Mg(OH)2 si. 680 0.5 0 8.9 6 23
    ZnO si. 723 0.5 0 7.5 7 16
    
    Na2S 2.3 m 700 0.5 - 12 Low 100
    Urea 3.8 m 480 0 - 3
    ABSORBENT
    SULFITES
    
    CaS03 si. 25 g/1
    MgS03 5 g/1
    NH4HS03 2m     7
    (NH4)2S04 0.5 m j
    (NH4)2S03 Mixt. **
    ALKALINE
    
    Ca(OH)2 si. 15 g/1
                18 g/1
    
    Mg(OH)2 si. 7.4 g/1
    Mg(OH)2 si. 14 g/1
    
    ZnO si. 10 g/1
    
    CaCOs si. 10 g/1
    CaC03 si.  4 g/1
    MISCELLANEOUS
         2.1 m
    Urea 3.8 m
    Urea 3.8 m
    
    *   MgSOs depleted  by  02  in flue gas?
    **  Mixt. =  11.2% NH4HS03, 14.6% (NH4)2S03,  16.6%  (NH4)2 S04  in  H20.
    

    -------
                                TABLE 3
    
                    NOX  Absorption In NaOH Solutions
                        Data of First & Viles (Ref. 6)
    SCRUBBER  INLET           -              SCRUBBER EFFICIENCY,  % REMOVED
    Run NO %NOX
    1 0.
    2 9.
    3 5.
    4 32.
    845
    60
    63
    8
    %NO2
    0.460
    5.91
    4.87
    19.0
    %NO
    0. 385
    3.69
    0.76
    13.8
    a in
    0.54
    0.615
    0.865
    0.58
    NCL NO2
    90. 3
    90. 3
    92.6
    97. 3
    94.
    94.
    96.
    98.
    4
    9
    0
    1
    NO
    85.
    82.
    70.
    96.
    a Removed
    4
    B
    2
    1
    0.
    0.
    0.
    0.
    57
    65
    90
    58
    

    -------
            NO,
            NO   I	«*.
    GAS-BULK
    GAS-FILM
    INTERFACE
    LIQUID-FILM
                                                   FIGURE 1
                                                NOX ABSORPTION MODEL
                                                                                                      HN0^2NOH20
    LIQUID-BULK
                                                   (REF. 3)
    

    -------
                               FIGURE 2
     Alkaline Scrubbing
    
    
             NO  + MOH
     N2O4 (or 2 NO2) + MOH
             N2 O3 +2 MOH
         salting out of NO
         MNO2 + MNO3 +
         2 MNO,
               H20
    Carbonate Scrubbing
    
            NO +  M2CO3
    N2O4 (or 2NO2)  + M2CO<
    
            N2  + M2CO3
                                     salting out of NO
    MNO
                                     2MN02
                  MNO
                                                      CO
     * where M  = Na  , K ,
     +    +2
    ,• i Ca  .  etc.
    ** solubility of NO is reduced below that of NO in water by the
         presence of the soluble hydroxide or carbonate.
                                   94.
    

    -------
                                        FIGURE 3
    
                                 Mg(OH)2 SCRUBBING PROCESS
    STACK GAS
      FROM
    HN03 PLANT
                  TREATED
                  STACK
                  GAS
        TO HN03
        PLANT     <-
    NO,
                        0
                        X
                        I
                        D
                        I
                        Z
                        E
                        R
                        t
                       AIR
                              NO
                                          SCRUBBER
                                       DECOMPOSER
              Mg(OH)2
            Mg(NOs)2
                                         NH3
                                                              (RECYCLE)
                                                               Mg(N02)2
                                                              (RECYCLE)
                                                         AMMONIATOR
                                                         Mg(OH)2
                                                               NH4N03
                                                               SOLUTION
                                                   HZ)
                                                              PRECIPITATED
                                                              Mg(OH)2
                                               95.
    

    -------
                                   FIGURE 4
    
                        SENSITIVITY OF CONTROL COSTS
    
                            TO BY-PRODUCT CREDIT
    
                     SINGLE SCRUBBER Mg (OH)2  PROCESS
    
                        WITH THERMAL DECOMPOSITION
    
                     (1000 MW GAS-FIRED  POWER PLANT )
    
                                   (REF. 10)
       2400
       2000
    o  1600
    o
    o
    •ea-
    
    
    H  1200
    
    O
    O
    I
        80°
        400
        400
                                                                          50
                                                                          25
                _ C2S_T_ _
    
                 PROFIT
                                                                               O
                                              P
                                              W
                                              >
                                              0
    
                                              w
                                              K
                                               x
                                              O
                                                                               O
                     10
                             20
    30
    40
    50
    60
    70
                  NO3  PRODUCT CREDIT  $/TON NET BACK TO PLANT
                                          96.
    

    -------
                                FIGURE 5
    
                        TYCO CATALYTIC  CHAMBER  PROCESS
                      Gas  to  Stack
                        250"F'.
                        7% H20
                      150  ppm NOX
         Gas
         NO
         N02
         S02
    Reactor
    
          Air - NO
    Flue Gas
    0.3% S02
    0.6% NOX
                            H20
                        HNOs
                        Absorber
          Product
          HNOs
                                                       High
                                                    Temperature
                                                     Scrubber
    Gas
                      H2S04
                                              Air
                           Product
                           H2S04
    
                                                                          .80% H2S04
                                                   80%
                                                   H2S04
                                                   +
                                                   HNS05
                                              Catalytic
                                              Stripper
                                                                80%
                                                                H2S04
                                        97.
    

    -------
       2400
    o  1200
    O
    u
        800
        400
                          FIGURE  6
    
    
              SENSITIVITY OF CONTROL COSTS
    
                  TO BY-PRODUCT CREDITS
    
              SULFURIC ACID SCRUBBING SYSTEM
    
             (1000 MW  COAL-FIRED POWER PLANT)
    
    
                          (REF. 10)
       2000  _
       1600  —
         0   L_
        400
    ($/Ton Net Back Product
    
     Credit for 80%  H2SO4)
                                                              CNJ
                                                             O
                                                              ra
                                                              cd
                                 w
                                 K
                                                             O
                                                     100
           HNO3  PRODUCT CREDIT,  $/TON NET BACK TO PLANT
                               98.
    

    -------
                                   FIGURE 7
       800-
       600
    CD
    
    
    E
    LJ
    V}
    V)
    Ul
    I-
    o:
    400
       200
         /
        /
        /
        /
       / /
      / /
      //
     //
     / /
    //
    '/
       SOLUBILITY OF NO & NOx IN
       AQUEOUS COBALTODIHISTIDINE
       (3 20°C.
    
       9 gms CoCl? + 31 gms Histidine
       per liter solution
    
         $ =   N02
    
         @ =   NO
               I
        0
             i
             //
           0
                    4
                      8
    12
    16
    20
                             Gm NOx / Gm SOLUTION
    
                                       99.
    

    -------
    o
    o
             SCRUBBED  TAIL GAS
           85°F., 92 psig
           [NOxJ = 350 ppm
           CN2J  = 96.2 %
           [02J  = 3.1 %
           [H20] = 0.7 %
           RECYCLE TO
               PROCESS
           85°F., 92 psig
           NOx  10 %
           H20  90 %
                                WASTE HEAT BOILER
      L>
    EXPANDER
      TURBINE
    J
    c
    
    
    STRIPPER
    
    • ft*
    TFAM ""
    
    
    
    
    
    
    
    
    
    ^ 	 •— J
    / 	 0
    J
    te
    
    
    xr^x
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    V V
    ^^ -^x
    COOLER
    
    
    
    
    S^
    
    ABSORBER
    f/\ ^ \^
    .j.
    TAIL GAS FROM
    HMO? TOWER
    
    
    
    
    
    fti
    
    
    85UF., 92 psig
    [NOx] = 3 %
    [N?] = 96.1
    [02] = 3.0 %
    [H20] = 0.6 %
    
    
    
    
    
                                           ABSORDER - STRIPPER RECOVERY SYSTEM
    

    -------
                 EPA-View  of  Stationary and Mobile  NO -Source Control
                                        by
                                    Conrad Simon
    
    
    Introduction
    
         EPA's view   of  the NO   problem has undergone considerable change
    
    since the passage of the  Clean  Air Act of  1970.  A complete description
    
    of EPA's policy reflecting  this change will be forthcoming within the
    
    next month or so.  The most  significant effect of this change in outlook
    
    was reflected in  Administrator  Ruckelshaus' testimony before the Senate
    
    Sub-committee on  Air and  Water  Pollution during the week of April 16, 1973.
    
    The Administrator asked the  Senate Committee  to rescind the statutory re-
    
    quirement under Section 202  (b)  of the Clean  Air Act that light duty
    
    vehicles and engines manufactured during and  after the 1976 model year achieve
    
    a reduction of at least 90 per  cent from the  average emissions of oxides of
    
    nitrogen actually measured  from light duty vehicles manufactured during the
    
    1971 model year.   The  1971 emissions averaged 3.5 grams per mile and the 1976
    
    standard is 0.4 grams  per mile  . The Administrator has also requested that
    
    Congress grant him the power under section 202 (a) of the Act to set standards
    
    as he sees fit.   If this  were granted it is likely that a standard would be
    
    set significantly higher  than the 0.4 grams per mile currently in effect for
    
    1976.  Applicable  standards  expressed in terms of the 1975 Federal CVS procedure
    
    are given in Table I.
    
         EPA is particularly  concerned about changing the 1976 emissions standards
    
    for oxides of nitrogen in motor vehicles because it no longer appears necessary
    
    for the achievement of national ambient air quality standards and because it
    
    represents a most  difficult emissions control goal to achieve.  In fact it has
    
    been determined that attempts to achieve the  emission standard for oxides of
    
    nitrogen using a  catalyst system could jeopardize achievement of the CO and
    
    hydrocarbon standards while imposing a sizable fuel penalty of about 15%.  If
    
    given this authority,  the Administrator would not change the standard immediately,
                                         101.
    

    -------
    but would wait until new health effects data were obtained and evaluated.  The
    
    
    
    
    standard would then be set at a level that is adequate to protect against health
    
    
    
    
    effects and to provide for maintenance of the national ambient air quality standard
    
    
    
    
    by minimizing the impact of growth on existing ambient concentrations.  In
    
    
    
    
    setting new emission limitations to maintain ambient air quality standards
    
    
    
    
    for nitrogen dioxide (N02) EPA would seek to obtain a balance in the requirements
    
    
    
    
    imposed on stationary sources and mobile sources.
    
    
    
    
         This revision in EPA's evaluation of the N02 problem is primarily the
    
    
    
    
    result of the Agency1 re-examination of the air quality measurement method
    
    
    
    
    used in various presentations to establish the status of the N0? pollution
    
    
    
    
    problem.  Some of these presentations were made before Congress prior to the
    
    
    
    
    passage of the Clean Air Act of 1970 and some constituted the air quality data
    
    
    
    
    used in the development of States' implementation plans.  EPA is now convinced
    
    
    
    
    that important portions of the data based used in these two activities were
    
    
    
    
    unreliable.  It should be stated clearly at this point that a national ambient
    
    
    
    
    air quality standard has been established specifically for nitrogen dioxide
    
    
    
    
    (N0?).  No air quality standard has been established, nor is contemplated, for
    
    
    
    
    nitric oxide (NO).   Emission standards and control strategy, on the other hand,
    
    
    
    
    have been expressed in terms of oxides of nitrogen in recognition of the fact
    
    
    
    
    that the major source of N0_ associated with significant ambient concentrations
    
    
    
    
    is NO contained in the atmosphere as a result of emissions from combustion
    
    
    
    
    sources.  Only a small and relatively insignificant amount of N09 is produced
    
    
    
    
    directly and emitted by these sources.
                                        102.
    

    -------
    Air Quality Data Base
    
    
    
    
         For several years various investigators have argued that discrepancies
    
    
    
    
    existed hetween air quality measurements of NO  made with the Jacobs-Hochheiser
    
    
    
    
    procedure used in the National Air Surveillance Network  (NASN) and air quality
    
    
    
    
    data obtained through various other  sampling techniques, particularly the
    
    
    
    
    Saltzman method.  This argument climaxed on April 30, 1971, when EPA promulgated
    
    
    
    
    the National Ambient Air Quality  Standards.  The standard analytical methodology
    
    
    
    
    to be used to measure the ambient concentrations of each of the six pollutants for
    
    
    
    
    which national standards were being  set was also stipulated.  These were referred
    
    
    
    
    to as "reference methods".  The reference method for NO  was the Jacobs-Hochheiser
    
    
    
    
    method.  The regulation establishing this "reference method" would have to meet
    
    
    
    
    certain criteria in order to demonstrate their equivalence to the reference method.
    
    
    
    
    These criteria will be published  in  the near future.
    
    
    
    
         When States attempted to develop  implementation plans in 1971, they found
    
    
    
    
    that air quality data for carbon monoxide, nitrogen dioxide and photochemical
    
    
    
    
    oxidants were generally sparse.   In  response to this need EPA in the summer of 1971
    
    
    
    
    conducted a special study of air  quality levels for these pollutants in those
    
    
    
    
    urban areas where data were sparse.   This Summer Study using the Jacobs-Hochheiser
    
    
    
    
    method became the source of a considerable amount of the ambient NO  data used by
    
    
    
    
    the States to develop their implementation plans.
    
    
    
    
         Based on the results of the  Summer Study and various other data available
    
    
    
    
    from the NASN stations, state and local agency networks, it was determined by the
    
    
    
    
    end of 1971 that 47 Air Quality Control Regions (AQCR) in 29 states should be class-
    
    
    
    
    ified Priority I for N0.
                                      103.
    

    -------
    Priority classifications of either I or III are assigned to AQCR's as a means of
    
    
    
    indicating the degree of control of emissions of oxides of nitrogen that may be
    
    
    
    necessary to provide for the achievement of the NO  standard.  Priority I is
    
    
    
    assigned to those regions where air quality levels have equalled or exceeded
    
    
    
    110 ug/m3 or 0.06 ppm as an annual arithmetic mean.  Those with lower concentrations
    
    
    
    are assigned a Priority III classification.  The national ambient air quality
    
    
                                3
    
    standard was set at 100 ug/m  or 0.05 ppm as an annual arithmetic mean.
    
    
    
         In order to determine the control strategy necessary to meet air quality
    
    
    
    standards for NO  in these regions, Federal regulations required the following
    
    
    
    procedures:
    
    
    
         1.  Assume certain emission reductions that will result from the Federal new
    
    
    
    motor vehicle emission standards.
    
    
    
         2.  Take credit for the impact of any transportation control measures
    
    
    
    taken to achieve carbon monoxide and photochemical oxidant standards.
    
    
    
         3.  Impose emission limitations attainable with reasonably available control
    
    
    
    technology on stationary sources.
    
    
    
         4.  If 1, 2, and 3 do not achieve sufficient NO  emission reduction of
                                                        X
    
    
    hydrocarbons as may be possible by reasonably available control technology.
    
    
    
    (Hydrocarons are associated with the conversion of NO to NO  in the atmosphere).
    
    
    
         EPA has determined that certain control technology for existing sources of
    
    
    
    oxides of nitrogen is reasonably available for combustion sources and nitric acid
    
    
    
    plants.  The achievable emissions limitations are listed in Table II and compared
    
    
    
    with performance standards for new sources.  In 1972 some States adopted
    
    
    
    regulations containing emissions limitations similar to these.  Where States failed
    
    
    
    to adopt such emissions limitations EPA proposed them.  In deference to the
    
    
    
    existing controversy over the accuracy of air quality data for NO. EPA refrained
    
    
    
    from making final promulgations.
                                         104.
    

    -------
    Measurement  techniques  -  Prior  to  1970  there  was  one  basic  technique used
    
    
    for the measurement  of  ambient  concentrations of  NO and  NO  .   This  technique
    
    
    involved the Griess-Ilosvay  reaction  for  N02  which was utilized  in  the
    
    
    Saltzman and the Jacobs-Hochheiser methods.
    
    
         Other techniques not amenable to ambient sampling were gas  chromatography,
    
    
    long-path infra-red  spectroscopy and  electrochemical  oxidation or reduction.
    
    
    Over the past 6 years EPA has fostered  the development of the  gas phase
    
    
    chemiluminescence  technique  for application to air quality  monitoring.
    
    
         The Griess-Saltzman  method was deemed the most suitable manual method
    
    
    for measurement of NO-  in the atmosphere  by the Standardization  Advisory
    
    
    Committee, National  Air Pollution  Control Administration and the Intersociety
    
    
    Committee on Manual  Methods  for Ambient Air Sampling  and Analysis.  In this
    
    
    procedure NO  containing  air is bubbled through the Griess-Saltzman reagent
    
    
    for a period of up to 30  minutes.   The  Saltzman reagent  consists of, among
    
    
    other things, sulfanilic  acid and  N-(l-naphthly)-ethylenediamine dihydrochloride.
    
    
    NO. reacts with these compounds to  form a diazo dye with a  characteristic color
    
    
    whose intensity is proportional to  the amount  of NO   absorbed.   This method is
    
                                           3
    usable for NO  in air of  40 - 1500  ug/m   (0.02  to 0.75 ppm).   Using sodium
    
    
    nitrite as a calibration  standard,  Saltzman found that 0.72 mole of nitrite
    
    
    produced about the same color as 1 mole of NO   gas.   The method  is fairly specific
    
    
    for NO  and no significant interferences  commonly occur.  SO   for example shows
    
    
    significant interference  only at concentrations of about 30 times that of N0_.
    
    
         The problem with the field application of  this method  lies  in the need to
    
    
    limit absorption time to about 30 minutes and  the analysis  time  to one hour
    
    
    after color development.  In order  to develop a procedure to meet the need for
    
    
    sampling over periods as long as 24 hours, the  Jacobs-Hochheiser method was
    
    
    developed.
                                     105.
    

    -------
         In an EPA modification of this procedure sodium hydroxide (.IN NaOH)
    
    
    
    
    is used as an absorbing reagent.  Sulfanilamide replaces the sulfanilic acid
    
    
    
    
    of the Saltzman reagent and the acid is phosphoric acid rather than acetic.
    
    
    
    
    Since some of the NO  absorbed goes towards the formation of sodium nitrate,
    
    
    
    
    on the average only 0.63 mole of nitrite was required to produce the same color
    
    
    
    
    as 1 mole of NO  gas.  This stoichiometric factor has been the source of
    
    
    
    
    considerable controversy in recent years with values reportedly ranging from
    
    
    
    
    0.5 to 1.00 (for the equivalent quantity of nitrite ion).
    
    
    
    
         All NASN measurements have used an NO  - Nitrite stoichiometirc factor of
    
    
    
    
    1. 0.  That is to say, only nitrites and not nitrate ions were assumed to be
    
    
    
    
    formed during the absorption of the gas from the ambient air.
    
    
    
    
         It was also determined that the absorption efficiency of  NO  was highly
    
    
    
    
    variable with NO  concentration and was also dependent on the  amount of NO
    
    
    
    
    present in the air.  On the basis of detailed studies made under laboratory
    
    
    
    
    conditions the NASN system was assumed to have an efficiency of approximately
    
    
    
    
    35%.
    
    
    
    
         The Saltizman method was also adopted to continuous analyzers and was used
    
    
    
    
    in EPA CAMP stations as well as stations operated by various State and local
    
    
    
    
    agencies.  Most of these analyzers were also used for measurement of NO by
    
    
    
    
    first oxidizing all NO to NO  and subjecting it to the process of diazotization.
    
    
    
    
    The oxidation process reportedly has an efficiency ranging from 40% to 100%
    
    
    
    
    (using potassium permanganate or dichromate or chromium trioxide).
    
    
    
    
         Differences in the air quality data obtained from the Saltzman and Jacobs-
    
    
    
    
    ^ochheiser methods at the same sites led EPA to make a careful examination of the
    
    
    
    
    reliability of its reference method and the accuracy of the air quality data
    
    
    
    
    used for priority classification.
                                    106.
    

    -------
    A report on the first phase of the EPA investigations and the findings was
    
    
    made by Hauser and Shy in October 1972.
    
    
    
         In this first phase, a test of the efficiency of the reference method
    
    
    
    was made using nitrogen dioxide - air mixtures of varying concentrations
    
    
    
    generated by the use of NC>2 permeation tubes.  For each of the test atmospheres
    
    
    
    generated, at least five simultaneous sample were collected and analyzed.  The
    
    
    
    results shown in Figure 1 indicate that the collection efficiency of the
    
    
    
    reference method varies nonlinearly with NO  concentration from about 15% at 740
    
    
        33                                         ^
    ug/m  to about 70% at 20-30 ug/m .  For an ambient level of about 120 ug/m  the
    
    
    
    previously assumed efficiency of 35% is valid.  Above that level, the use of a
    
    
    
    35% efficiency will underestimate the actual concentrations in ambient air.  At
    
    
    
    lower ambient concentrations, the reference method will result in erroneously
    
    
    
    high estimates of concentration if a 35% efficiency is assumed.
    
    
    
         The effect of the presence of nitric oxides (NO) on the reverence method
    
    
    
    was also examined.  The response of this method to various concentrations of
    
    
    
    NO. with and without NO is given in Table III.  A comparison of the expected and
    
    
    
    apparent N0_ recovered shows positive interference from NO.
    
    
    
         Since these problems with efficiency and interference were related to the
    
    
    
    absorbing solution, EPA examined several alternate solutions for possible
    
    
    
    adoption.   Three different absorbing reagents were tested in the NASN network
    
    
    
    and two were rejected because of physical problems even though collection
    
    
    
    efficiencies were higher and more consistent than those of the Jacobs-Hochheiser
    
    
    
    Method.  Hauser,  T. and Shy, C:   Position Paper:  NO  Measurement.  Environmental
                                                        X
    
    
    Science and Technology,  October 1972.
                                    107.
    

    -------
    The sodium arsenite - sodium hydroxide reagent has been found most satisfactory
    
    
    by EPA.  This reagent (the method is called the Christie method) has been
    
    
    tested at all 200 stations of the NASN network since December 1971, and has
    
    
    recently replaced the Jacobs-Hochheiser method in routine sampling.
    
    
         In the second phase of this investigation beginning August 1972, cherailu-
    
    
    minescent equipment has been installed at selected urban sites in 41 of the
    
    
    AQCR's classified Priority I and at all CAMP stations where instruments using
    
    
    the continuous Saltzman methods were located.
    
    
         The results of these measurements show that of the 47 AQCR's previously
    
    
    classified as Priority I only two, Los Angeles and Chicago, will definitely
    
    
    retain their former classification.  Three other regions, Salt Lake City, Denver
    
    
    and New York, are marginal.  The remaining 42 AQCR's will all be reclassified
    
    
    Priority III.
    
    
         Chemiluminescent analysers will also be maintained in 17 of the 47 AQCR's
    
                                                                      3
    where annual average concentrations are expected to exceed 75 ug/m .  Multiple
    
    
    sites will be located in New York, Los Angeles ,and Chicago.  The chemiluminescence
    
    
    method has been adapted to measure both NO and NO .  In this technique NO
    
    
    undergoes a gas phase reaction with ozone to produce NO  in an excited State.
    
    
    The intensity of light emission from the reactor is proportional to the NO
    
    
    content of the sample.  To measure concentrations of NO , a catalyst is first
    
    
    used to convert NO  to NO.
    
    
    The NO thus produced is then reacted with Ozone.
    
    
    Effects of findings on Control Strategies for Stationary Sources in Implementation
    Plans
    
         With the exception of Los Angeles and Chicago no control strategy for
    
    
    existing stationary sources over and above that which had been fully implemented
    
    
    by the end of 1972 is required to maintain the NO  standard in the absence of
    
    
    further growth.  Where EPA has proposed emission limitations on sources of
    
    
    combustion for implementation plan purposes, these proposed regulations will be
    
    
    withdrawn.
    
    
                                      108.
    

    -------
    Where states and  localities have acted  to promulgate regulations imposing
    
    
    emission limitations  on  these  sources,  EPA will work with the agencies in
    
    
    rolling back these  actions as  desired.  There are some cases however in
    
    
    which states and  localities have developed emissions standards prior to any
    
    
    EPA requirement for the  purpose of meeting a local air quality standard or
    
    
    to reduce the potential  for the production of photochemical oxidants.  In
    
    
    these cases the matter remains one for  local consideration.  New York City
    
    
    is one of the latter.  In the  case of nitric acid plants or any other sources
    
    
    of N02 as a primary emission,  existing  control regulations will be required
    
    to stand.
    
    
         In terms of  control strategy to achieve the national air quality standard,
    
    
    it is estimated that  Chicago will be able to show achievement by 1975 through
    
    
    the following measures:
    
    
         1.  Reductions attributable to the Federal new motor vehicle program
    
    
             through  1974.
    
    
         2.  Reductions obtained through the conversion in fuel from the use of
    
    
             coal to  gas  and oil.
    
    
         3.  Reduction in the formation of  NO  in the atmosphere through the
    
    
             control  of hydrocarbons.
    
    
         A.  Reductions obtained from the transportation control plan developed by
    
    
             Chicago  to acheive CO and hydrocarbon standards.
    
                                                                     3
         Los Angeles was  estimated to have  an annual mean of 180 ug/m .  The State
    
    
    of California already requires control  of NO  from motor vehicles.  EPA
    
    
    believes that transportation control programs developed to meet the CO and
    
    
    photochemical oxidant standard existing stationary source controls and the
    
    
    vehicle emission control program will permit the achievement of the NO- standard
    
    
    in this AQCR.
                                   109.
    

    -------
    Control Strategy to Provide for Maintenance and Growth
    
    
    
         The requirement that implementation plans provide for the maintenance
    
    
    
    of standards into the far future imposes a need to develop control strategies
    
    
    
    which will adequately handle additional emissions associated with future
    
    
    
    growth.  It is a very difficult problem to determine where the most cost
    
    
    
    effective reductions can be made whether in stationary or mobile sources,
    
    
    
    in high level or low level emissions.
    
    
    
         An examination of the estimated emissions of NO  in the U.S. in Tables 4,
                                                        X
    
    
    5 shows that more than 99% of the total emissions are derived from combustion
    
    
    
    sources - more than 90% comes from the combustion of fossil fuels.
    
    
    
         In the relatively high temperature conditions accompanying the combustion
    
    
    
    of fossil fuels and wastes, only a comparatively small amount of N0» is formed.
    
    
    
    In fact, the rate of oxidation of NO to NO  decreases with increasing temperature.
    
    
    
    It is estimated that at temperatures of 2000 F the NO  formed is only 0.5% of
    
    
    
    the NO  .  At the low concentrations of NO normally found in the atmosphere
          X
                        3
    (l.Oppm or 1200 ug/m ) the subsequent oxidation of NO to N0_ by direct reaction
    
    
    
    with oxygen in ambient air occurs very slowly.  The rate of conversion is pro-
    
    
    
    portional to the square of the NO concentration leading to rapidly decreasing
    
    
    
    conversion with dilution.  The primary mechanism for the formation of NO
    
    
    
    therefore, is the photochemical process involving reactive hydrocarbons.
    
    
    
         As a result of this, the diurnal variations in NO, N09 and ozone (or total
    
    
    
    oxidants) show the following pattern (Figure 2):  An NO peak at approximately
    
    
    
    7 am; an NO  peak at approximately 10 am and an ozone/ oxidant peak around 12
    
    
    
    noon to 3 pm.  The pattern is similar for both normal and stagnation conditions.
    
    
    
    Just as in the case of hydrocarbons and photochemical oxidants, it is the 6-9
    
    
    
    am emissions of NO which are most important in the production of the N00 maximum.
    
    
    
    There are also indications that the conversion from NO to NO  is a function of
    
    
    
    emission rate, meteorologically determined diffusion rate, and the reaction
                                     110.
    

    -------
    rate, which is determined by  chemistry  and meteorology.  Because of the lag
    
    
    
    time tin peak N02 -production,  total  NO  emissions  are perhaps more important
    
    
    
    than individual point  emissions  from specific  sources  in determining peak
    
    
    
    N02 production.  In built up  areas like New York  City, where daytime wind
    
    
    
    speeds near the surface  are considerably  lower than those at rooftop, the
    
    
    
    rate of dilution of emissions  from motor  vehicles  is less rapid than the rate
    
    
    
    of dilution of emissions from rooftop and elevated sources.  Since 40% of
    
    
    
    N0x emissions are estimated to be derived from mobile  sources, these sources
    
    
    
    must remain a primary  source  for emission reduction in future control strategy.
    
    
    
    This would hold true even in New York City where  it has been estimated that
    
    
    
    93,000 out of 332,000  tons of  NO  (or 28%) are produced by mobile sources.
    
    
    
    However, based on air  quality  measurements of  SO   (for which a reliable
    
    
    
    inventory is available)  it appears likely that emissions of NO  from stationary
                                                                  X
    
    
    sources in New York City are considerable overestimated and that mobile sources
    
    
    
    play a greater role in NO/NO   emissions in New York City than currently estimated
                                X
    
    
         EPA considers the existing schedule  up through 1974 for control of NO
    
    
    
    emissions from mobile sources  through the Federal  new motor vehicle program
    
    
    
    essential for the maintenance  of standards.  Additional limitations are also
    
    
    
    needed for 1976 and later model year  cars, but not as stringent limitations
    
    
    
    as the 90% reduction required  by the  Clean Air Act.  The actual needs
    
    
    
    have not yet been determined.
    
    
    
         To assist in maintaining  air quality standards, EPA will retain standards
    
    
    
    of performance for NO  emissions from new and  modified stationary sources.
                         X
    
    
    In addition, to this,  future performance  standards for sources of significant
    
    
    
    NO  emissions  will include NO   emissions  limitations that reflect best available
      x                          x
    
    
    control technology.
                                     111.
    

    -------
     Effect of New Data on the National Standard
    
    
    
         These  findings concerning the reliability of the Jacob-Hochheiser method
    
    
    
     are important in respect to the determination of the national primary standard
    
    
    
    
     for NO  in which the Chattanooga School Children Study played an important role.
    
    
    
    
     The results obtained in that study with a modification of the reference method
    
    
    
    
     were compared with measurements made by the U.S. Army using continuous monitors
    
    
    
    
     based on the Saltzman method.  These monitors, running simultaneously within
    
    
    
    
     0.4 miles of the air monitoring sites established in the EPA study area, showed
    
    
    
    
     values of 0.099ppm and 0.087 ppm in the period November 1968 through April 1969
    
    
    
    
     as compared with a value of 0.109 ppm at the EPA study site.  In addition, the
    
    
    
     individual measurements were adjusted on the basis of the true collection efficiency
    
    
    
     curve.  The new estimates for the critical Chattanooga site showed an increase of
    
    
    
     11.3% in exposure.  Moreover, the U.S. Army collected NO data in the area which
    
    
    
     demonstrated that the NO/NO- ratio observed at Chattanooga would have had little
    
    
    
     effect on the apparent collection efficiency of N0_.
    
    
    
         These independent measurements of NO  exposures at Chattanooga, the findings
    
    
    
    
     on the efficiency of the Jacobs-Hochheiser method and the low level of possible NO
    
    
    
     interference, clearly indicate that the application of the Jacobs-Hochheiser method
    
    
    
    
     in the circumstances of the Chattanooga study did not significantly effect the choice
    
    
    
    
     of the national air quality standards.  Further health effects studies are being
    
    
    
    
     conducted at CHESS sites using the Saltzman method and are expected to further
    
    
    
    
     substantiate the current standard.  EPA is seeking, within the next 18 to 24 months,
    
    
    
    
     to establish the basis for a short term standard for NO  .
    
    
    
    
    ^.iforcement Standards  - The major emphasis by EPA over the next few years will be
    
    
    
    
    in the area of  standards and implementation plan enforcement.  Federal Standards
    
    
    
    
    for NO  have been promulgated for new motor vehicles only.  Achievement of these
          X
    
    
    emission standards will be determined through extensive Federally observed
    
    
    
    
    certification procedures of vehicle engines.   There is still some question whether
                                       112.
    

    -------
     all vehicles will,  in the future,  be required to achieve the standards in-
    
    
    
    
     dividually  or whether averaging will be allowed.  Certification requirements
    
    
    
    
     include durability  tests for engines to maintain performance over 50,000 miles.
    
    
    
    
     Compliance  by in-use vehicles will be monitored through inspection/maintenance
    
    
    
    
     programs.
    
    
    
    
    
         Only in Chicago and Los Angeles will credit have to be taken for transportation
    
    
    
    
     control measures  to demonstrate achievement of air quality standards.  Enforcement
    
    
    
    
     of State developed  transportation  control plans will be the primary responsibility
    
    
    
    
     of the state.  Where EPA is  bringing direct actions to enforce an approved State
    
    
    
    
     plan or Federally promulgated section of a State plan, the Agency will proceed
    
    
    
    
     under Section 113 (a)  (1)  of the Act.  Under such circumstances EPA is bound to
    
    
    
    
     give a violator 30  days  notice before issuing an order or bringing civil or
    
    
    
    
     criminal action.
    
    
    
    
         EPA could also seek criminal  penalties against an individual violator under
    
    
    
    
     Section 113  (c)  (a)  of the Act. For cases in which there is wide-spread violations
    
    
    
    
     or cases in which a State has failed to enforce its strategies, it is EPA's current
    
    
    
    
     policy to seek compliance by the State under Section 113 (a)  (2)  of the Act.  Under
    
    
    
    
     this section EPA  can issue orders  and bring civil actions against the Director of
    
    
    
    
     state or city agencies charged with implementation of specific strategies.
    
    
    
    
         For cases on which  EPA  might  have to promulgate a plan the Agency will operate
    
    
    
    
     on the theory that  the State is an emission source in that a highway or other
    
    
    
    
     publicly owned property  on which motor vehicles operate is an emission source.  On
    
    
    
    
     this principle, EPA would  enforce  a transportation control regulation through the
    
    
    
    
     issuance of an order to  the  responsible State or City agency rather than directly
    
    
    
    
     against a motorist.   In  these cases no 30 day notice is required.
    
    
    
    
         Enforcement  of  stationary source control requirements for existing sources
    
    
    
    
     required to apply reasonably  available control technology will be the primary
    
    
    
    
     responsibility of the  states.   Sources covered by new source performance standards
    
    
    
    
    will  be regulated by EPA until the  states  obtain delegation of this responsibility
    
    
    
    
    
                                       113.
    

    -------
    and in cases where states have emission limitation regulations will occur at
    
    
    
    
    start-up of new sources and on an ad hoc basis in conjunction with states
    
    
    
    
    thereafter.
                                     114.
    

    -------
    TABLE I
                  FEDERAL LIGHT  DUTY floioR VEHICLE  FJUSSFON STANDARDS
                                          (GM/MI)
    MODEL YEAR           HYDROCARBONS          CARBON  NJNOXIDE     OXIDES OF NITROGEN
    
    PRIOR TO CONTROLS        (8,7)                  (37)                   (3,5)
    3968-1969
    (8,7)
    50-100 CID -
    101-140 CID -
    OVER-140 CID -
    
    
    
    
    
    CALIFORNIA
    fkrioNAL
    
    
    
    10,7
    8,5
    6,8
    /I.I
    4,1
    3,0
    3,0
    3,0
    0,9
    1.5
    Ml
    0,41
    (87)
    66
    57
    43
    28
    28
    28
    28,0
    28,0
    9,0
    15,0
    3,4
    3,4
    1970
    1971                                 4,1        28                     (3,5)
    1972
    1973                                 3,0        28,0                    3,1
    1974                                 3,0        28,0                    3,1
    1975                 CALIFORNIA     0,9         9,0                    2,0
                                                                            3,1
    1976                                 0,41        3,4                    0,4
    1977                                 0,41        3,4                    0,4
          ALL STANDARDS FOR  !!C AND CO ARE EXPRESSED IN TERMS OF THE 1975 FEDERAL
    CVS TEST PROCEDURE,  THE 1975 FEDERAL NOX STANDARD MAS BEEN PRESCRIBED PURSUATIT
    TO SECTION 202  (A) OF THE ACT,
                                                115.
    

    -------
    TABLE   2
              [)QX EMISSION LIMITATIONS REFLECTING AVAILABLE TECHNOLOGY
    
    SOURCE TYPE             EXISTING SOURCE - APPENDIX B            NEW SOURCES - f\!SPS
    FUEL COMBUSTION
    GASEOUS                    0,2 (170)A                              0,20  (170)
    LIQUID                     0,3 (230)A                              0,30  (230)
    SOLID	                              0,70  (525)
    NITRIC ACID PLANTS      5,5 LB PER TON OF 100% ACID PRODUCED       3,0 LB PER TON
                                WOO)                                     (220)
    (  ) = PPM ON A DRY BASIS AT 3% OICYGE1
    A - REPRESENTS ABOUT A 50% REDUCTION IN EMISSIONS FROM UNCONTROLLED FUEL BIOJIKG
        EQUIPMENT,
                                          116.
    

    -------
    TABLE  3
    Effect of M on
    Method for N02
    uq/m3
    NfJ2
    100
    102
    105
    122
    189
    244
    248
    215
    311
    316
    318
    356
    the Refer
    NO
    0
    63
    127
    627
    0
    1205
    1279
    1242
    0
    111
    332
    1060
    •ence
    Ratio
    HO/N02
    0.0
    0.6
    1.2
    5.1
    0.0
    4.9
    5.2
    5.8
    0.0
    0.4
    1.1
    3.0
    Expected
       M02
    
    recovered    recovered
                                                    39
    
    
                                                    39
    
    
                                                    38
    
    
                                                    36
    
    
                                                    29
    
    
                                                    24
    
    
                                                    23
    
    
                                                    26
    
    
                                                   20
    
    
                                                   20
    
    
                                                   20
    
    
                                                   18
                                                               Apparent
                                                                    N02
                   38
    
    
                   38
    
    
                   52
    
    
                   57
    
    
                   29
    
    
                   45
    
    
                   55
    
    
                   50
    
    
                   17
    
    
                  30
    
    
                  33
    
    
                  44
                                 117.
    

    -------
    TABLE
                              NO.
                                x
    U, S,   19G3
    (TONS/YR)
                   SOURCE
                   MOBILE FUEL COMBUSTION 'IOTOR VEHICLES
                   OTHER MDBILE SOURCES
                   STATIONARY FUEL COMBUSTION
                   SOLID HASTE
                   COAL WASTE
                   AGRICULTURAL
                   INDUSTRIAL PROCESSES
                             EMISSIONS
                             7,200,00:1
                             L010,000
                             9,980,nrn
                               556,071
                               190,000
                             L 533,000
                               200,01)
                                                                   20,^9,000
                                           118.
    

    -------
    TABLE
                                                    T./YR.
    SOURCE                  PART.     SO?     CO     1 1C
    TRANSPORTATION           1,0      1,0     77,5   14,7   11,2
    FUEL COMBUSTION
     (STATIONARY)            6,5     26,3      1,0    0,3   10,2
    INDUSTRIAL PRXESSES    13,3      5,5     11,1    5,6    0,2
    SOLID I/ASTE DISPOSAL     0,7      0,1      3,8    1,0    0,2
    MISCELLANEOUS            5,2      0,1      6,5    5,0    0,2
    1971 TOTAL              27,2     33,0     93,9   26,6   22,3
    1970 TOTAL              25,4     33,9    147,2   34,7   22,7
    1969 TOTAL              27.3     33,6    154,0   35,2   22.5
    
         THE MAJOR CHANGES FROM 1959 - 1971 ARE DUE TO REVISED EMISSION FACTORS
    FOR TRANSPORTATION, HC AND CO EMISSIONS AND A CONSIDERABLE REDUCTION  IN
    SOLID WASTE DISPOSED BY INCINERATION,
                                     119.
    

    -------
      c
      1-1
      n>
    .80h
         .70
         .60
       o
    
       M
         .50
        r1
        PI
    |sj   M
    
    ?   £ .40
          .30
          .20
           .10
              PPM .016   .047
                     I	L_
                    30     90
    .080
    1
    150
    .11
    i
    _J 	
    210
    .14
    l
    270
    .18
    1
    330
    .21
    1
    390
    .24
    1
    450
    .27
    1
    510
    .30
    1
    570
    .34
    1
    630
    .37
    1
    690
    .40
    1
    750
                                                      Concentration of NO  Sampled
    

    -------
                      Average Daily 1-Hour Concentrations of Selected
                      Pollutants in Los Angeles, July 19, 1965
                        NO
    2400   0300   0600
    0900    1200    1500
       TIME OF DAY
    1800    2100  2400
    Figure 2
                               121.
    

    -------