United States
Environmental Protection
Agency
Environmental Sciences Research EPA-60Q 2-80086
Laboratory          V1,iy 1 980
Research Triangle Park NC 27711
Research and Development
Impact of Natural
Hydrocarbons on
Air Quality

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                  RESEARCH REPORTING SERIES


Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
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This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

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                                               EPA-600/2-80-086
                                               May 1980
IMPACT OF NATURAL  HYDROCARBONS ON AIR QUALITY
                       by
              Joseph J. Bufalini
    Gas Kinetics and Photochemistry Branch
  Environmental Sciences Research Laboratory
 Research Triangle Park, North Carolina  27711
  ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
      OFFICE OF RESEARCH AND DEVELOPMENT
     U.S. ENVIRONMENTAL PROTECTION AGENCY
 RESEARCH TRIANGLE PARK, NORTH CAROLINA  27711

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                                DISCLAIMER

     This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication.  Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
                                     ii

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                                  ABSTRACT

     The emissions, reactivities, and ozone-forming potential of natural
hydrocarbons are discussed.  A review of the data available on emission
levels for natural hydrocarbons indicates that much more information is
needed in order to quantify the absolute emission levels, because emissions
data do not agree with ambient air measurements.  These ambient air measure-
                                                         Q
ments suggest that the previously-published value of 9 x 10  ton/yr needs to
be lowered to 10 -10  ton/yr.  Emissions may be overpredicted by a factor of
15 to 20, as indicated by back calculations using a simple diffusion tra-
jectory model.
     Isoprene, when compared to the monoterpenes, is much more efficient in
producing ozone through photooxidation in the presence of NO .  This
                                                            X
greater ozone production apparently occurs because of the large amount of
carbon consumed in the formation of aerosols for the monoterpenes.  Since
rural areas have very low levels of NO , vegetative emissions may in fact
                                      X
act as sinks for ozone rather than as sources.  All areas investigated show
very low levels of natural hydrocarbons, suggesting that even if NO  were
                            *                                       X
available, very low levels of ozone would be produced.  Air quality is
thus not found to be significantly affected by vegetative emissions.
                                     iii

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                                 CONTENTS
Abstract	   iii
Figures	    vi
Tables	   vii
Acknowledgement	viii

   1.  Introduction	     1
   2.  Conclusions	     2
   3.  Recommendations	     3
   4.  HC Emissions	     5
   5.  Reactivities of Natural HC's	    17
   6.  Product Formation	    33
   7.  Source-Receptor Relationships	    43

References	    47
Appendix	    53

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                                  FIGURES


Number                                                                Page

  1   Structure of selected natural HC's ............................    10

  2   Loblolly pine forest vertical gradients, 7/18/77, 1035-1100       14
        hr EST [[[

  3   Ozone production as a function of HC/NO  ......................    20
                                             A
  4   Effect of HC/NO  ratio on ozone "wyt"n«" .......... . ............    21

  5   Diurnal variation of HC compounds, Chickatawbut Hill,
        July 18, 1976 ...............................................    23

  6   Total concentration of the C-0 terpene HC's (ppbC) observed
        in the canopy at IBP site. .7 ................................    2*
   7   Total concentration of the C^Q terpene HC's (ppbC) observed
        above the canopy at IBP site	    25

   8   Photooxidation of a-pinene in the presence of NO	    33


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                                  TABLES
Number                                                                Page

  1   Emission rates for selected samples at various locations	    11

  2   Major Emissions from Selected Species	    12

  3   Estimated U.S. and Global Emissions by Lattitude (gC/yr)	    16

  4   Rate constants for selected EC's	     18

  5   Half-life for selected HC's at various ozone concentrations...    27

  6   HC' s found near several cities (ppb V/V)	    28

  7   Summary of biogenic HC concentrations at ambient air	    30

  8   Reactivity and products by Fourier Transform Spectroscopy         35
         (long-path infrared) at 60 min	
                                    vii

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                               ACKNOWLEDGMENT

     I would like to acknowledge the many helpful discussions with Mr.
Robert Amts concerning the natural hydrocarbon issue.  Also, Mr. William
Lonneman was very helpful with the hydrocarbon analyses.  Dr. Marcia Dodge
is also acknowledged for her helpful discussions on modeling as is Dr.
Leslie Hull for the product identification for ozonolysis of terpenes.
     I'm also indebted to Northrop Services for the use of their data on
the smog chamber studies of natural hydrocarbon and to Ms. A. McElroy for
typing the many iterations of this document.
                                    viii

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                                 SECTION 1
                               INTRODUCTION

     The involvement of hydrocarbons  (HC's) in  the formation of photochemical
smog is well documented (1-4).  Also  generally  accepted is that both the
type and the amount of HC are important in the  formation of photochemical
smog.  If ozone is taken as  the indicator for smog formation, at a favorable
hydrocarbon to _NO   ratio    (HC/NO  )  olefins are  found to produce ozone
                 X                X
most quickly,  followed by the substituted aromatics and then the slow-
reacting paraffins.  However, if reduced visibility (or aerosols) is taken
as the photochemical smog indicator,  then the substituted aromatics and
the olefins of higher molecular weight  (C, ) are  the  largest contributors.
     Natural HC's, i.e., isoprene and the monoterpenes, are olefinic com-
pounds that are expected to  produce both ozone  and aerosol.  The question
then arises, can natural HC's be a  significant  source of ozone and visibility
reduction in rural areas?  Also, does vegetation  contribute to photochemical
air pollution  problems that  exist in  most large metropolitan regions?
     In this paper we would  like to critically  review the relevant literature
concerning natural HC's and  their role  in pollution problems observed in
urban and rural areas.  The  HC's to be  considered are the monoterpenes
(CnnH,,) and isoprene  (C_HQ).  Other  natural HC's, such as methane (CH.)
  J.U J.O                 jo                                           *»
and stress-evolved ethene (C«H,), will  not be considered, since CH, is
thought to be  unreactive and C^H, emissions are too small to be significant
(5-7).  The specific topics  covered are:  (1) HC  emissions, (2) reactivities
of natural HC's,  (3) product formation, and  (4) source-receptor relationships.

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                                 SECTION 2
                                CONCLUSIONS

     Although additional information is needed in order to firmly establish
the role of natural HC's in ozone formation, the present data suggest
emissions from vegetation are not likely to have significant effects on
air quality.  All gas-phase HC analyses and carbon aerosol studies suggest
that natural HC's do not exist at sufficiently high concentrations to
affect air quality in either urban or rural areas.  Emissions data do not
agree with ambient air measurements.  Those measurements suggest that the
                                    8                                 6
previously published value of 9 x 10  ton/yr needs to be lowered to 10 -
10  ton/yr.
     Isoprene and the monoterpenes produce ozone when photooxidized in the
presence of NO .  However, they are not efficient ozone producers since
              2t
a large amount of carbon is consumed in the production of aerosols.
Because of the aerosol production, the natural HC's may contribute to
visibility reduction in pristine areas.

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                                 SECTION 3
                                                AT
                              RECOMMENDATIONS

     Additional work in the area of vegetative HC emissions should include:
(1)   Establishment of better emission values.  In-situ vertical profile
     measurements are recommended over enclosure techniques.   The enclosure
     and simulated environmental chamber techniques suffer from possible
     pertubation of the normal environment, which results in unusual
     emissions.  Also, greater understanding and better measurement of the
     biomass factor is needed in the enclosure techniques.
(2)   Better collection and analyses of gases and aerosols in rural and
     urban areas are needed.  These improvements should include a measure
             14  12
     of the C  /C   ratio for the organics, especially for the fine par-
                              14  12
     ticulate fraction.  The C  /C   ratio in living matter is not the same
     as that found in petroleum and coal (8, 9), so one can measure the
     natural versus fossil carbon contribution to the atmosphere by
     determining this ratio.
(3)   Additional smog chamber studies are needed in order to determine the
     ultimate fate of the photooxidation products of natural HC's.  Previous
     studies in this area have met with only limited success and have only
     sketchily defined the mechanism for terpene photooxidation.  Until
     all products are identified, the mechanism will remain this way.
(4)   Modeling exercises are needed in order to establish the importance of
     natural HC's to urban and rural air quality.  Various emission sceneries
     could establish the importance of natural versus anthropogenic emissions.
     These computations would then be compared to observed air quality data
     in order to assess the emission scenerio most compatible with air
     quality data.

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(5)   Finally, we must understand why uninhabited areas (e.g., the Smoky
     Mountains) have reduced visibility.  The data in the area show little
     or no carbon in the fine-particulate fraction but yet reduced visibility
     occurs, and was apparently occurring long before the industrialization
     of America.  Understanding reduced visibility in the mountain areas
     is necessary if we are to understand the role of natural HC's to air
     quality.

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                                 SECTION 4
                                HC EMISSIONS

     Total emission calculations of terpenoid HC's were first made by Went
(10).  The actual computation of this often-cited work is based on data
supplied by A.J. Haagen-Smit (through a private communication with Dr. Went).
Haagen-Smit analyzed air that was passed over shrubs of Artemisia tridentata
(Basin sagebrush).  After combustion and transformation of the HC to C0~,
                                                    -1  -2
Haagen-Smith calculated that approximately 50 kg day  km   of emissions
                                                           o
resulted.  From this work, Went extrapolated that 1.75 x 10  ton/yr of
volatile natural HC is liberated worldwide.
     The numerous assumptions in Went's calculation include that:  the
average number of emission days is 100 per/year; the vegetation covers 2 x
  5   2
10  km  in the western United States; coniferous and hardwood forest produce
approximately the same amount of volatile organic matter; and, the earth's
                           7   2
total vegetative area is 10  km .  Obviously, Went's number rests upon few
measured parameters.  Also, the basis of all Went's calculations, the
Haagen-Smith work, is not given in detail, which makes validation of the
initial number difficult.  For example, if the air Haagen-Smith used to
fumigate the vegetation contained significant background HC, then the
estimated emissions level from the number is grossly in error, since the
change in C02 would be small upon combustion.  If the change in C02 were not
used in the calculation, then the emission would be too large.
     More systematic research of HC emissions was performed by Rasmussen
and Went (11), who studied several locations in the United States and one
in Holland.  Ambient air samples, as well as plants with plastic containers,
covered were analyzed.  The HC's identified by retention times on the
gas chromatograph (GC) include; isoprene, ot-and 3-pinene, limonene, and
                                    3
myrcene.  Additional hydrocarbons, A -carene, myrcene and p-cymene, were

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tested for retention times, but Rasmussen and Went were not explicit in
stating if those HC's were detected in the ambient air.  The direct measure-
ments of volatile organics in the atmosphere (presumably the summation of
the terpenes and isoprene) showed an average concentration of 10 ppb
(presumably V/V).  This value was then assumed to exist in a 2-km  column
of air, with a yearly production rate of 270 days.  Using an estimated,
                         18  2
vegetated land area of 10  cm , the total world production was calculated  to
            8                                                      7
be 4.38 x 10  ton/yr.  The investigators also calculated 20-40 x 10  ton/yr
by the enclosed plastic container technique, which makes the two above
methods agree within a factor of roughly two, and suggests that the
earlier estimate of Went is too low.
      The work of Arnts et al. (12) that will be described later does not
substantiate the 2-km column height containing 10 ppb terpene.  In fact,
the  terpene concentration was found to decrease exponentially with height.
At 10 m above a tree canopy, the terpene concentration was determined as less
than 30% of that found just at the canopy height.  Considering these
factors, the calculations made by Rasmussen and Went would be reduced by
                                           Q
a factor of over 2000.  Thus, the 4.38 x 10  ton/yr would be reduced to
2.2  x 10  ton/yr.
      In another study, Ripperton et al. (13,14) found the a- and g-pinene/
                                         5           —1   —1              5
ozone reactions to be very fast (0.8 x 10  liter mole  sec   and 0.25 x 10
liter mole" sec  ).  The authors reasoned that ozone may have destroyed a
portion of the emitted terpenes and concluded, because of the ozone/terpene
reaction, that the original estimates of Rasmussen and Went should be
multiplied by a factor of 2 to 10.
      Although these calculations by Ripperton et al. are qualitatively correct,
the two-to-ten fold increase in terpene concentration is difficult to accept.
Since the terpene concentrations were measured within the forest canopy, any
effect from ozone should not be large, and the levels of terpene observed
should be close to the true concentrations emitted without reaction.  If
for example, the ozone concentration is approximately 30 ppb in the
forested area (15), then the half-life is approximately one day for isoprene
and a few hours less for ot-pinene.  (This calculation assumes a constant

                                     6

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reservoir of ozone from a pseudo first-order reaction, though ozone is
actually depleted near the ground by both terpene reaction and dry deposition.)
The OH concentration is also assumed to be zero due to minimal sunlight
penetration into the canopy.  The correction for ozone effects made by
Ripperton et. al. is in fact probably no more than a few percent, if 30 ppb
of 0» and 10 ppb of terpene are involved, which falls well within the
errors contained in the original calculations of Rasmussen and Went.
     Rasmussen  (16)  in a later study measured several terpenes emitted from
various types of deciduous and coniferous vegetation.  These HC's were
 a, and  3-pinene, camphene, limonene, myrcene, and 3-phellandrene, isoprene
was also found  to be emitted from hardwoods.  Emission rates were measured
by placing an undamaged portion of  the plant sample in a glass bell jar.
The HC buildup  in the bell jar was  then measured at several levels of
radiation exposure  (50 to 1200 ftc) and at two different temperatures (17
and 30-32 C).   Coniferous types of  vegetation were found to emit terpene
independently of light, while deciduous plants emitted isoprene in a
linear dependence upon light intensity.  Alpha-pinene emissions from
conifers were found to increase by  a factor of 4 to 7.5 when the temperature
was increased from  17 C to 30-32 C.
     Rasmussen  further gives the percentage of hardwood and softwood
forest in the United States.  From  the foliage per acre given by others
 (17-19), global natural HC emissions are given.  Rasmussen estimates from
his emission rates  that a 10-cm foliar canopy would result in a worldwide
natural HC level of 23.4 x 10  metric ton/yr.  A 50-cm thick canopy would
result in 117 x 10  metric ton/yr;  75 cm in 185 x 10  metric ton/yr; and
finally 200  cm  in 464 x 10  metric  ton/yr.  The abstract of the paper
suggests that the 75-cm canopy value of 175 x 10  metric ton/yr is the
most reasonable.  We have been unable to determine from the manuscript his
method of extrapolating from the individual emission rates of the clipped
branches to  worldwide emissions or  the validity of this method.

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     In successive studies, Tyson et al. (19) and Dement et al. (20)
measured emissions from the sagebrush, Salvia mellifera.  This shrub is
distributed throughout the coastal region of California and covers approx-
imately 45% of the site studied.  The investigators found that the emission
levels of terpene were over an order of magnitude lower than the findings
of Went (10), i.e., 3 kg day"1 km2 versus Went's 50 kg day"  km" .  In the
Dement et al. study, the same sagebrush was investigated under light and
dark conditions, as well as different relative humidities and temperatures.
These investigators found that the emission rates were dependent upon leaf
temperature, but were independent of light.  They also found that relative
humidity was a factor in the emissions.  Thus, emissions almost doubled
(3.1 yg/dm  versus 5.8 yg/dm ) when the air dew point was 22°C compared to 0°C.
Also determined was that the level of HC an excised branch will liberate is
                                                   2                 2
more than twice that of an uncut branch (13.1 yg/dm  versus 5.8 yg/dm , at
D.P. = 22°C).  This latter finding is interesting in that it suggests the
Rasmussen value obtained on cut branches overestimates HC emissions.
     The Research Triangle Institute (RTI) in 1974 (21) measured natural
emissions of gaseous organic compounds in the Ohio area.  In this report
worldwide emissions were also calculated.  The authors suggest that the
often cited work of Went (10) and Rasmussen and Went (11) have serious short-
comgings in that only terpenes and their derivatives are considered; the RTI
report lists a much larger number of organic compounds liberated by veg-
etation.  The natural emissions estimate of RTI is based on the carbon
fixation process, assuming that 10% of the available carbon goes to hydro-
carbon emissions.  By this estimate, Rasmussen's emission estimates are too
low by a factor from <-wo to ten.  The total emissions calculated by RTI
                10                                  9
are 0.4-1.2 x 10   ton/yr, with an average of 8 x 10  ton/yr.
     We have difficulty evaluating RTI's estimate, since it considers all
organic compounds including the oxygenates.  Also, the original estimate by
                 g
Went of 1.75 x 10  ton/yr was, as stated earlier, based on the Haagen-
Smit work, in which air was passed over sagebrush and all the organic com-
pounds were analyzed.  Therefore any other organics liberated by the sage-
brush would also have been oxidized to yield C0?.  Again, the work of
Rasmussen and Went is probably in error since a uniform HC column is assumed.

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Furthermore, the 10% emission of the C02  fixation  suggested by RTI  is not
verified.  As stated in the RTI report, "ten percent was an estimate which
appeared to be reasonable."  The ten percent may be reasonable, but two
points are highly unlikely:  (1) that all the material expired by the plants
is necessarily volatile, and (2) that all the EC's would necessarily par-
ticipate in photochemical smog production, i.e. saturated low-molecular-
weight HC's.
     The most extensive work on the measurement of emission rates has been
performed by Zimmerman (22, 23).  His measurement  technique involves an in-
situ enclosure of a portion of the tree or foliage sample with a Teflon
bag.  The bag is partially emptied and then flushed with metered volumes
of air.  The organic compounds are collected in canisters and returned to
the laboratory for detailed analyses.
     In these studies, Zimmerman not only measured emissions from various
types of vegetation, but also examined the different plant species in
different parts of the United States.  The emission rates of some of the
plant species, as given by Zimmerman, are shown in Table 1.  Table 2 shows
the major emissions from selected vegetation.  In  Figure 1, the structures
of selected natural HC's are illustrated.  Zimmerman further divides the
emission rates into different biotic regions according to Dasmann (24).  He
sub divides these regions into latitudinal sectors for average sunlight and
temperature.  Drawn from these assumptions, Table  3 summarizes regional and
total global emissions.  The total worldwide emissions level of isoprene
                             1 /               Q
plus the terpenes is 8.3 x 10   pgC/yr (9 x 10  metric ton/yr.).  This
                                                Q
number agrees reasonably well with the 4.38 x 10   ton/yr value obtained by
Rasmussen and Went (11).
     The agreement of the emissions level for several species measured by
different experimenters appears reasonable.  For example, Tingey (25) measured
emissions in an environmental chamber that enabled control of the light
intensity and temperature.  With live oak, Tingey  found that the emissions are
approximately 30 yg g~ nr~  .  For slash-pine, Tingey obtained an average
emission of approximately 5 yg g~  hr~ .   Zimmerman gives an almost identical
value of approximately 6 yg g~  hr~ .  For loblolly piner Arnts et  al.  (12)

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                 // \v_         Y iv ^           x >  >         />-\  ff



ISOPRENE        p-CYMENE        « - PINENE        0-PINENE        d - LIMONENE
MYRCENE        CAMPHEIME       TERPINOLENE       A -CARENE        OCIMENE
                                      -CH
    a - PHELLANDRENE  |8 - PHELLANDRENE     a -TERPINENE     "Y - TERPINENE
                Figure 1. Structure of some selected natural hydrocarbons.

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found an emission of 3 yg g   hr   at approximately 30°C in a North Carolina
forest.  The Arnts group measured a vertical profile of ot-pinene over the
forest, and by employing an energy balance equation (i.e., by measuring
temperature, water vapor, carbon dioxide, and net solar radiation), they
were able to calculate a-pinene flux values.  The vertical gradient measure-
ments for the a-pinene were difficult and could be subject to several errors.
Assumptions of smooth terrain and constant wind fetch dimensions were also
required.
     Zimmerman, using the bag enclosure technique in North Carolina,
obtained a value of 4.8 yg g   hr   for loblolly pine, which agrees favorably
with the Arnts value.  However, a reassessment of the Arnts  study suggests
that the proper wind fetch may not have been used.  This error arose from
a study of the H_0 and terpene vertical profiles.
    TABLE 1.  EMISSION RATES FOR SELECTED SAMPLES AT VARIOUS LOCATIONS	
Sample Type    *                                  Emission Rate
                                                  (yg g  hr~ )
Raleigh, NC (June 1977)
Oaks
Shortleaf Pine
Loblolly Pine
Red Cedar
Virginia Pine
Pullman, Washington (August - November 1976)
Ponderosa Pine
Hugo Pine
Douglas Fir
Juniper
Spruce
Pine litter
Tampa, Florida (April - May 1977)

Pasture
Laurel Oak
Turkey Oak
Water Oak
Blue Jack Oak
All Oak species (night)

26.1
16.3
4.85
1.14
13.6

2.96
1.78
0.86
3.25
7.26^
132.0

*
288.6
11.2
26.2
27.2
16.5
1.20
«                                                       2
"The pine litter and pasture  emissions are given in yg/m .hr.  In ojjder to
convert the emissions  shown for  the vegetation from yg/g.hr to yg/m  .hr, the
biomass factors must be known.   For the Raleigh, NC in June, the loblolly pine
forest conversion factor  is 709  yg/m  hr = 1 yg/g hr.
                                    11

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              TABLE 2.  MAJOR EMISSIONS FROM SELECTED SPECIES
Vegetation Type
Major Emissions
Pullman, Washington
     Ponderosa Pine

     Lombard! Poplar  (daytime)
     Douglas Fir

 Santa  Barbara, California
     Eucalyptus (daytime)
     Manzanita
     Chemise
 Research Triangle Park, NC
     Dogwood
     Yellow Poplar

     American Sycamore (daytime)
     Eastern Red Cedar

 Research Triangle Park, NC
     Loblolly Pine
     Shortleaf Pine
     Virginia Pine
Tampa, Florida
     All oaks  (daytime)
36% A -carene
25% f?-pinene
14% a-pinene
99% Isoprene
24% a-pinene
 7% d-limonene
 5% g-pinene
40% Isoprene
18% Unknown 1
25% Unknown 2

10% A3-Carene
10% d-limonene
 8% Unknown 3
 5% Terpinolene
74% Isoprene
52% A -carene
26% a-pinene
35% a-pinene
26% d-limonene
19% g^pinene
11% A -carene
53% a-pinene
17% d-limonene
12% g^pinene
11% A -carene
26% Unknown 4
22% a-pinene
10% g-pinene
 8% dglimonene
 2% A -carene
90-99% Isoprene
                                    12

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                           TABLE 2.   (Continued)
Vegetation Type                                   Major Emissions

     Long Leaf Pine                               30% a-pinene
                                                  30% 3-pinene
                                                    8% Propane
     Slash Pine                                   27% a-pinene
                                                  19% d-limonene
                                                  16% B^pinene
                                                  12% A -carene
     Sand Pine                                    44% a-pinene
                                                  352 B-pinene
     Australian Pine  (daytime)                    92% Isoprene
     Saw Palmetto  (daytime)                       85% Isoprene
     Sabal Palmetto (daytime)                     90% Isoprene
     Cypress                                      46% a-pinene
                                                  21% A -Carene
     Sweet gum                                    51% B-Phellandrene
                                                  20% Isoprene
                                                  13% a-pinene
 The  sum of the emissions  is not  100%  since many  small GC peaks were
 present and were not  identified.  Major unknown  emissions are given
 with an assigned number.

The a-pinene levels  determined  by Arnts et al.  (see Figure 2) should
decrease linearly with the H^O.   However, a-pinene decreases with altitude
above the canopy at  a  much higher rate.  If one assumes  that the H-0
measurements are correct,  then  the rapid decrease in  terpene concentration
can be a result of either  a-pinene reactions  with 0,, or insufficient wind
fetch.  Since  the diffusion time  of  a-pinene  for  such small vertical
distances is short,  the terpene could  not react significantly with 0^.
One must conclude that the wind fetch  was improper for suitable measure-
ments, which indicates  the  Arnts flux value for  a-pinene  is too large.
      The apparent agreement between  the Arnts and Zimmerman studies suffers
from  another incompatability as well.  Arnts  found that  70-80% of the

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5
Q
                                                              I—IP   I   I  I  I   I    jl   I  I   I
                                                          C09         •     a-PINENE
I   I   I  I   I   I   I I I

   TEMPERATURE
                                                                      I   I   I  I  I  I  I
   I   I     I   I   I
a>
o
O
O
u-   15 -
LU
oc
o
LL
LU

O
CO
LU
U
     5 -
     31.2
        TEMPERATURE,
                    WATER VAPOR
                    PRESSURE, mb
A CO2, ppm
                  150  250  350

a - PINENE, jug/m3  ' WIND SPEED, cm/sec
                         Figure 2. Loblolly pine forest vertical gradients, 7/18/77, 1035-1100 hrs e.s.t.

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loblolly emissions are due to a-pinene.   Zimmerman suggests  35%.   The
findings by Arnts are more compatible with the work of Mirov (26)  in which
the reported gum turpentine had a  composition of  71% a-pinene and  22% ct-
pinene.  If we assume the emissions  to be proportional to  the composition,
the pine should liberate higher levels of a-pinene.   Perhaps the disagree-
ment in emission percentages rests on the two measurement  techniques;
Rasmussen (2 7) found the emissions from Mango foliage depend on the type
of enclosure.  Unenclosed, very little isoprene was  liberated and  the
isoprene/n-butane ratio was quite  small.   However, when sheltered, the
isoprene/n-butane ratio was greater, with isoprene increasing some forty-
fold.
     RasmusSen (28) recently suggested that the bag  enclosure technique may
not be a satisfactory way to measure emissions at least for  deciduous-type
vegetation.  His unpublished work  has shown that  when a cylinder is placed
over a tree branch and the emisisons are  measured dynamically, the emissions
levels are much lower.  He suggests  that  perhaps  the emissions are over-
estimated by as much as a factor of  10 with the bag-enclosure technique.
If the Rasmussen findings prove correct,  then the Zimmerman  worldwide
                         Q
emission factor of 9 x 10  ton/yr  must be revised downward.   The Rasmussen
position is consistent with the observations of Lonneman et  al. (29), who
calculated that at best only  5% of  the total nonmethane hydrocarbon (TNMHC)
in the Tampa St. Petersburg area could be attributed to natural emissions.
In contrast, Zimmerman (30) calculated that 68% of the TNMHC is due to
natural sources,a percentage based upon accurate  anthropogenic emissions.
     Of course, the above emission estimates could be in error.  If the
Lonneman estimate is correct for the Tampa St. Petersburg  area, then the
worldwide emission of natural HC's (isoprene and  the terpenes) is  not
9 x 10  ton/yr as suggested by Zimmerman, but closer to 10 -10  ton/yr.
This value is smaller by a factor  of 10-100 than  that originally proposed
by Went, but is nonetheless more compatible with  ambient air analyses.
We shall see in a later section that the  emission rates must be lower than
those given by Zimmerman, since air  quality data  do  not substantiate high
emission values.
                                      15

-------
      TABLE 3.  ESTIMATED U.S. AND GLOBAL EMISSIONS BY LATITUDE (gC/yr)
Latitude U.S.                      Isoprene                 Terpenes

45-50°                             1.8 x 1011               4.6 x 1012
40-45°                             5.8 x 1011               1.0 x 1013
35-40°                             4.3 x 1012               1.6 x 1013
25-35°                             1.5 x 1013               1.9 x 1013
Global  (temperate)                 9.6 x 1013               2.3 x 1014
Global  (tropical)                  2.5 x 1014               2.5 x 1014
Total Global                       3.5 x 1014               4.8 x 1014
                                    16

-------
                                 SECTION 5
                   REACTIVITIES OF NATURAL HYDROCARBONS

     The suggestion has been made that natural HC's are not observed in
high concentrations in the atmosphere since they, being mostly olefinic
react very quickly with the OH and 0., usually present in the ambient air
(31, 32).  Qualitatively this premise is correct.  Biogenic HC's, like all
organic compounds (including methane), will participate in OH ractions.  If
the compounds are olefinic, they will also participate in 0- reactions.
Rate constants for some selected natural HC's are shown in Table 4.
     Went (10) suggested that natural HC's react with ozone in the
atmosphere to produce aerosols since a blue smoke appeared when ozone and
crushed pine or fir needles were placed into a jar.  In a later publication,
Went suggested that a large portion of condensation nuclei present in the
atmosphere is a direct result of photochemical reactions similar to those
responsible for the production of photochemical smog.  Stephens and Scott
(39) studied the photooxidation of monoterpenes,  specifically pinene and
a-phellandrene, when investigating the relative reactivities of a number of
HC's.  The found a-phellandrene to be very reactive at a rate slightly
greater than tetramethyl-ethylene.  The pinene was about six times slower
in reactivity, but slightly faster than isobutene.  The pinene isomer
studied is not given.
     Ripperton et al. (14) studied the a-pinene/ozone reaction, in which
they noted the production of aerosols.  Although a second-order rate
constant is given (0.24 ppm~  min~ ), the experimenters found that much
more a-pinene reacted than ozone.  In two replicate runs, the a-pinene/0.,
consumption ratio was approximately 2/1 and over 3/1, respectively.  The
work suggested that a reactive product is produced (free radicals) that
will react further with the a-pinene.
                                    17

-------
                TABLE 4.   RATE CONSTANTS FOR SELECTED HC's

Compound Reactant Rate Constant (ppm~ min ) Reference
n-Butane

Propylene

Isoprene

Trans-2-Butene

ot-Pinene

3-Pinene

d-Limonene

Myrcene

3-Carene

p-Cymene

a-Phellandrene

g-Phellandrene

o
OH
°3
j
OH
°3
OH
o
3
OH
°3
J
OH
°3
•J
OH
°3
•J
OH
°3
OH
°3
^i
OH
°3
OH
°3
OH
°3
OH
slow
3.5 x 103
1.6 x 10~2
3.8 x 104
1.9 x 10~2
1.2 x 105
0.39
1.0 x 105
2.1 x 10"1
1.2 x 105
5.8 x 10"2
9.8 x 104
0.96
2.1 x 105
0.18
3.4 x 105
0.18
1.3 x 105
6 x 10'7 *
2.3 x 104
1.7
—
2.6 x 10"1
1.7 x 105
—
NBS (33)
NBS (33)
NBS (33)
Arnts (34)
Winer (35)
NBS (33)
Atkinson (36)
Grimsrud (37)
Winer (35)
Grimsrud (37)
Winer (35)
Grimsrud (37)
Winer (35)
Grimsrud (37)
Winer (35)
Grimsrud (37)
Winer (35)
Pate (38)
Winer (37)
Grimsrud (35)
__
Grimsrud (35)
Winer (37)
*

  This rate constant is for p-xylene but p-cymene should have a rate

  constant very similar to xylene.




     Lillian (40) also studied a-pinene reactions, but in the presense of


NO .  He found that irradiated a-pinene/NO  mixtures produced the same
  X                                       X

characteristics as photochemical smog, i.e., the reaction of HC's, the




                                     18

-------
oxidation of NO to NO-, and  the  production of ozone.   Alpha-pinene was also
found to act as both a source  and a sink for ozone, and to be a source of
light-scattering aerosols.
     The most complete study on  the reactivities of monoterpenes is the
work of Grimsrud et al.  (37).  These investigators studied the reactions
of natural HC's with ozone and with NO .  The compounds investigated were-
                                       X
p-menthane, p-cymene, a-  and $-pinene, isoprene, 3-carene,a - and 3-
phellandrene,y -terpinene, carvomenthene, limonene, myrcene,  cis-ocimene,
terpinolene, and qt-terpinene.  Isobutene was also studied  as a reference
organic compound.
     In general, compounds with  high ozonolysis rates also have very high
photooxidation rates.  Grimsrud  et al. found that all the  HC's except
ocimene and terpinolene  showed 1:1 stoichiometry with ozone.   Ocimene  is a
triolefin and ozone is expected  to react with more than one double bond.
Terpinolene showed 1:2 stoichiometry due to the presence of two double
bonds, but only at high  0_/HC  ratios.
     The photooxidation  of four  C-_ terpenes in the presence of NO  was
investigated by Westberg (41).   The  four terpenes were:  limonene, a-pinene,
terpinolene, and ocimene.  In  each compound the amount of  ozone produced
was found to be dependent upon the HC/NO  ratio.  Westberg's data are
                                         A
shown in Figure 3 for  the two  levels of NO .  The curves show that the
                                           x
optimum ozone varies somewhat  for different terpenes.  The maximum ozone
is produced between the  13/1 ratio for terpinolene (NO  =  .05 ppm) and the
                                                       ji
28/1 ratio for limonene  (NO  = 0.20 ppm).  Higher ozone levels were observed
                           
-------
         300
                                                                                 T
ro
o
          200
       .0
       Q.
       Q.
       X
       <
       o
       N
       O
          100
                                                                          LIMONENE I •

                                                                          LIMONENE II-
                                NOX = 0.05 ppm

                                NOV = 0.20 ppm
                                                             	TERPINOLENE I-  NOX = 0.05 ppm

                                                             	TERPINOLENE II-  NOX = 0.20 ppm

                                                             	a-PINENE-      NOX = 0.20 ppm
                                   10
20
                                                        HC/NO,
30
40
                                     Figure 3. Ozone prediction as a function of HC/NOX.

-------
ro
                                                                                                       /  /
                                                                                         CHAMBER CONDITIONS:
                                                                                            2S°C
                                                   48     SO      60      n      80
                                                    C/NOX RATIO, PpmC VS ppm NOX: (N0x)o = 0,33 ppm
                                                                                                      7  t
                                    Figure 4. Effect of hydrocarbon to NOX ratio on ozone maximum.

-------
     Arnts and Gay (34) investigated the reactivities of six C-jgH-g mono-
terpenes, a C-_H.._ aromatic, and a C,-Hg diolefin.  The terpenes were
myrcene (acyclic triolefin), d-limonene and terpinolene (monocyclic
diolefins), a- and g-pinene, and A -carene (bicyclic monolefins).  The
aromatic studied was p-cymene (p-isopropyl toluene), while the C,. diolefin
was isoprene (2-methyl-l,3-butadiene).  Propylene was also studied because
this olefin serves as a reference for the other compounds, and is often
used to test chamber reactivity compound.  The monoterpenes were found to
oxidize NO to NO. at a rate equal or faster ttanpropylene.  The aromatic
p-cymene was very slow in the NO conversion.  The monoterpenes did not
permit the buildup of ozone, which was very noticeable at the higher HC/NO
                                                                          X
ratio  (Figure 4).  Propylene and isoprene were found to be more efficient
in producing ozone than the C-n terpenes.  These compounds also showed
some ozone suppression at the higher HC/NO  ratios.  Para-cymene showed
                                          X
almost no HC/NO  dependence above a HC/NO  ratio of 3 and almost no reaction
               X                        X.
with 0».  Ozone  suppression is probably caused by the very rapid reaction
of 0. with the monoterpenes.
     With the exception of p-cymene, the maximum 0. shown in Figure 4 is
observed to occur between 10 to 20.  This result agrees well with Westberg
(41).  The probable causes for the peaking of 0- are:  (1) at the initial
low HC/NO , the  NO acts as an 0_ scavenger and quickly titrates any 0,
         X                     J                                     j
produced with excess NO, and (2) at high HC/NO , the excess HC reacts very
                                              X
quickly with 0_, leaving insufficient NO  to generate more 0_.
              O                         X                   j
     Lifetimes of some HC's at ambient air concentrations of OH and 0« are
given in Table 5.  As shown in this table, many natural HC's are expected
to oxidize quickly, along with many of the manmade HC's.  At night, the
OH radical concentration is expected to drop to zero since these radicals
are light dependent.  Also during nighttime hours, ground base temperature
inversions decouple the surface ozone from layers aloft.  Ozone concentration
consequently decreases even to zero near the surface from deposition losses
and chemical reactions.  The natural HC's emitted during nighttime are thus
expected to persist until the following day.  However, isoprene is not emitted
at night and monoterpene emissions are minimal at night, since the temperature
                                    22

-------
                       21

                       18

                       15

                       12

                       9

                       6

                       3

                       0
                               1,2.4-TRIMETHYL BENZENE
                                     d-LIMONENE
                                                         mjj-ETHYL TOLUENE
                                                             I         I
                                                                 "• —I
ro
30

25

20

15

10

 5
                                          CYCLO PENTANE (ISOPRENE)
                                                                                    	9T  2-METHYL PENTANE
                                                                                            I        I        I
                       0000    0200
                  0400     0600
0800
1600
1800     2000
                              1000     1200    1400
                                  TIME, hour of day
Figure 5. Diurnal variation of hydrocarbon compounds, Chickatawbut Hill, July 18,1975.
2200
2400

-------
ro
                     60
                     s"
                   u


                   f


                   §«
                   CO
                   oc
                     30
                   <20
                     0000
0300
                                                                                                  AUGUST 23,1976
                                                                                                  SEPTEMBER 8,1976






                                                                                                  FEBRUARY 7,1977


                                                                                                  MARCH 17,1977
0900
 1200

TIME, hr
1500
1800
                                                                                                    2100
2400
                    Figure 6. Total concentration of the C-JQ terpene hydrocarbons (ppb C) observed in the canopy
                    at the IBP site at different times of the year.

-------
f\>
en
                       20



                       18
                     00
                     cc
                       16
                        14
                     a
                     ^  4
                     a
                         0000
0300
0600
0900
 1200
TIME, hr
                                                                                 1SOO
                                                                                                  SEPTEMBER 8,1976

                                                                                                      	•	.
                                                                                                      FEBRUARY?, 1977

                                                                                                  MARCH 17,1977
                                                        1800
2100
2400
                       Figure 7. Total concentration of the CIQ terpene hydrocarbons (ppb C) observed above the
                       canopy at the IBP site at different times of the year.

-------
is lower.  Table 5 shows that some natural HC's can be expected to survive
the attack of OH and 0., long enough to be observed in the ambient air,
especially p-cymene.  However, the amount of natural HC's observed in
ambient air analyses is very low.
     Data obtained in a number of cities, including Tampa/St. Petersburg,
Miami, Tulsa, Houston, and Boston, show practically no C-_ natural HC's
and very little isoprene (see Table 6).  Similar low concentrations of natural
HC's were obtained by Arnts and Meeks (43) in the Smoky Mountains of
Tennessee and in Rio Blanco, Colorado.  Arnts and Meeks found a maximum of
5.7 ppbC isoprene in the Smokies when TNMHC was 102 ppbC; isoprene was found
at 5.6 ppbC in Rio Blanco when TNMHC was 117 ppbC.  No a-pinene or other
terpenes could be detected in the Rio Blanco samples.  In the Smoky Mountain
samples, p-xylene and a-pinene were not separated.  However, their combined
concentration  was only a maximum of 2.5 ppbC when the TNMHC was 171 ppbC.
     Some diurnal variations of natural HC's are shown in Figure 5,6 and 7.
Figure 5 illustrates the data obtained at Chickatawbut Hill southwest of
Boston.  Red oak trees, which are known isoprene emitters, grow in the
area surrounding this site.  The isoprene in Figure 5 is shown with cyclo-
pentane  since GC separation did not distinguish between these two HC's.
However, since roadway samples show 3/1 ratio between cyclopentane and 2-
methyl-pentane, the assumption is reasonable that the increases in cyclo-
pentane/ isoprene concentration are mostly du.i to increases in isoprene—
especially since the increases occur during daylight hours when deciduous-
type vegetation is active.
     Figures 6 and 7 show the diurnal variations of the C-n terpenes found
at a loblolly pine forest in North Carolina.  The Figure 6 data were taken
within the loblolly forest, while the Figure 7 data were obtained 5 m above
the canopy.  These figures contrast with the hardwood forest at Chickatawbut
Hill in that the terpene concentration is highest at night.  Noctural
inversions serve to contain natural HC's within the canopy, and pine
emissions are not directly affected by the presence or absence of sunlight.
Also shown in these figures is the large difference in concentration
between summertime and wintertime.  Of note is that just 5 m above the
                                    26

-------
canopy the natural HC's dropped  to  one third of  the  concentration within
the canopy.  On August 23  of  the study, the biogenic contribution to the
TNMHC was 40% in the  canopy.   At 5  m above the canopy,  the  biogenic con-
tribution is just 12%.
  TABLE 5.  HALF-LIFE IN HOURS FOR SELECTED HC's AT VARIOUS OZONE CONCENTRATIONS2
Ozone Concentration (ppb)
Compound
n-Butane
Propylene
t-Butene-2
Isoprene
a-Pinene
d-Limonene
Myrcene
3-Pinene
3-Carene
p-Cymene
g-Phellandrene
Toluene
m-xylene
0
165
15.2
5.61
4.81
4.81
2.75
1.72
5.88
4.44
25.1
3.39
63.5
16.5
30
Same
9.31
0.86
4.16
1.32
0.35
0.19
3.26
1.4
Same
1.03
Same
Same
50
Same
7.40
0.55
3.40
0.89
0.22
0.12
2.37
0.99
Same
0.70
Same
Same
80
Same
5.66
0.36
2.96
0.60
0.14
.09
1.75
0.68
Same
0.47
Same
Same
100
Same
4.80
0.29
2.68
0.49
0.12
0.07
1.48
0.56
Same
0.39
Same
Same
150
Same
3.65
0.19
2.22
0.39
.09
0.05
1.08
0.39
Same
0.27
Same
Same
200
Same
2.92
0.14
1.86
0.26
0.07
0.03
0.85
0.29
Same
0.21
Same
Same

a                           —8
  OH concentration = 2 x 10   ppm
     A summary of  the ambient air measurements  is  given in Table 7, showing
that the highest values are recorded by Rasmussen  and Went (11) and by
Whitby and Coffey  (46).   High-resolution GC columns were not available at
the time of  the Rasmussen and Went (11)  study,  and many unidentified GC
peaks were assumed to be natural HC's in the Whitby and Coffey report.  They
made this assumption largely because the samples were collected in farmland
areas.  Indeed, if both of these studies are excluded from the table,
the average  isoprene concentration measured in  ambient air lies between
0.1 and 10 ppbC, while the predominate monoterpene, a-pinene, lies between
                                     27

-------
TABLE 6.  HC's FOUND NEAR SEVERAL CITIES (PPB V/V)

Compound
Ethane
Ethylene
Propane
Acetylene
Isobutane
n-Butane
Propylene
Isopentane
n-Pentane
Isobutylene
T-Butene-2
C-BuT-2-Butadiene
Pentene-1
2-Mebutene-l
T-Pentene-2
C-Pentene-2
2-Mebutene-2
Cyclopentane + Isoprene
2-Mepentane
3-Mepentane
4-Mepentene-2
n-Hexane
Hexene-1
T-Hexene-3
2,4 Dimepentane
Mecyclopentane
CIS-Hexene-2
Unknown
3,3 Dimepentane
Cyclohexane
2 Mehexane
2,3 Dimepentane
3 Mehexane
1C3 Dimecypentane
2,2,4 Trimepentane
1T3 Dimecypentane
n-Heptane
Mecyclohexane
Toluene
Unknown
Unknown
Nonane
Unknown
Sub-
urban
Tampa/St.
Petersburg
(5-14-76)
3.0
3.8
3.1
4.6
2.5
7.5
0.9
9.0
4.0
1.3
0.6
1.3
0.1
0.3
—
—
—
5.1
3.0
1.8
0
1.7
0.1
0.3
1.9
—
—
—
—
—
-
—
1.6
—
1.3
—
1.1
4.3
7.2
15.1
16.4
2.8
—
N. Sub-
urban
Miami
(5-16-76)
5.7
10.5
19.5
11.3
5.5
16.4
—
22.3
10.2
2.6
2.2
—
0.7
—
1.8
2.1
-
2.8
6.5
4.0
0.1
3.1
0.1
0.1
.2 -
—
—
—
—
—
—
—
—
—
1.5
—
1.5
1.2
6.1
0.6
0.4
0.4
—
Tulsa
(7-27-78)
11.6
11.5
15.5
8.4
8.1
16.5
4.2
17.3
12.1
1.2
1.6
—
0.8
0.6
-
-
-
3.6
6.3
4.5
-
6.1
0.41
—
5.1
-
-
—
-
1.8
5.0
3.3
5.7
1.02
4.6
2.02
6.12
6.68
16.8
—
—
1.9
__
Houston
(4-2-74)
41.8
78.2
63.9
7.7
39.7
71.1
27.9
77.4
42.8
21.0
1.8
2.5
1.3
2.1
9-. 6
1.7
1.6
36.5
*
24.9
0.0
27.9
—
—
1.1
12.4
—
—
—
—
20.5
7.8
3.5
10.2
14.7
—
13.3
15.8
90.5
—
—
6.6
~._
S . Sub-
urban
Boston
(7-31-75)
3.6
INT
6.2
4.2
4.1
9.6
1.4
11.6
6.3
1.9
0.9
1.6
0.6
trace
trace
—
—
2.3
6.3
4.2
—
4.7
—
0.2
0.5
2.5
—
—
—
0.7
2.3
1.0
1.8
—
1.0
—
1.5
0.6
24.2
—
—
3.3
«.«.

-------
                            TABLE 6.   (CONTINUED)
                               Sub-                          ——
                              urban      N. Sub-                       S.Sub-
                             Tampa/ St.    urban                         urban
                           Petersburgh   Miami     Tulsa     Houston   Boston
Compound                     (5-14-76)   (5-16-76)  (7-27-78)   (4-2-74)  (7-31-75)
Ethylbenzene
P-Xylene
M-Xylene
Unknown
a-Pinene
0-Xylene
Unknown
Isopropyl benzene
N-Decane
g-Pinene
N-Propylbenzene
M-Ethyltoluene
A-Carene
1,3,5 Trimebenzene
0-Ethyltoluene
1,2,4 Trimebenzene
Unknown
D-Limonene
p-Diethylbenzene
1.4
1.2
3.3
0.5
—
4.1
—
1.4
—
—
0.6
1.4
—
0.8
—
0.9
—
—
— —
1.4
2.6
—
0.5
_,.
—
—
—
—
__
1.0
0.4
__
0.6
1.4
—
—
—
— —
2.59
1.6
5.3
— _
__«
3.3
__
—
2.3
— «
	
3.3
__
1.92
—
2.1
—
—
—
13.0
28.2
36.7

	
14.6
__
28.5
11.2
___
2.7
10.6
__ '•
4.3
1.0
11.6
4.0
__
5.9
2.3
2.3
7.3


4.8
2.0
1.1
_ _
_«.
0.8
3.1
«_
1.0
0.3
6.0
__
__
—

*
  Measured with 3-methyl  pentane
less than 0.1 to 14 ppbC.   It  is not clear why Cronn and Harsch  (51)
                                       3
observed such high concentrations of A -carene in the Smoky Mountains.
From Table 2, it is noted that ponderosa pine, dogwood, eastern  red
cedar, loblolly pine,  shortleaf pine, Virginia pine, slash pine, and
                  o
cypress all emit A -carene.  However, this area contains; Canada hemlock,
eastern hemlock, pitch pine, white ash, yellow buckeye, sugar maple,
basswood, yellow birch, yellow poplar,  American beech, mountain  silverbell,
black cherry, mountain laurel, northern red oak,  rhododendron, and
                                  3
cucumber tree.  We suspect that A -carene has  been misidentified.  This is
especially suspect since  only  one aromatic toluene was identified and high
values of A3-carene were  observed when the acetylene concentration was
also high.  This suggests  that the samples were contaminated with auto exhaust,
assuming acetylene as  properly identified.
                                    29

-------
                                                          TABLE 7.  Summary of Blogenlc Hi: Concentrations In Ambient Air
u>
o
Investigator-Sampling
location(s)
Rasnussen & Went (11)
Ozark Plateau, MO



Gray Summit, HI
Highland Biological St.NC
Gray Summit, HI



Rasnussen, et.al. (44)
Elkton, HI
Surrounding
vegetation
Hardwood forest
& prairie



Junipers *
Hardwood forest
Hardwood forest
meadow


Hardwoods &
farmland
Blogenlc
hydrocarbon
Isoprene
a-pinene
p-olnene
limonene
myrcene
totaled
totaled
totaled



laoprene

Avg , Cone .
ppbC
totaled

106


41
50
109



6

Max
ppbC
150




60
120
340



28

Min
ppbC
70




30
10
10



0

TNMHC I % Comments
ppbC Uogenic automotive
Lowest levels ob-
served lust before
aunrlse: hlih levels
observed when
deciduous foliage
— — — changes color in
- — the autumn; high
- — — level of volatiles
observed after grass
was mowed; packed
column GC-FID
98 6 12 79 measurements;
most Intensive study
Lonneman «t.«l.   (45)
  Chlckatawbut Hill, HA

Whltby & Coffey   (46)
  Adirondack Mountains ,HY
                                          Oak & other
                                          Coniferous
                                          forest
                                          Deciduous/
                                           coniferous
                                           forest
                                                              Isoprene
'terpene
  species'
'lighter
  species'
'terpene
  species'
'lighter
  species'
            Lonneman,  et.al.   (29)
              St.  Petersburgh/Tampa,
              Miami and the Everglades,
              Florida
                              Orange groves, gum  Isoprene
                              Cyprus, oak, wax    d-llmonene
                              myrtle, black       a-pinene
                              Willow, persimmon   g-pinene
10(1 day)


33

63

12

IB
               1:61
               0
               0
               0
34


72

123

17

21


4.5
 5.3

29.3

 6.5

 14


 0.1
                                                                                                                106
                                             4
                                             (•ax)
                                                                                                                                    61
                                                                                                                                                yet performed.cc -
                                                                                                                                                FID high resolution
                                                                                                                                                SCOT column

                                                                                                                                                SCOT column
Chromatographlc peato
not Identified;
authors assumed
biogenlc origin due
mainly to rural
location; packed
column CC-FID.
                                                                                                                                     gc-fld; WCOT columns

-------
TABLE 7.  (Continued)
Investigator-Sampling
Jocation(s)
Schjoldager & Wathue (47)
Gjerdrum, Norway


Seila (48)
Jones State Forest,
(38 mi North of Houston,
Holdren, et.al (49)
Moscow Mountain, North-
Central Idaho





Arnts & Meeks (43)
Tulsa (Suburban) OK
Rio Blanco, CO


Smokey (its. , TN

Air Resources Board (50)
Lake Tahoe High School
CA
Cronn - Harsch (51)
Smoky Hts TN



Surrounding
Jfegetation
Coniferous forest
(spruce & farmland)


Loblolly pine

TX)
Coniferous forest
(pine and fir)






Deciduous
Farmland
Sage Brush,
coarse grass,
juniper, pine
Deciduous
Coniferous
Fine


Deciduous
Coniferous



Biogenlc
hydrocarbon
a-pinene
B-plnene
limonene
isoprene
a-pinene
isoprene

a-pinene
B-pinene
3-carene
limonene
a-pinene
B-pinene
3-carene
limonene
Isoprene

Isoprene


Isoprene
a-pinene
a-plnene
B-pinene

Isoprene
a-pinono
6-pinenc
A -carene
Myrcene
Avg. Cone.
ppbC
14.0
9.5
—
—
3.6
0.1

1.13
0.86
0.64
0.10
1.23
1.73
1.08
0.10
0.45

2.10


3.84
—
9.2
3.9

4
3.9
2.5
7.34
1.76
Other natural hydrocarbons could be identified if concentrations exceed
Alpha-pinene is shown
with p-xylene, maximum
concentration
of both is 2.
Max
ppbC
16.5
19.5
trace
—
7.7
1.2

7.3
4.6
5.4
0.5 .
2.7
5.7
3.7
0.2
1.16

5.63


5.72
—
13.4
8.6

17.4
7.9
3.1
20.8
2.0
0.1 ppbC
44 ppbC.
Min
ppbC
10.5
3.0
—
<0.5
<0.1
<0.1

o.i -
<0.1
<0. 1
<0. 1
0.3 .
<0.1
<0« 1
<0. 1

-------
     The automotive contribution shown in Table 7 was obtained by employing
the Lonneman method (52).  This method uses the TNMHC/acetylene ratio for
tunnels.  With this ratio and knowledge of the acetylene concentration of
the ambient air sample, an automotive contribution can be calculated.  The
Cronn and Harsch samples contained very high acetylene concentrations
making the calculated automotive contribution greater than the total
observed non-methane hydrocarbon concentration in most samples.  Either the
acetylene or the TNMHC concentration is in error.  There is also the
possibility that some of the acetylene could arise from the burning of
wood at camp sites nearby (53).  This would invalidate the Lonneman method
for calculating automotive contribution to TNMHC.
     As stated earlier, isoprene, a-pinene and most certainly p-cymene have
lifetimes that are long enough for observation if their emissions are high,
even though their reactivity is also high.  But p-cymene was not observed
at all, though isoprene and a-pinene were observed at very low levels.
Also, the natural HC contribution to the TNMHC in the Smokies was found to
be very low — usually less than 5% (43) .  The maximum values for isoprene
and a-pinene obtained for the 7-day study (September 21-27, 1978,) were
5.72 ppbC and 1.17 ppbC, respectively, but were not recorded on the same day.
If the Cronn and Harsch work is considered the natural hydrocarbon contri-
bution is still only ,. 20% of the total hydrocarbon burden.  Also the TNMHC
is only ~ 90 ppbC.  This is still a low percentage considering the fact
that the area is surrounded with vegetation.
                                     32

-------
                                  SECTION 6
                             PRODUCT  FORMATION

     As discussed earlier, a number of  studies have shown  that natural HC's
can produce aerosols when undergoing  ozonolysis or photooxidation in the
presence of N0x.  Went, who first observed  a blue haze  by  placing 0  and
pine needles in a bell jar (10),  further suggested that the mechanisms for
removal of natural HC's are similar to  those responsible for smog formation.
In his dissertation work, Rasmussen studied some terpene reactions with 0_
and NO- (54).  Though he was unable to  analyze the aerosol material resulting
from reaction, he did point out  that  the products consisted of compound s
both lighter and heavier than  the parent compound.
     Isoprene was included as  one of  the HC's studied by Schuck and Doyle
(2).  When 3 ppm isoprene were irradiated with 1 ppm NO ,  the products ob-
                                                        X
served were 1.7 ppm formaldehyde, 0.90  ppm  CO, 0.20 ppm peroxyacetylnitrate
(PAN), 2.7 ppm acetaldehyde and  1.2 ppm acrolein.   These investigators were
able to account for approximately 87% of the reacted carbon as identifiable
products.
     When 5 ppm of both pinene and phellandrene were irradiated with 5 ppm
N0_, Stephens and Scott  (39) found that 0.25 and 0.23 ppm  PAN was produced.
Pinene also produced 1.3 ppm aldehyde,  while phellandrene  produced 2.0 ppm.
If formaldehyde is taken as the  aldehyde product,  then  only 4.6 and 6.1%
of the carbon is accounted for,  assuming all the initial HC reacts.
     Haze formation was studied  in New  York City and the Blue Ridge
Mountains by Wilson et al. (55).   They  also synthesized aerosol production
in an environmental smog chamber, and collected the aerosols produced from
the photooxidation of a-pinene by extraction and derivation techniques.  Gas
chromatograms and mass spectra of the extracted compounds  indicated the
presence of pinonic acid and norpinonic acid.

                                     33

-------
     In a later study on haze formation also involving photooxidation of
a-pinene in a smog chamber, Schwartz (56) was able to identify an additional
product, pinononic aldehydes, in the neutral fraction.  Pinonic and pinononic
acids were observed in the acid fraction of the extraction, but in the base
fraction, too little sample was available for analyses.  The aerosols
collected at the Smoky Mountain site also contained the two acids.  The
experimenters concluded from this study that the blue haze is a photochemical
aerosol fueled  in part by the terpene emissions from trees.  Unfortunately,
since no quantitation of the aerosol composition was attempted, one cannot
quantitate the degree of visibility reduction resulting from terpene
oxidation.  One would expect in light of recent findings that the contri-
bution of natural HC's to visibility reduction is minimal ( 57, 58).
     Weiss et al. (57) measured sulfates in submicron aerosols at several
locations.  In the Ozarks, carbon species, not sulfates, were determined
to dominante the haze-producing aerosols.  Stevens (58) made similar ob-
servations in the Smoky Mountains in a study in 1978.
     Arnts and Gay (34), in their study on the chemistry of natural HC's,
tried to identify products arising from the photooxidation of the HC's with
NO .  They studied isoprene, myrcene, d-limonene, terpinolene, a, and 3-
pinene and A -carene.  The major gaseous products observed with the long-path
Fourier transform system-infrared (FTS-IR) are given in Table 8.  The pro-
ducts include, CH20, HCOOH, CO, C02, CH3CHO, PAN, and (CH^CO.  Methyl
vinyl ketone and methacrolein were also observed as derivation products of
isoprene.
     Isoprene showed the highest product accountability (24% of reacted
carbon); the remaining compounds showed gaseous products from 2 to 17% of
the reacted carbon.  Several unidentified absorption bands were also
detected, suggesting additional products.  Using reasonable absorption
coefficients, however, the amount of material attributable to the unidentified
compounds is not very large.  GC analyses performed by Arnts and Gay detected
only a small amount of acetaldehyde, although the GC system was able to
detect hydrocarbons to C.  .  No other products eluted from the GC column.
                                     34

-------
                          TABLE 8.  REACTIVITY AND PRODUCTS BY FOURIER TRANSFORM SPECTROSCOPY
                                    (LONG-PATH INFRARED) AT 60 MIN,a
CO

Compound HC/NO Ratio
•cv
g-Pinene
A-Carene
Isoprene
a-Pinene
Myrcene
d-Limonene
Terpinolene
5.3
6.7
6.2
6.7
6.2
6.7
6.2
%HC Reacted H2
58
60
68
72
73
91
95
0.
0.
2.
0.
0.
0.
1.
CO
94
46
39
33
84
9
2
HCOOH
0.39
0.39
0.44
0.32
0.16
0.35
0.31
CO
0.23
0.50
0.77
0.39
0.26
0.46
0.49
co2
0.4
0.9
0.2
0.6
0.24
0.49
0.69
CH3CHO
0.05
0.33
2.0
1.57
2.35
0.23
0.35
PAN (CH3)2CO
0.018
0.26
0.32
0.2Q
0.70
0.24
0.28
0
0
0
0
0.76
0
0
%ACC
2.1
7.1
24.8
8.9
16.9
4.1
4.9

       Initial HC concentration = 8 ppm compound; products in ppm compound.

-------
     Saunders et al. (59), in analyzing rainwater in the Washington, DC area,
found a compound identified as 3-methyl-furan.  They proposed that the furan
is a by-product from the terpene photooxidation, suggesting an unusual ring
closure mechanism to explain their results.  However, since 3-methyl-furan
has not been observed by other investigators irradiating terpenes, its
production from terpene photooxidation is highly unlikely.  Also, since most
polluted atmospheres contain high ozone levels, the stability of this com-
pound is very doubtful, since it oxidizes when exposed to oxygen.
     The composition of aerosol particles produced from the photooxidation
of terpenes with NO  and reactions with ozone was investigated by Schuetzle
and Rasmussen (60).  For example, the reaction of limonene with NO  in the
                                                                  X
presence of ultraviolet light produced over 30 aerosol products.  These
include aldehydes, alcohols, acids, peroxides, nitro esters of alcohols,
acids and peroxides.  The mass spectroscopic analyses also suggested that
dimetric and possible trimeric reaction products were produced upon photo-
oxidation.  The formation of aerosols from the reaction of limonene with ozone
was found to be much faster than from the photooxidation reaction.  Similar
products were observed with ozonolysis reactions, except for the nitrogen-
containing species.  The aerosols were collected on stainless steel impactor
plates that collect particles greater than 0.5 ym.  The collection of a
smaller fraction size would have been more useful, since a considerable
portion of the aerosols should be below 0.5 ym.  The nephelometer used in
the study suggested that the aerosols account for greater than 50% of the
reacted carbon, a conclusion that qualitatively agrees with the earlier
findings of Arnts and Gay.  However, the nephelometer could also be missing
a large amount of material because aerosols greater than 0.1 ym are not
easily detected (i.e., the amount detected is not proportional to the mass).
     Cronn et al. (61) surveyed particulate samples collected in southern
California.  Compounds that were tentatively identified by high resolution
MS include pinonic acid  (C10H16°3+)» norpinonic acid (CgH^O^), a C^E^O^
isomer and a CgH-.O,, isomer.  The total contribution of the peaks was only
1 yg/m  in the midafternoon sample (1200-1420 PST).  The total mass loading
                                                                3
during this time period for particles of d <_ 3.5 ym was 204 yg/m  .  The

                                    36

-------
sum of these tentatively-identified natural organic aerosols  was  lowest  at
nighttime and the evening hours.    The above data suggest that  the  natural
HC contribution to aerosol  formation in the Los Angeles  area  is negligible.
     A recent study by Hull (62)  has shown pinonaldehyde,  nopinone, and
myrtenol as products produced from the ozonolysis of a-pinene.  This study did
not specify whether the  products  were in the gas or solid phase,  since all the
material collected was introduced into GC-MS.
     Zimmerman et al.  (63)  have suggested that the oxidation  of terpenoids
is an important source of CO in the atmosphere.  These investigators cal-
                                   14
culated that between 4.2-13.3 x 10   g/yr of CO can be generated  from the
atmospheric photooxidation  of isoprene and the terpenes.   Their calculation
assumes that 60-80% of the  carbon in natural HC's can lead to CO  formation.
     The hypothesis of Zimmerman et al. has been tested  recently  in an EPA
study with a-pinene  (see Figures 8 and 9).  Starting with 11.5  ppmC of a-
pinene, 1.3 ppm CO was found after a 6-hr irradiation period, which corresponds
to 11.5% of the original carbon.   The figures show that  the photooxidation
of a-pinene produces high levels of aerosols,  but does not produce high con-
centrations of CO.  The  aerosols are also apparently lost to  the walls of
the chamber, since the number, volume, and surface area  of particles all
decrease after 100 min of irradiation, even though all of the a-pinene does
not react.
     Aerosols were collected at the end of the irradiation, usually after
6 hr.  The total  concentration of the material found on  the filter was only
1.9% of the original starting compound (with 71 mg of a-pinene  in the chamber
initially, and 1.3 mg of aerosol collected).  Obviously,  a problem exists
with these experiments in terms of carbon balance, since the  material was not
observed in either the gas  or aerosol phase.  We have seen earlier from
the work of Schuetzle and Rasmussen that over 50% of the organic material
was observed in the aerosol phase at least for limonene  and terpinolene.  The
aerosol data shown in Figure 9, when reasonable estimates are made with  the
aerosol density and aerosol composition, agree very well with the amount of
material collected.  These  data suggest that a large fraction of  organic
                                     37

-------
OJ
CO
                        1.2 -
                                                 100
                                                                        200
                                                                                                300
                                                               TIME, minutes


                                  Figure 8. Data on photooxidation of alpha-pinene in the presence of NOX.

-------
CO
vo
                                                                        O TOTAL SURFACE AREA x 103

                                                                        D TOTAL NUMBER x 105/cc
                                                                        A TOTAL VOLUME x 102 n3/cc
                 1.0  _
                                                              200                  300

                                                           TIME, minutes


                                   Figure 9. Aerosol data for the photooxidation of alpha-pinene.
400

-------
carbon exists in the gas phase that is not measured, or that the walls of
the chamber are acting as a significant sink for both aerosols and gaseous
products.  In light of the few gaseous products identified by FTS-IR tech-
niques employed by Arnts and Gay (34) (see Table 8), the latter explanation
appears most plausible.
     The CO produced in this latest EPA study is clearly greater than that
found earlier by Arnts and Gay (11.5% versus 0.6%).  However, the EPA study
was conducted over a period of 6 hr, while the Arnts and Gay work was con-
ducted for 60 min, with a-pinene still remaining in the chamber.  The increased
yield in CO is probably a result of further oxidation of gaseous products,
and the total aldehydes are also low.  The EPA study further strengthens  the
position that gaseous oxygenates are not produced in great quantities as
suggested by Ludlam and Bailey (30).
     A significant fraction of the aerosols produced from terpene photo-
oxidation is not likely to lead to CO formation in the atmosphere — certainly
not 60-80% of the reacted carbon!  Duce (64) calculated a fine-particle aerosol
(d < 1pm) lifetime of 4-7 days.  In this time frame, more terpenoid aerosols
could be converted to CO.  However, this process requires several days, not
the 2-5 hr suggested by Zimmerman et al.  Duce further calculates that only
60-140 metric ton/yr of terpenoid is required to explain that POC in the
atmosphere.  The 900 metric ton/yr of terpenoids. given by Zimmerman and
coworkers (63) is clearly not compatible with either particle organic carbon
(POC) observed nor the CO produced in smog chambers.
     Hanst et al. (65) recently investigated the CO balance in the atmosphere.
Their calculations suggest that the oxidation of methane by OH cannot
possibly give rise to the levels of CO currently present in the atmosphere.
Instead, they hypothesize that the photooxidation of natural HC's accounts
for the CO present in the atmosphere.  To this end, experiments were per-
formed for measuring the photodissociation of Cl. and subsequent reaction
of Cl atoms with natural HC's.  Their data with isoprene show that, with
73% of the carbon as CO- and CO, only 45% could be identified as CO.  With
a-pinene, the amount of CO was even less, with CO and C0_ accounting for
only 30% of the carbon.  Only 12% of this reacted carbon could be established
as CO.
                                    40

-------
     Although Hanst et al.  did show more CO was produced than in either the
EPA study (Figure 8) or  the Arnts and Gay work, the amount of CO was still
low, at least for the case  of  a-pinene.   The experimental data shown by
Hanst et al. do not substantiate their conclusions, i.e., that the terpenoids
are responsible for much of the CO in the atmosphere.   Furthermore,  these
investigators have employed Cl, a fast-reacting free radical.   In the
atmosphere, OH radicals  and 03 are the reactive species.  Possibly,  the
high concentration of Cl atoms could have reacted with the aerosols  pro-
duced and resulted in more  CO  than is produced under normal atmospheric con-
ditions.  Certainly, the data  shown in Figure 8 do not substantiate  the
Hanst hypothesis.
     Interestingly,  the  ozone  curve in the irradiation of a-pinene shown in
Figure 8 first increases rapidly, later decreases, and then slowly increases
throughout  the irradiation. A similar observation was made by Arnts and Gay
(34) with d-limonene at  high HC/NO  ratios (greater than 40/1).   Arnts  and
                                   X
Gay explained this double peak in terms of the very rapid reaction between
ozone and the d-limonene, with subsequent photooxidation of the carbonyl
products and NO   later producing more ozone.   This explanation is plausible for
               «*
modeling efforts, since  arbitrarily raising the 0, + propylene reaction rate
by a factor of 10 can produce  a double ozone peak in smog chambers.   But
atmospheric buildup  of ozone in the late afternoon is unlikely because:
(1) smog chambers are atypical since they are efficient sources of NO , ozone
       ^^                                                              2w
production  can continue  when NO  is below the detection limits of the
                                X
instrument  (66),  and (2) in the atmosphere, the solar intensity begins  to
decrease late in  the afternoon.  Therefore, the system will be less  photo-
chemically  active late in the  afternoon.
     A validated  mechanism  for the photooxidation of terpenoids cannot  be
written at  this time.  The  main difficulty lies in the proper identification
of the products arising  from the photooxidation.  In the case of isoprene,
for example, only Schuck and Doyle (2) and Arnts and Gay (34)  have investigated
product formation.   Schuck  and Doyle could account for a large fraction
(approximately 90%)  of the  original carbon (or even more than 90%, since
acrolein identified  by them was probably methacrolein); however, Arnts  and

                                       41

-------
Gay (34) could account for only approximately 44% of the reacted carbon.
They suggest that the remaining carbon may be in the aerosol phase.
     A simplified mechanism is given in the Appendix for the photooxidation
of the naturally-occurring HC's.  Excluded from the mechanism are the
inorganic reactions, since they are fairly well understood (3).
     Most of the reactions shown in the Appendix start with the breaking of
carbon-carbon double bonds with ozone.  Obviously, the C-Q terpenes can also
react with hydroxyl radicals, and the product distribtuion does not appear
to be significantly different when isoprene is reacted with OH instead of
0_.  This situation will probably be true with the monoterpenes as well.
In the case of p-cymene, only hydroxyl radicals are shown to react, because
as shown in Table 4, the reaction with 0_ is slow.
     Nitric oxide is shown with most of the reactions, even with 0_ present.
Although NO and 0- react very quickly, a small amount of NO is always present
in a photochemical system (due to N0» photolysis).  The nitric oxide is used
primarily to convert the hydroperoxyl and peroxyalkyl radical to hydroxyl
and alkoxyl radicals.
     Organic nitrogen-containing compounds aside from PAN, were not shown.
They are obviously produced, however, since RO and RCO_ radicals can be
expected to react with N0~.  As discussed earlier, Schuetzle and Rasmussen
have also reported nitrogen-containing products in aerosols when terpenes
were photooxidized in the presence of NO .
     We have mentioned that a large fraction of the terpene products is ex-
pected to be in the aerosol phase, since upon reacting with OH or 0-, the
fragmented oxygenated products should have a lower vapor pressure than the
parent compound (the monoterpenes have a boiling point greater than 150°C).
Aerosols are produced by quick condensation of the partially-degraded ter-
penoids on pre-existing particles.
                                     42

-------
                                   SECTION  7
                        SOURCE-RECEPTOR RELATIONSHIPS

     Source-receptor relationships are  extremely  important when considering
oxidant production from natural HC's  in the  atmosphere, and  serious questions
have been raised that the published emission rates  are  too high.  Certainly
the experimentally-available ambient  data  do not  suggest  such rates.  However,
even if the rates are high, an unfortunate tendency exists to assume one-to-one
relationships between pollutants  from various sources of  emissions.  For
example, the experimental measurements  would suggest that nitric oxide emissions
from power plants will not  significantly affect ozone production until the
air mass containing them travels  25-30  km  downwind  f 67,  68;.  The reason is a
very low HC/NO  ratio.  The excess NO actually decreases  the ambient levels
              X
of 0« near power plant plumes, which  is quite a different case from the
nitric oxide emitted by auto exhaust  in the  presence of HC's.
     The question then can  be raised  as to the effect of  vegetation on a
city's air quality.  Figure 4 shows that the maximum ozone is generated at a
HC/NO  ratio of approximately 10-20.  However, the  bulk of the natural HC's
     X
is emitted in rural areas where vegetation is so  plentiful,  and NO  sources
                                                                  X
so few, that the HC/NO  ratio is  expected  to be much higher.  These ratios
                      X
have been measured by EPA and Washington State University scientists (69, 70)
and have been found to be as high as  60-100  (with NO levels near or below
                                                     X
the sensitivity of the measuring  instruments-usually less than 1-2 ppb V/V).
Also, using fingerprint HC's such as  acetylene or the xylenes, the major
portion of the HC burden in rural areas is determined to  be  from anthropogenic
origins.  Therefore, insufficient N0x is available  to drive  the photochemical
reactions necessary for significant ozone  production.  The little that is
produced is quickly titrated with excess natural  HC's, which also results in
consumption of natural HC's.  Evidence  for such reactions is shown in Table 5,
where the daylight lifetimes of some  natural and  manmade  HC's are given.  The

                                      43

-------
table also shows that isoprene and a-pinene will nonetheless be transported
into urban areas from forested tracts, provided the emissions of these
compounds are large.
     In order to assess the importance of emissions from forested areas into
a city, a series of calculations was performed using a dispersion equation
( II) .  This equation was derived from the numerical integration of infinite
line sources with respect to upwind distance increments.  Its general form is:
                                         dist.
                                         0

where

     X = concentration of pollutant
     q = source flux
     u - wind speed

The calculations were made with the following boundary conditions:
     (1)  Meteorological stability Class 4
     (2)  Receptor height 2 m
     (3)  Emission height 10 m
     (4)  Inversion height 100 m
                                  2
     (5)  Source flux (a) 100 yg/m min
     (6)  Wind speed (U) 5 m/sec
                        4   2
     (7)  Source area 10  km
     (8)  Source receptor 1 km downwind.

     The concentration of natural HC's found at a downwind receptor, i.e., a
                                      4   2
city 1 km downwind from a forest of 10  km , was determined to be 184 ppbC.
But this concentration is unrealistically high, since (1) the emission levels
assumed were very high, (2) the area assumed (10  km  of forest) was very
large,  and (3) the natural HC, probably isoprene within a decidous forest,

                                       44

-------
or a-pinene within a coniferous  forest,  is a reactive olefin that will undergo
reactions with OH radicals and ozone.  However,  of note is  that when an air
quality simulation model similar to  the  Empirical Kinetic Modeling Approach
(EKMA) (72) is employed, the  184 ppbC  cannot exceed the present air quality
standard of 0.12 ppm.  In fact,  when one considers that terpenes are not very
efficient ozone producers (in terms  of ozone produced per parts per million
carbon) , the amount produced  from the  184 ppbC is less than that predicted
by the air quality model which is based  on propylene/n-butane mixtures.
     If the above calculation is repeated with a-pinene as  the natural HC, and
                        —8
0.05 ppm ( 73> and 3 x  10   ppm as the  steady-state concentrations of 0, and
OH, respectively, are  assumed then the gas phase a-pinene observed in a city
will be 81.4 ppbC.  The aerosol  loading  would contain 102.6 ppbC (60.4 pg/m3),
assuming all the a-pinene reacts to  produce aerosols.
                                                             3
     Total particulate carbon at a concentration of 60.4 yg/m  is much too
high.  As stated earlier, a recent study (58) in the Smoky  Mountains has
                                                       3
shown that the total carbon concentration was 3.3 yg/m  in  the fine-particulate
fraction.  The total carbon in both  the  large and small fractions was only
      3
4 yg/m  .  Even if one  assumes that all of the carbon in the area was of
natural sources, the model overpredicts  the aerosol burden  by a factor of 15.
In fact, part-if not most-of  the organic aerosols were probably of anthropogenic
origin, since the TNHC in the area averaged 120  ppbC,  with  95% being anthro-
pogenically produced.
     The size of the source area in  the  above calculations  is too large,
because few if any areas have 10  km  of dense forest, and  the largest con-
tribution  (50%) of theo-Pinene is received from  the last 5  km of forests.
Hence, even though a very large  area was assumed, the bulk  of the HC load
arises from sources near the  receptor.
     A box-type photochemical model  was  also employed in order to determine
the amount of ozone produced  from slow emissions, HC's and  N0x.  The conditions
employed for this modeling effort were:
                           4   2
     (1)  Source area  of 10   km
     (2)  Diurnal insolation  (    max = 0.52 min   )
                                      45

-------
                                     2                   2
     (3)  HC emission rate at 60 yg/m  min; NO  at 5 yg/m min
                                              X
     (4)  Propylene as surrogate terpene
     (5)  03 initally of 40 ppb V/V
     (6)  5% dilution per hour containing 40 ppb of 03
     (7)  Mixing height of 1.8 km (the summer condition for NC (76)).
     Propylene was chosen as the surrogate terpene since, as stated earlier,
a mechanism for the photooxidation of natural HC's cannot be written.  In fact,
                                                        -2   -1
the use of propylene and a high emission rate of 60 yg/m  min   is grossly
overestimating the photochemical potential of terpenes because propylene has
been shown to produce more ozone on a parts-per-million-carbon equivalent
than most terpenes (Figure 4).
     The Dodge (72) photochemical model used in the calculation indicates that
after an irradiation period of 10 hr, the total ozone in the box of 100 x 100
x 1.8 km  was 70 ppb.  The concentration of ozone remaining after 10 hr is
actually only 30 ppb above that contained in the dilution air, suggesting
that the olefin/NO  mixture contributed very little to ozone formation.  When
                  X
the above calculations were repeated with no initial ozone present, and a HC/
NO  ratio of 200 (by reducing NO ) the amount of 0~ produced after 10 hr was
  X                             X                 .3
12 ppb.  This later ratio is more comparable to actual rural HC/NO  conditions.
                                                                  x  £
One must therefore conclude that even high emission levels of 60 yg/m  min
will not produce significant ozone concentrations.
     Natural HC's emitted within urban areas could contribute to ozone
formation if their emission rates were high.  The HC/NO  ratio found in many
                                                       X
cities is favorable for 0_ production.  But the amount of vegetation in urban
areas is small and natural HC emissions are expected to be low.  Data obtained
in urban areas at a number of cities show very little isoprene and practically
no Clf) natural HC's.  These data were shown in Table 6, including:  Tampa,
Miami, Tulsa, Houston, and Boston.  As shown earlier, isoprene and a-pinene
have sufficiently long lifetimes to be observed if emissions were significant
either upwind from a city or within the urban center.  As for the more reactive
HC's their emissions must also be low, since they were not observed in any of
the samples (even though the sensitivity of the measurements is 0.2 ppbC).
Also, such compounds would be expected to produce copious quantities of fine-
particulate aerosols, which was not observed (76).  Aldehydes were also found
at low concentrations (77).           ,,

-------
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                                      47

-------
14.  Ripperton L.A., Jeffries, H.E., White, 0. "Formation of Aerosols by
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                                     48

-------
29.  Lonneman, W.A. Seila, R.L.,  Bufalini,  J.J.  "Ambient Air Hydrocarbon
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30.  Zimmerman, p.R. "Procedures  for  Conducting Hydrocarbon Emission Inventories
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31.  Sculley, R.D. Correspondence on  "Ambient Air Hydrocarbon Concentrations
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32.  Ludlum, K.H., Bailey, B.S. Correspondence  on "Ambient Air Hydrocarbon
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33.  National Bureau of Standards, "Reaction  Rate and  Photochemical Data for
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34.  Arnts, R.R., Gay, B.W. Jr. "Photochemistry of Naturally Emitted
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35.  Winer, A.M., Lloyd A.C., Darnall, K.R.,  Pitts,  J.N., Jr.  "Relative
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36.  Atkinson R., Pitts, J.N., Jr. "Rate Constants for the Reaction of
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37.  Grimsrud, E.P., Westberg, H.H.,  Rasmussen,  R.A.,  "Atmospheric Reactivity
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38.  Pate, C.T., Atkinson, R. , Pitts,  J.N., Jr.  "The Gas Phase Reactions of
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39.  Stephens,   E.R., Scott,  W.E. "Relative Reactivity of Various Hydro-
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40.  Lillian D.  "Formation and Destruction of Ozone  in a Simulated Natural
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     113:211, 1972.

41.  Westberg H.H., Robinson, E.  "Natural  Hydrocarbons in Photochemical Air
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42.  Altshuller, A.P., Kopczynski, S.L., Wilson, D., Lonneman, W., Sutterfield,
     F.D. "Photochemical Reactivities of N-Butane and  Other Paraffinic
     Hydrocarbons." J. Air Pollut. Contr.  Assoc., 19:787, 1969.

                                      49

-------
43.  Arnts, R.R., Meeks, S.A. "Biogenic Hydrocarbon Contribution to the
     Ambient Air of Selected Areas", U.S. EPA, RTF, NC, EPA-600/3-80-023,
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44.  Rasmussen, R.A., Chatfield, R.B. Holdren, M.W., Robinson, E., "Hydro-
     carbon Levels in a Midwest Open-Forested Area."  Draft Report submitted
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45.  Lonneman, W.A., Seila, R.L., Meeks, S.A. "Preliminary Results of
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46.  Whitby, R.A., Coffey, P.E. "Measurement of Terpenes and Other Organics
     in an Adirondack Mountain Pine Forest."  Journal of Geophysical
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47.  Schjoldager, J., Wathne, B.M. "Preliminary Study of Hydrocarbons in
     Forests." Norsk Institute for Luftforskning, P. 1-26, 1978.

48.  Seila, R.L. "Non-Urban Hydrocarbon Concentrations in the Ambient Air
     North of Houston, Texas."  EPA-600/3-79-010, U.S. Environmental Pro-
     Tection Agency, RTF, NC., February 1979.

49.  Holdren, M.W., Westberg H.H., Zimmerman, P.R. "Analysis of Monoterpene
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50.  California Air Resources Board. "Lake Tahoe Communities Hydrocarbon
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51.  Cronn D.R., Harsch D.E., "Smoky Mountain Ambient Halocarbon and Hydro-
     carbon Monitoring, September 21-26, 1978, Draft Report, U.S. Environmental
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52.  Lonneman, W.A., Kopczynski, S.L., Darley, P.E. Sutterfield, F.D.
     "Hydrocarbon Composition of Urban Air Pollution," Environ. Sci. Technol.
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53.  Sandberg D.V., Pickford S.G., Darley E.F. "Emissions from Slash Burning
     and the Influence of Flame Retardant Chemicals." J. Air Pollut. Control
     Assoc. 25_ 278 (1975).

54.  Rasmussen, R.A. "Terpenes:  Their Analysis and Fate in the Atmosphere."
     University Microfilms Inc., Ann Arbor, Michigan, 1966.

55.  Wilson, W.E., Schwartz, W.E., Kinzer G.W. "Haze Formation - Its
     Nature and Origin."  EPA, CPA, 70-Neg. 172, Coordinating Research
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56.  Schwartz, W. "Chemical Characterization of Model Aerosols."  EPA Report
     No.  650/3-74-011, U. S. Environmental Protection Agency, RTF,  NC,
     Aug.  1974.

                                     50

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57.  Weiss, R.E., Waggoner, A.P.,  Charlson,  R.J.,  and Ahlquist, N.C.
     "Sulfate Aerosol:  Its geographical  extent  in the Midwestern and
     Southern United States."   Science, 195:979, 1977.

58.  Stevens, R.K. Concentrations  and  Organic  Aerosols in  the Great Smoky
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     Fates, Research Triangle Park, NC, January  1980.

59.  Saunders, R.A., Griffith,  J.R., Saalfeld, F.E.  "Identification of Some
     Organic Smog Components Based on  Rain water Analysis." Bio-med. Mass
     Spec., 1:192, 1974.

60.  Schuetzle, D. , Rasmussen,  R.A., "The Molecular Composition of Secondary
     Aerosol Particles Formed from Terpenes."  J.  Air Poll. Control Assoc.,
     28:236, 1978.

61.  Cronn D.R., Charlson R.J., Knights R.L.,  Crittenden,  A.L. "A Survey
     of the Molecular Nature of Primary and  Secondary Components of
     Particles  in Urban Air by  High-Resolution Mass Spectrometry."  Atmos-
     pheric Environ., 11:929, 1977.

62.  Hull, L.   "Terpene Ozonolysis Products."  Paper presented at the EPA
     Symposium  on Atmospheric Biogenic Hydrocarbons, Emission Rates,
     Concentrations, and Fates, Research  Triangle  Park, NC, January 1980.

63.  Zimmerman, P.R., Chatfield, R.B., Fishman, J.,  Crutzen, P.J., Hanst,
     P.L. "Estimates on the Production of CO and H_  from the Oxidation of
     Hydrocarbon Emissions from Vegetation."  Geophys. Research Letters,
     5:679, 1978.

64.  Duce, R.A. "Speculations on the Budget  of Particulate and Vapor Phase
     Non-Methane Organic Carbon in the Global  Troposphere."  Pure and
     Applied Geophysics, 116:244,  1978.

65.  Hanst, P.L.,  Spence, J.W., Edney, E.G.  "Carbon Monoxide Production in
     Photooxidation of Organic  Molecules  in  the Air." preprint, February
     1977.

66.  Bufalini,  J.J., Walter, T.A., Bufalini, M.M.  "Contamination Effects
     on Ozone Formation in Smog Chambers." Environ.  Sci. Technol, 11:1181, 1977.

67.  Westberg,  H., Sexton K., Holdren  M.  "Contribution of  the General Motors
     Automotive Painting Facility  at Janesville, Wisconsin to Ambient Ozone
     Levels."   Report to GM by  WSU, August 1978.

68.  Wilson, W.E.  "Sulfates in  the Atmosphere:  A  Progress Report on Project
     MISTT."  Atm. Environ. 12_, 537 (1977).

69.  Lonneman,  W.  "In:  Proceedings of Symposium on 1975 Northeast Oxidant
     Transport  Study, EPA-600/3-77-017,   EPA, RTF, NC, Feb. 1977.

                                      51

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70.  Westberg, H.H.,  Allwine, K.J., Robinson, E.  "Ambient Hydrocarbon and
     Ozone Concentrations near a Refinery."  EPA-600/7-77-049, U.S.
     Environmental Protection Agency, RTF, NC, May 1977.

71.  Turner, D.B.  "Dispersion Estimate Suggestion No.  4."  U.S. Environmental
     Protection Agency, RTP,  NC, March 4 (1974).

72.  Dodge, M.C. "Effect of Selected Parameters on Predictions of a Photo-
     chemical Model."  EPA-600/3-77/048, U.S. Environmental Protection
     Agency, RTP,  NC, June 1977.

73.  Singh, H.B.,  Ludwig, F.L., Johnson W.B.  "Tropospheric Ozone:  Concen-
     trations and Variabilities in Clean Remote Atmospheres."  Atmospheric
     Environ. 12:2185, 1978.

74.  Campbell, M.J.,  Sheppard, J.C., Au, B.F. "Measurement of Hydroxyl Con-
     centration in Boundary Layer Air by Monitoring CO Oxidation." J.  Geophys.
     Res.  Letters, 6:175, 1979.

75.  Holzworth G.G.  "Mixing Heights, Wind Speeds, and  Potential for Urban
     Air Pollution Throughout the Contiguous  United States."  EPA
     Publication 101, U.S. Environmental Protection Agency, Research Triangle
     Park, NC (1972).

76.  Grojean, D.,  Van Cauwenberghe, K., Schmid, J.P.,  Keley, P.E., Pitts
     J.N.  Jr., "Identification of C--C1Q Aliphatic Dicarboxylic Acids in
     Airborne Particulate Matter." Environ.  Sci.  Technol.  12:313, 1978.

77.  Joshi, S.B. "Houston Field Study (1978)  - Formaldehyde and Total
     Aldehydes Monitoring Program." Report to EPA, Contract No. 68-02-2566,
     Northrop Services, Inc., Research Triangle Park,  NC,  February 1979.
                                     52

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                               APPENDIX
          REACTIONS  INVOLVING SOME  NATURAL  HYDROCARBONS
 ISOPRENE
           H         03
(1)   CH2 = C-C = CH2   	»- CH2C(CH3)CHO   +   H20 + CO + CH20
         CH3         (NO)  METHACROLEIN               FORMALDEHYDE
(2)   CH2 - C-C - CH2  	»• CH3C(0)CHCH2 + CH20 + H20 + CO
         CH3        (NO)  METHYLVINYLKETONE
(3)   CH3-C-C = CH2   -—•-+- CH3C(0)CHO + H20 + CO
                    (NO)  METHYLGLYOXAL
        OH           03      00'
(4)   CH3-C-C-CN2   	» CH3-C-C^2H02+CO
                    (NO)
                             0
                             It
                          CH3-C-H + C02
                          ACETALDEHYDE
            H        OH
(5)   CH2 - C-C » CH2	>•  CH2C(CH3>CHO + CH20
          CH3       NO   METHACROLEIN
                     02
            H              0
(6)   CH2 - C-C = CH2	*" HC-OH + CH20 + H02 + CO
          CH3             FORMIC ACID
        0            OH      0
(7)   CHs-C-H         	*• CH3-C-0-ON02
                     02   PEROXYACETYLNITRATE (PAN)
                     N02
                                  53

-------
 MYRCENE
(8)
                                   ^
                           03   CH3-C-CH3 + CH2CHC(CH2)CH2CH2COOH
                                ACETONE      4-METHLENE-5-HEXENOICACID

                                            CH2CHC(CH2)CH2CH2CHO
                                              4-METHYLENE-5-HEXENAL
 (9)
                   03
                            (CH3)2CCHCH3CH2C(0)CHCH2  + HCOOH
                              4-METHYL-4-PENTENYLVINYLKETONE
(10)
                           (CH3)2CCHCH2CH2C(CH2)CHO  +  CH20
                           6-METHYL-2-METHYLENE-5-HEPTENAL
 a-PINENE
(11)
                           CH3-C-CH3 + CH20 + CH200 + HOOCCH2CH2COOH
                           ACETONE                   SUCCINICACID
                                              54

-------
(12)
                     CH3
                             03 B

                            (NO)
              CH3

       XT
          x^—CHO
(NO)

 02
                                   COOH
                                                      PINONICACID
                            H02 + CO
       PINONONIC ALDEHYDE
 PINONONIC ALDEHYDE
 (13)
                 Hf/OH
                (NO) (02)
                                          COOH

                                   NORPINONICACID
/3-PINENE

(14)
                                       03
                                      ^^•••MMi

                                      (NO)
                                        OH
                                           FRAGMENTATION
                                             PRODUCTS
                                                      NOPINONE
                                      55

-------
(15)
A-CARENE
                         03
                         NO
                                   1-ETHANAL-2, 2 DIM-
                                   ETHYL-3-ACETONYL-
                                   CYCLOPROPANE
           2, 2-DIIWETHYL-3-ACE-
           TONYLCYCLOPROPYL
           ACETIC ACID
(16)

LIMONENE
                                                      + H02

                                                      + CHOOH

                                      4-ACETYL-1-METHYLCYCLOHEX-1-ENE
(17)
         /   \   /    03
         \   /   ^  "i
          \.	/
(18)
                                 3(2-PROPENYL)-6-KETO-HEPTANAL
                                  -i~yj
                                      HC    /
HC
 6
                                  3-ACETYL-6-KETO-HEPTANAL
                                56

-------
(19)
(3-PHELLANDRENE
                            _03_
                            (NO)
                 CH20 + HC02H
                                       4-ISOPROPYLCYCLOHEXENONE
 (20)
                             03
                            (NO)
              V
HOOCC(CH2)CH2CH2-CHCHO
                                         2-METHYLENE-5-ISOPROPYL-6-OXO-HEXANOICACID
  (21)
  P-CYMENE
                              OH
                                              CH3
                                         2-P-TOLYLPROPANAL
  (22)
                              OH
                              02
                +  CH3COCH3

                   ACETONE
                                              57

-------
(23)
                             OH
                                       3-HYDROXY4-ISOPROPYL TOLUENE
                             OH
                             02
                                                            FRAGMENTATION PRODUCTS

-------
                                   TECHNICAL REPORT DATA
                           (Please read Instructions on the reverse before completing)
 REPi
  EPA-600/2-80-086
                                                           3. RECIPIENT'S ACCESSION-NO.
TITLE AND SUBTITLE

 IMPACT OF NATURAL HYDROCARBONS  ON AIR QUALITY
                                                           5. REPORT DATE
                                                              May 1980
                                                           6. PERFORMING ORGANIZATION CODE
 . AUTHOR(S)

   Joseph J.  Bufalini
                                                         8. PERFORMING ORGANIZATION REPORT NO.
9. P
 ERFORMING ORGANIZATION NAME AND ADDRESS
 Environmental Sciences Research Laboratory
 Office of  Research and Development
 U.S. Environmental Protection Agency
 Research Triangle Park, North Carolina 27711
                                                           10. PROGRAM ELEMENT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
   Environmental Sciences Research Laboratory  -RTP,  NC
   Office of Research  and Development
   US Environmental Protection Agency
   research Triangle Park, North Carolina  27711
                                                          13. TYPE OF REPORT AND PERIOD COVERED
                                                            in-house
                                                          14. SPONSORING AGENCY CODE
                                                            EPA/600/09
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT

        The emissions,  reactivities, and ozone-forming potential of natural hydro-
   carbons are discussed.   A review of the data available on emission levels for
   natural hydrocarbons indicates that much more information is needed in order to
   quantify the absolute emission levels, becasuse emissions data do not agree with
   ambient air measurements.,. These ambient air measurements suggest that the previous-
   published value  of  9 x 10  ton/yr needs to  be lowered to 10 -10  ton/yr.  Emissions
   may be overpredicted by a factor of 15 to 20, as indicated by back calculations
   using a simple diffusion trajectory model.   Isoprene, when compared to the mono-
   terpenes, is much more efficient in producing ozone through phooxidation in
   the presence of  NO  .  This greater ozone production apparently occurs because of the
   large amount of  carbon consumed in the formation of aerosols for the monoterpenes.
   Since rural areas have very low levels of NO , vegetative emissions may in fact
   act as sinks for ozone rather than as sources.  All areas investigated show very
   low levels of natural hydrocarbons, suggesting that even if N0x were available,
   very low levels  of  ozone would be produced.   Air quality is thus not found to be
   significantly affected by vegetative emissions.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
a.
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                                                                       c. COS AT I Field/Group
   Air pollution
   Biological productivity
   Hydrocarbons
   Ozone
                                                                          13B
                                                                          08A
                                                                          07C
                                                                          07B
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