United States
                    Environmental Protection
                    Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711
                    Research and Development
EPA/600/S3-85/016 Apr. 1985
&EPA          Project  Summary

                    Chemical  Transformations  in
                   Acid  Rain:  Volume  I.
                    New  Methodologies  for
                    Sampling  and  Analysis  of
                    Gas-Phase  Peroxide
                    Roger L. Tanner
                     New methodologies  for sampling
                    and  analysis of gas-phase peroxides
                    (H2O2 and organic peroxides) using (a)
                    diffusion denuder tubes and (b) gas-
                    to-liquid transfer with prior removal of
                    ozone have  been investigated.  The
                    purpose was the development of an
                    interference-free  method  for  deter-
                    mining H2O2(g)  in  ambient  air. A
                    denuder approach using  ferrous (1,
                    10-phenanthroline)-coated  tubes was
                    unsuccessful for, although H2O2 was
                    removed, the capacity was low  and
                    ozone was  also removed, possibly
                    through surface decomposition  to
                    H2O2  and  its  radical  precursors.
                    Gaseous  peroxide  in compressed
                    airstreams  could  be collected  in im-
                    pingers  without  artifact  formation
                    from  surface ozone  decomposition if
                    O3 was first removed  by  gas-phase
                    titration with nitric oxide.

                     This  Project Summary  was
                    developed  by  EPA's  Atmospheric
                    Sciences  Research  Laboratory,
                    Research  Triangle Park, NC,  to  an-
                    nounce key findings of the research
                    project that is fully documented in a
                    separate report of the same title (see
                    Project Report ordering information at
                    back).

                    Introduction
                     The purpose of this research task  was
                    to develop fundamentally new methods
                    for sampling and analysis of gas-phase
hydrogen peroxide  (H202)  and  organic
peroxides, if possible, through the use of
diffusion-denuder  tubes.   In  addition,
sampling methods for H202  using gas-to-
liquid transfer and capable of avoiding in
situ production of H202 from ozone (03)
decomposition and other processes were
studied. The goal of the research was an
interference-free  method for  gas-phase
peroxides with 0.1 ppb limit of detection
and 15 min time resolution.
  Much analytical effort has been expend-
ed in the past  few years in  measuring
gaseous and aqueous H202 following  the
recognition  that  H202  could  oxidize
dissolved S(IV) rapidly throughout the pH
range of rain, cloud  and fog waters. Fur-
thermore, the high  solubility of H202 in
water led to significant H202 concentra-
tions in cloudwater. Methods  for deter-
mining  liquid-phase  H202  have been
developed  using  several  approaches:
luminol  chemiluminescence, p-hydroxy-
phenylacetic acid   dimer  fluorescence,
scopoletin  fluorescence quenching  and
peroxyoxalate  chemiluminescence.   At-
tempts to  measure  gas-phase hydrogen
peroxide by collection in impingers or by
other dissolution techniques have been
shown to be generally unreliable due to
the in situ formation  of hydrogen peroxide
from low-solubility  constituents  of  am-
bient air during collection by impingers. It
is suspected that surface-initiated ozone
decomposition  via  H02~  and  02~  in-
termediates is the  likely mechanism of
"artifact" H202 formation.

-------
  Two  possible research  approaches for
artifact-free sampling  of H202(g) were in-
vestigated  in this project: selective, reac-
tive sampling onto a coated denuder tube,
employing  H202 redox chemistry and sup-
pression of  in  situ  H202 formation by
selective removal of ozone.
  This  study describes  a  denuder  ap-
proach using ferrous (1,10-phenanthroline)
coated  tubes that was  successful:  the
capacity for H202 was low and ozone was
also  removed,  possibly  through surface
decomposition  for  H202  and its  radical
precursors.   However,  the  study  also
documents that gaseous peroxide in com-
pressed airstreams can be collected in im-
pingers  without  artifact  formation from
surface  ozone decomposition if 03 is first
removed by gas-phase titration with nitric
oxide.

Experimental
  Experiments  in  this  task were con-
ducted  by  using a  system in which  gas-
phase hydrogen peroxide  was reproduci-
bly generated in the 1-500 ppbv  range by
multiple  dilutions  with compressed air,
with  facilities to  subsequently  humidify
the air and add ozone and nitric oxide to
the  diluted  airstream  (see  Figure  1).
Parallel  airstreams were then formed with
appropriate mixing chambers, and perox-
ide was collected in parallel series of 2 or
3 midget impingers that were followed by
flow  meters, charcoal  traps for ozone and
H202, and a common,  selectable inlet line
to the ozone analyzer. Diffusion denuder
tubes  containing   coatings  of  Fe(ll)-1,
10-phenanthroline   were  tested  in  ex-
periments by  placing  them  in the  flow
streams after division at  points A and B,
just  prior  to  impingers  1-1  and  2-1,
respectively. Aqueous H202 in each of the
six impingers was analyzed after each ex-
periment using  the  POHPAA  fluorescence
method by sample injection into a flow in-
jection system.
  For the most of  the experiments  con-
ducted in this task,  an  alternate, manually
operated  "stopped-flow"  approach  to
aqueous  H202 analysis was used. In this
approach, three volumes of sample were
mixed, with one volume of  peroxidase/
POHPAA/EDTA solution in pH 8.5 TRIS
buffer. The premixed sample  was  allowed
to standard for 2-3 min,  and  then an ali-
quot  was  injected   directly  into   the
fluorimeter flow cell for analysis. The flow
cell was rinsed out thoroughly with  TRIS
buffer  between  injections.  Extensive
washing  of  the sample  lines in  contact
with catalase solution was required before
reuse.
Results  and  Discussion
  Considerable  effort  was expended  to
improve   the  POHPAA  fluorescence
technique  for  aqueous-phase  peroxide.
These efforts were  required because low
levels of  peroxide  would have  to  be
analyzed  for passive  denuder-collection
                                                  Mixing
                                                 Chamber
                                                           NO/

                                                           A/2
 H202 samples or for artifact-free impinger
 collections  (if  such  could  be  achieved).
 Without the improved analytical sensitivity
 attained by these efforts, the stated goals
 of this task (0.1 ppbv, 15 min time resolu-
 tion) would  not have been possible. The
 final limit of  detection achieved  during
 this effort was  0.3 ppb  aqueous (~  0.01
 /Jvl), This sensitivity was just barely ade-
 quate  to  attain  the task  goal  for  the
 artifact-suppression  or   denuder   ap-
 proaches.

 Denuder  Tube Sampling
   Pyrex denuder tubes,  0.6 cm  OD by 30
 cm long,  were coated with  ferrous-! 1,
 10-phenanthroline)-sulfate  solution  in
 methanol.  They were then placed in the
 parallel airstreams downstream  from  the
 mixing chamber and, in the case of line 2,
 after the addition of NO  in  N2  to  the
 airstream.  Various  admixtures  of  com-
 pressed air  and ozone and/or H202 were
 passed through the denuders. Nitric oxide
 (6.2 ppm after dilution) was added to line
 2 and  the apparent  H202 in each  of  im-
 pingers 2-1 through  -3 and  1-1 through -3
 (see Figure  1)  was  determined  using  the
 POHPAA  fluorescence  technique.  Four-
 teen experiments  were conducted to test
 the denuder  sampling  technique:  The
 results obtained suggested  the following:
 (1) Ferroin-coated denuder tubes  of  the
    type tested  have limited capacity for
    H202  removal, but they also  remove
                                                                                                           F/M
                                                                                                            2
                                 2-1
   2-2
Impingers
                                                        2-3
                                                          Vent
                                                         Excess
                                                          Thru
                                                        Charcoal
 8410
  03

Monitor
                                                                                                                   F/M
                                                                                                                    1
                                                                            1-1
                                                                                       1-2
                                                                                    Impingers
                                                        1-3
                               I	1
                                Optional
                               Humidifier
Figure  1.    Modified apparatus for W2O2 generation and impinger collection.

                                     2

-------
    03 at continuously decreasing efficien-
    cy.
(2)  Ferroin-coated  denuders do  not pre-
    vent  artifact  H202 formation  in  im-
    pingers downstream of the denuder.
(3)  It appears that ozone  reacting  on the
    denuder surface may generate  artifact
    H202 on  partially  exhausted denuder
    tubes.
  We  do  not wish  to  assert that  all
iron(ll) complexes would  exhibit the same
behavior when used as denuder coatings
as did ferroin,  but only that the denuder
approach  as defined was  heretofore un-
successful  in removing H202 quantitative-
ly.  In  addition, complications  are intro-
duced because  of  co-removal  of ozone
and the likely co-reaction with the ferroin.

Gas-to-Liquid Sampling
After  O3  Removal
  As noted above, previous observations
have  suggested that artifact H202  formed
in gas-to-liquid sampling using  impingers
or other approaches seems to be  related
to levels of ozone and one or more other
air  constituents. As a result, sampling ap-
proaches  in  which  ozone is selectively
removed from the sampled  air may  be
successful   in  eliminating  the   artifact
formation  of  H202 while  simultaneously
transmitting H202 at high, reproducible ef-
ficiency  to  an  aqueous  solution   for
POHPAA  analysis  of  H202. Unreported
data  suggest that  the amount of  H202
formed in  bubblers is  non-linearly related
to  03 concentration in sampled  air, but
since 03 reaction on the bubbler surfaces
appears to be the initial  and limiting step
in artifact  H202 formation, removal of 03
prior  to  sampling   should  effectively
eliminate the process.
  The evidence that titration with  excess
NO removes artifact H202 formation in im-
pinger  collection  of  H202  is shown  in
Table 1. Hydrogen peroxide (calculated to
be 28 + 2 ppb in stream 1 and 22  ± 4
ppb in stream 2) was admitted without O3
or NO in  Expts.  1  and 2; peroxide  was
found in roughly  equal amounts in  bub-
blers 1-1 and 2-1.  No  peroxide was found
in subsequent  bubblers. Ozone at  327 ±
13 ppb  was admitted to the system in
Expts. 3 through 9, with NO (6.2 ppm)
present  in stream  2 only  for Expts. 4
through 9. In  Expt. 3, addition of ozone
alone to both  streams produced H202 in
all impingers with  most being found in im-
pinger  1  of each  stream.  Addition  of
ozone +  H2O2 mixtures to stream 1 and
03/H202/NO to stream 2 (Expts. 4,  5, and
9) produced  additional  peroxide  in  all
stream  1  bubblers consistent with  the
results of Expt. 3,  but no  peroxide  was
formed in  stream 2 bubblers sampling NO-
containing air.
  The amount of artifact  H202 sampled
from  03-containing  airstreams  was
variable,  and  appears to  be  reduced in
Expts. 5 to 9 in comparison to Expts. 1 to
4. Indeed, no artifact  H202 was formed in
impingers  2-2  and 2-3 during  Expts.  6 to
8. In contrast,  only  in Expt. 6 was  a small
amount of H202 found in the 03/NO/air-
stream.  This could  be due to inadequate
mixing of NO with the ozone/airstream,
but is more likely the result  of desorption
of H202  retained  in the  mixing chamber
from  the  previous  experiment.   Never-
theless,  the  preponderance  of  evidence
suggests that ozone is removed sufficient-
ly fast that no measurable artifact  H202 is
formed.
  Artifact  H202  is formed  in  variable
amounts  when  an  airstream containing
about 300  ppb 03  is sampled. Collected
amounts correspond to about 3-15 ppb of
gaseous  H202  in  the first bubbler and
roughly an order of  magnitude lower in
subsequent   bubblers.   This  differs
somewhat from results reported by others
in which roughly equal amounts of perox-
ide  were formed in subsequent bubblers,
and  indeed, it is  different  from our own
early results, suggesting that the extent of
the process in which artifact H202 is form-
ed is quite  dependent on the presence of
other atmospheric constituents in  addition
to 03. That these constituents may differ
widely  in their aqueous solubility is sug-
gested  by the low production rate  of ar-
tifact H202 in impingers 2 and 3 compared
to impinger 1 for the experiments sum-
marized in Table 1.

Conclusions
  The research approaches investigated in
this  task for artifact-free  sampling  of
H202(g)   included   selective,   reactive
sampling onto  a  coated  denuder  tube,
employing H202 redox chemistry and sup-
pression  of in situ  H202 formation by
selective removal of  ozone.
  A  denuder  approach  was  attempted
employing  Fe(ll)-1,10-phenanthroline-
coated   glass tubes.  Hydrogen  peroxide
was  removed by such tubes but collection
efficiencies less  than calculated  values
were observed even with relatively fresh
tubes. This suggested that surface deple-
tion  of  sorption sites was  reducing  the
capacity  of dry coating on the diffusion
tube. In addition, ozone was removed to
a significant extent by the Fe(ll)-phenan-
throline  denuder tubes, which indicated  a
lack  of specificity for H202 and raised the
spectre  of  surface decomposition of  03,
possibly to gas-phase  H02 and/or  H202.
 Table 1.    Collection of H2O2 from Ozone-Containing and Ozone-Free Air Streams
Experiment
No.
;
2
3
4
5
6
7
8
9
H202 (fJ\
Composition
H202/Air
"
O3/Air
03/H2O2/Air
"
03/A/r
"
"
03/H202/Air
VI) in Sampled
Bubbler 1
0.58
0.55
0.36
0.96
0.63
0.15
0.044
0.047
0.69
Gas Stream 1
Ave,
Bubbler 2 + 3
ND*
••
0.022
0.018
0.016
ND
ND
ND
0.060
H202 (fuM
Composition
H2O2/Air
"
O3/Air
03/H2O2/NO/Air
"
03/NO/Air
"
"
03/H202/NO/Air
') in Sampled Gas
Bubbler 1
0.56
0.39
0.31
0.52
0.45
0.026
ND
ND
0.50
Stream 2
Ave,
Bubbler 2 + 3
ND
ND
0.014
ND
ND
ND
ND
ND
ND
 *ND = none detected {•< Blank)
 Gas Phase Concentrations:
    [Ozone] = 327 ±  13 ppb (Expts. 3-9)
    [H2O2]  = 28.0 ± 2.0 ppb I Stream 1); 22.2 ± 3.6 ppb IStnvn 2)
    [NO)    = 6.2 ppm
 Sampling Conditions:
    Air sampled for 30 min 0.50 L/min in each One.

-------
  Thus,  removal of H202 onto denuders by
  nominally  H202-specific  chemisorption
  does not appear to offer significant ad-
  vantages  over gas-to-liquid  sampling for
  gaseous H202 analysis.
    Suppression of in situ production of
  H202 in  gas-to-liquid sampling (bubblers,
  impingers) by upstream titration  of the
  ozone in the sampled airstream has  been
  successfully demonstrated  for cases in
  which compressed air is  used. Gaseous
  hydrogen peroxide  was collected com-
  pletely  (>99%)  in the  first  bubbler
  whereas  confluent  ozone  produced
  measureable peroxides in the second and
  third bubblers; no peroxide was observed
  in the second and third bubblers for those
  experiments in  which 03 (100-300  ppb)
  was titrated by 6 ppm NO prior to bubbler
  collection.  The  addition of  6  ppm  NO
  does  not  significantly  interfere  with
  POHPAA analysis of  collected aqueous
  H202.
         Roger L Tanner is with Brookhaven National Laboratory, Upton, NY 11973.
         Marc/a C. Dodge is the EPA Project Officer (see below).
         The complete report, entitled "Chemical Transformations in A cid Rain: Volume I.
           New Methodologies for Sampling and Analysis of Gas-Phase Peroxide, "(Order
           No. PB 85-174 425/AS; Cost: $8.50, subject to change) will be available only
           from:
                 National Technical Information Service
                 5285 Port Royal Road
                 Springfield, VA 22161
                 Telephone: 703-487-4650
         The EPA Project Officer can be contacted at'
                 Atmospheric Sciences Research Laboratory
                 U.S. Environmental Protection Agency
                 Research Triangle Park, NC 27711
                                             U S GOVERNMENT PRINTING OFFICE 1985-559-016/27031
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
POSTAGE & FEE'S
: ~  fl  PEŁA- i*
I ~ PERMIT No"(i<
Official Business
Penalty for Private Use $300
                                  OOOC329    PS
                                  U  S  ENVIR  PROTECTION  AGENCY
                                  REGION 5  LIBRARY
                                  230  S  DEARBORN  STREET
                                  CHICAGO                IL   6 060 A

-------