Hydrogen Peroxide and Methylhydroperoxide Measurements in RICO

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Hydrogen Peroxide and Methylhydroperoxide
Measurements in RICO
Brian G. Heikes, Haiwei Shen, and Brian Foley
Daniel W. OSullivan
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RICO Peroxide Component

• Goals of our proposal
• Role of the peroxides
• Aqueous phase oxidation of SO2
• Using peroxide measurements to constrain gas
  phase oxidation of SO2
• Using the peroxides to help constrain cloud age
  and/or entrainment
• Measurement techniques
• Hypotheses we hope to evaluate

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Goals of the RICO Peroxide Component

• to help constrain estimates of SO2 oxidation in
  cloud free air by constraining other
  photochemical oxidants like hydroxyl radical, HO,
  and to understand H2O2 and CH3OOH distributions
  in clear and cloudy air in the marine boundary
  layer and lower free troposphere,
• to evaluate the H2O2 and CH3OOH ratio as a
  diagnostic of precipitation or in-cloud
  chemistry,
• to understand the impact of H2O2 and CH3OOH on
  aqueous SO2 oxidation in wet haze, and cloud, and
  the evolution of aerosol sulfate,

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Photochemical Oxidant Processing
D O3 D CO D CO2 D NOx D sulfur
H2O O3 VOCs NOx hn
D O3 D CO D CO2 D NOx D sulfur
H2O O3 HCs NOx hn
HO HO2
HO HO2
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• Marine Boundary Layer at Christmas Island, from
  Chen et al. (2001).
• Symbols are in situ measurements and the smooth
  lines are the photochemical model output.
• Predicted H2O2 and CH3OOH depend on the predicted
  HO and HO2 levels, allowing the observed peroxide
  levels to constrain the HO and HO2 radical levels.

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• Marine Boundary Layer at Christmas Island, from
  Davis et al. (1999).

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Gas phase oxidation of DMS and SO2.

• Use peroxide measurements to constrain levels of
  hydroxyl radicals, HO and HO2.
• Methylhydroperoxide is produce via hydroxyl
  radical oxidation of methane.
• Hydrogen peroxide is produced by HO2 bi-reaction,
  and its subsequent photolysis generates hydroxyl
  radical.
• Gas phase oxidation of DMS and SO2 by hydroxyl
  radical leads to the formation of non-seasalt
  aerosol sulfate.

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Aqueous phase chemistry
O3(g)
Henrys Law i KhPi
H2O2(g)
H2O2(aq)
O3(aq)
Kh eA/T(K) -B
SO2(aq)
SO2(g)
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Henrys Law for Peroxides
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Aqueous phase reactions
Oxidant
H2O2(g)
O3(g)

• O3
• (k0SO2k1HSO3-k2SO32-)xO3
• ko 2.4 x 104 M-2s-1
• k1 3.7 x 105 M-2s-1
• k2 1.5 x 109 M-2s-1
• H2O2
• kHHSO3-H2O2
• k 9.1 x 107 M-2s-1

O3(aq)
H2O2(aq)
SO2(aq)
Hoffman and Calvert (1985)
SO2(g)
Mass Transport Limitations
SO2-O3 pH gt 4.5 SO2-H2O2 pH lt 3.5
Maass et al. (1999)
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Aqueous phase oxidation of SO2 by H2O2

• H2O2 is the principle oxidant for aqueous SO2 at
  pH lt 5, forming non seasalt sulfate (NSS).
• The original aerosol CCN is altered by the NSS.
• Increasing the number of particles
• Increasing the water content of a particular
  aerosol
• Cloud chamber studies have demonstrated aerosol
  growth by in cloud reactions of SO2 and H2O2 and
  O3, Caffrey et al. (2001).

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Distribution with Altitude
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H2O2 CH3OOH
H2O2 CH3OOH
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GOES IR (left) and Visible (right) Images for
DC-8 Flight 7 (July 12, 2004) Brighter regions
on IR image show colder temperatures, higher
cloud tops heights, and deeper convection.
Arrow shows suggested area where very
recent convective outflow was sampled prior to
spiral over WI.
Figure 2b
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DC-8 Preliminary Data Rhinelander WI Spiral
Point B on Map, July 12, 2004
UT
convective outflow
URI CH2O
MHP
P
HP
BL
0
2
4
0
1
2
0.2
1.0
ppb
ppb
bar
Upper troposphere (UT) shows evidence of
convective outflow (convect) elevated CH2O and
elevated CH3OOH relative to H2O2.
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RICO Flight 09
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RICO Flight 11 Peroxides
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Hydrogen Peroxide Hydrogen Peroxide Hydrogen Peroxide Hydrogen Peroxide Hydrogen Peroxide Hydrogen Peroxide Hydrogen Peroxide Hydrogen Peroxide Hydrogen Peroxide Hydrogen Peroxide
  RF03 RF03 RF03 RF04 RF04 RF04 RF11 RF11 RF11
Altitude, ft 1st 2nd delta 1st 2nd delta 1st 2nd delta
           
15000   300-550   250-300 250-300 0 1300 1250 -50
             
1500 600-700 1000-1200 400 900-1100 900-1100 0 1250 1650 400
             
300 500-700 900-1100 400 700-900 700-900 0 1050 1500 450
  180 in rain 400 in rain          
             
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Methyhydroperoxide Methyhydroperoxide Methyhydroperoxide Methyhydroperoxide Methyhydroperoxide Methyhydroperoxide Methyhydroperoxide Methyhydroperoxide Methyhydroperoxide Methyhydroperoxide
  RF03 RF03 RF03 RF04 RF04 RF04 RF11 RF11 RF11
Altitude, ft 1st 2nd delta 1st 2nd delta 1st 2nd delta
           
15000   100-150   50-160 50-160 0 250 150 -100
             
1500 550-650 500-600 -50 800-900 800-900 0 500 650 150
             
300 650 600 -50 700-800 700-800 0 600 700 100
  450 in rain 200 in rain          
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RF04 Cloud Sample Segment

• In/Out/In/Out... Clouds
• H2O2 1000 1800 CH3OOH 1000 1100
• H2O2 maximum at 2-3 km, 1500
• CH3OOH maximum a 1-2 km, 900

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Hypotheses to be tested

• H1 The aqueous phase gas-to-particle conversion
  is rapid enough in some clouds to substantially
  increase the amount of soluble material in cloud
  droplets, thus enhancing the activity of CCN upon
  evaporation.
• H2Cloud age, tauc, is constrained by chemical
  observations.
• H3 Free-troposphere marine-boundary-layer
  entrainment velocity, we, and cloud entrainment,
  epsilonc, are constrained by chemical
  observations.
• H4 The occurrence of recent precipitation in an
  air parcels history is detectable from
  observations of H2O2 and CH3OOH .

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Peroxide Measurements

• Gas phase measurements
• Air is sub-sampled with a forward facing diffuser
  style inlet. The gas phase peroxides are
  partitioned in to an aqueous collection solution
  in a concurrent-flow collection coil.
• Peroxides are separated via HPLC and quantified
  by post column derivatization to form a
  fluorescent dimmer.
• H2O2 and CH3OOH are separated in about 2 minutes
• Detection Limit for H2O2 is 15 pptv.
• Detection Limit for CH3OOH is 25 pptv.
• Counter-flow Virtual Impactor samples will also
  be analyzed for the peroxides.
• Determine peroxide content of cloudwater and
  precipitation.
• Examine the gas-aqueous phase partitioning of the
  peroxides.

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Gas phase Peroxide Measurements

• Gas phase peroxides will be collected from a
  forward facing diffuser style inlet.
• Peroxides are continuously partitioned in to an
  aqueous collection solution base on Henrys Law.
• The collection solution is sampled and injected
  in to an HPLC for peroxide separation and
  quantification.
• Collect a 30 second sample every 2 minutes
  minutes when operating two HPLC systems.

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Peroxide Analytical System

• Peroxides are separated on a C-18 column, and
  undergo a post column derivatization with
  p-hydroxyphenyl acetic acid to form a fluorescent
  dimmer.
• H2O2 and CH3OOH are separated in about 2 minutes
• Detection Limit for H2O2 is 15 pptv.
• Detection Limit for CH3OOH is 25 pptv.
• Samples from the CVI inlet will also be analyzed
  for the peroxides.

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Counterflow Virtual Impactor (CVI)

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• Cloud droplets (8-50 mm) are impacted into dry
  nitrogen gas and evaporated. Interstitial
  particles and gases excluded.
• Volatile gases and non-volatile residual
  particles are measured.

Lyman-a hygrometer
CCN Counter
Impactor Filters for Elec. Mic.
Optical Particle Counter
CN Counter
H2O2 sensor
From Twohy
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