Case Studies of OH and Gaseous Sulfur Compounds in Relation to Aerosol Particles in the Marine Atmosphere
Max Adam
Centre for Climate and Air Pollution Studies, School of Physics National University of Ireland Galway, Ireland
19/09/2013ACCENT-Plus Symposium
ACCENT-Plus Symposium 2
Mace Head Research Station
Mace Head
19/09/2013
• Global Atmosphere Watch (GAW) and EMEP Station
• Extensive Aerosol and GHG measurements
• Marine air sector from 190° - 300°
• Since 2010: OH, H2SO4, MSA(g), NO, NO2, J(O1D), J(NO2)
MSA(g) methane sulfonic acid, CH3SO3HJ(O1D) photolysis frequency of ozoneJ(NO2) photolysis frequency of nitrogen dioxide
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O(1D)
H
HCHO
CO
O(3P)
O3
H2O2
RO2
H2O
OH
X
SO2
CH2-CCl3
NH2
XO NO
HSO3 HS
H2SO4HNO3
HCl
HO2
NO
O3
multiplesteps multiple
steps
multiplesteps
multiplesteps
multiplesteps
other S-products
multiplesteps
HO2
Rain
M
O2,M
HXNO2
CH3CCl3
CH3SCH3
NH3
H2
CxHy
hh
h
H2O
O2,M
Aerosol
AerosolRain
AerosolRain
H2SSO2
HCFC
CO,CH4
HX = HCl, HF, HBr, HICxHy = Hydrocarbons
Atmospheric Oxidation Efficiency
OH Primary Production
Ozone Photolysis 340 nm
J(O1D) = Photolysis Frequency, s-1 Formation of O(1D) by UV-B Proxy for UV-B
O3 + h O(1D) + O2
O(1D) + H2O 2 OH
J(O1D)
OH :
Most important oxidant (chemical detergent) of the atmosphere !
Main Consumption:
Reactions with Methane (CH4), Carbon Monoxide (CO)
(OH) 1 sec
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Chemical Ionisation Mass Spectrometer (CIMS)
OH H2SO4
MSA(g)
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[OH] = m/z 99, Signal– Background
Signal (Mass 99) = Ambient OH + 34SO2 H34SO4-
Background (Mass 99) = Ambient OH + 34SO2 + OH Scavenger (Propane)
Chemical Ionisation Mass Spectrometer (CIMS)
[MSA] = m/z 95
Reagent Ion = NO3- (Mass 62)
[H2SO4] = m/z 97 30 sec measurements
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Measurement Principle for OH, H2SO4 and MSA (g)
Det. Limits (2σ, 5min): OH = 1.3 x 105 molec cm-3
H2SO4, MSA = 4.3 x 104 molec cm-3
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Location of CIMS and Radiometers
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1. J(O1D): A Proxy for OH
Berresheim, H., et al. (2013), Geophys. Res. Lett., 40, 1659–1663 Rohrer, F. and Berresheim, H. (2006), Nature, 442, 184-187
• No tidal cycle relation.
Results
Marine Air (NO<50 pptv)
• Strong OH - J(O1D) correlation (R = 0.75)
ACCENT-Plus Symposium 8 19/09/2013
Mid-day Maxima of H2SO4 and MSA(g) in Marine Air Mace Head, Ireland (10-14 UTC; 05/2010 - 08/2012)
2a. H2SO4 and MSA (g) - Time Series
ACCENT-Plus Symposium 9 19/09/2013
Monthly Mean Aerosol MSA(a) and Non-Sea Salt Sulfate Concentrations in Marine Air Mace Head, Ireland
2a. MSA(a) and nss-SO4 - Time Series
Ovadnevaite, J. et al., manuscript in prep., 2013
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• Total SO2 Measurement Period: 02 May 2011 – 12 August 2011
• Marine SO2 Average Mixing Ratio = 163 (± 58) pptv
SO2 Measurements (Thermo 43i)
2b. H2SO4 - Mass Balance
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2b. Mass Balance
[H2SO4]calc=
• Case study of measured vs. calculated H2SO4 on 05 June 2011.
CS = Aerosol Condensational Sink for H2SO4
k OH [ SO 2 ] [OH ]CS
• Discrepancy by a factor of 3.5 is observed.
3.5
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k OH [ SO 2 ] [OH ]+k X [SO 2 ] [X ]CS
2c. Mass Balance with X-Compound
[H2SO4]calc=
1Mauldin, R.L., et al. (2012), Nature, 488, 193-196.
• Case study of measured vs. calculated H2SO4 on 05 June 2011.
CS = Aerosol Condensational Sink for H2SO4
• Discrepancy by a factor of 3.5 is observed.
• Presence of another oxidant ‘X’ that oxidises SO2 to H2SO4.
• sCI (from α-pinene, limonene + O3)1, halogen (BrO, ClO, IO, OIO), or NO3 radicals found to be unlikely candidates for ‘X’ .
A major missing oxidant for SO2 !
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Schematic of front inlet
Amplification factor = for Criegees in CIMS
[ ] [ ]
[ ]amb cims
amb
sCI sCIAF
sCI
= 3.25
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3. MSA – Gas Particle Partitioning
• Nighttime peak MSA(g) mixing ratios – support general anti-correlation of MSA(g) with relative humidity.
1De Bruyn, W.J., et al. (1994), J. Geophys. Res., 99, 16927-16932.
• MSA(g) - low lifetime with respect to aerosol uptake (1/CS) of 31.7 min assuming a sticking coefficient alpha (α) = 0.121
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Conclusions
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• OH shows a robust relationship with J(O1D) but has no relation to tide.
• H2SO4 balance: Calculation based only on SO2+OH source underestimates observed H2SO4 by factor 4.2 (on average).
• Evidence for presence of an unknown oxidant X from OH background measurements. Criegees (α-pinene, limonene + O3) are unlikely candidates.
• MSA partitions back to gas phase with rH decreasing. Caution with respect to using average aerosol MSA/nss-SO4 ratio for calculating biogenic nss-SO4 fraction.
16
Elevated Background, Case 2: 9th June 2011
Thank You!
Acknowledgements
H. Berresheim (NUI, Galway)
F. Rohrer (Research Center Jülich, Germany)B. Bohn (Research Center Jülich, Germany)
C. Monahan (NUI, Galway)C. O‘Dowd (NUI, Galway)
J. Ovadnevaite (NUI, Galway)J. M. C. Plane (Univ. of Leeds, UK)
Sponsors: SFI, EPA – Ireland
19/09/2013ACCENT-Plus Symposium
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