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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. Mace Head Research Station. Mace Head.

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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

ACCENT-Plus Symposium

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Mace Head Research Station

Mace Head

  • 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, CH3SO3H

J(O1D) photolysis frequency of ozone

J(NO2) photolysis frequency of nitrogen dioxide

ACCENT-Plus Symposium

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Atmospheric Oxidation Efficiency

OH Primary Production

Ozone Photolysis  340 nm

J(O1D)

O3 + h O(1D) + O2

O(1D) + H2O 2 OH

J(O1D) = Photolysis Frequency, s-1 Formation of O(1D) by UV-B Proxy for UV-B

OH :

Most important oxidant (chemical detergent) of the atmosphere !

Main Consumption:

Reactions with Methane (CH4), Carbon Monoxide (CO)

 (OH)  1 sec

ACCENT-Plus Symposium

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Chemical Ionisation Mass Spectrometer (CIMS)

OH

H2SO4

MSA(g)

ACCENT-Plus Symposium

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Chemical Ionisation Mass Spectrometer (CIMS)

Measurement Principle for OH, H2SO4 and MSA (g)

Signal (Mass 99) = Ambient OH + 34SO2 H34SO4-

Background (Mass 99) = Ambient OH + 34SO2 + OH Scavenger (Propane)

Reagent Ion = NO3- (Mass 62)

[OH] = m/z 99, Signal– Background

[H2SO4] = m/z 97

30 sec measurements

[MSA] = m/z 95

Det. Limits (2σ, 5min): OH = 1.3 x 105molec cm-3

H2SO4, MSA = 4.3 x 104molec cm-3

ACCENT-Plus Symposium

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Results

1. J(O1D): A Proxy for OH

Marine Air (NO<50 pptv)

  • Strong OH - J(O1D) correlation (R = 0.75)
  • No tidal cycle relation.

Berresheim, H., et al. (2013), Geophys. Res. Lett.,40, 1659–1663

Rohrer, F. and Berresheim, H. (2006), Nature, 442, 184-187

ACCENT-Plus Symposium

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2a. H2SO4 and MSA (g) - Time Series

Mid-day Maxima of H2SO4 and MSA(g) in Marine Air

Mace Head, Ireland (10-14 UTC; 05/2010 - 08/2012)

ACCENT-Plus Symposium

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2a. MSA(a) and nss-SO4 - Time Series

Monthly Mean Aerosol MSA(a) and Non-Sea Salt Sulfate Concentrations in Marine Air Mace Head, Ireland

Ovadnevaite, J. et al., manuscript in prep., 2013

ACCENT-Plus Symposium

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2b. H2SO4 - Mass Balance

SO2 Measurements (Thermo 43i)

  • Total SO2 Measurement Period: 02 May 2011 – 12 August 2011
  • Marine SO2 Average Mixing Ratio = 163 (± 58)pptv

ACCENT-Plus Symposium

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2b. Mass Balance

CS = Aerosol Condensational Sink for H2SO4

[H2SO4]calc=

3.5

  • Case study of measured vs. calculated H2SO4on 05 June 2011.
  • Discrepancy by a factor of 3.5 is observed.

ACCENT-Plus Symposium

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2c. Mass Balance with X-Compound

CS = Aerosol Condensational Sink for H2SO4

[H2SO4]calc=

  • Case study of measured vs. calculated H2SO4on 05 June 2011.
  • 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 beunlikely candidates for ‘X’ .
  • A major missing oxidant for SO2 !

1Mauldin, R.L., et al. (2012), Nature, 488, 193-196.

ACCENT-Plus Symposium

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Schematic of front inlet

= 3.25

Amplification factor =

for Criegees in CIMS

ACCENT-Plus Symposium

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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.
  • MSA(g)- low lifetime with respect to aerosol uptake (1/CS) of 31.7 min assuming a sticking coefficient alpha (α) = 0.121

1De Bruyn, W.J., et al. (1994), J. Geophys. Res., 99, 16927-16932.

ACCENT-Plus Symposium

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Conclusions

  • OH shows a robust relationship with J(O1D) but has no relation to tide.
  • H2SO4balance: 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.

ACCENT-Plus Symposium

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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

Elevated Background, Case 2:

9th June 2011

ACCENT-Plus Symposium