1. 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

2. Mace Head Research Station Mace Head 19/09/2013ACCENT-Plus Symposium Global Atmosphere Watch (GAW) and EMEP Station Extensive Aerosol and GHG measurements Marine air sector from 190° - 300° Since 2010: OH, H 2 SO 4, MSA(g), NO, NO 2, J(O 1 D), J(NO 2 ) 2 MSA(g)methane sulfonic acid, CH 3 SO 3 H J(O 1 D) photolysis frequency of ozone J(NO 2 ) photolysis frequency of nitrogen dioxide

3. Atmospheric Oxidation Efficiency OH Primary Production Ozone Photolysis  340 nm J(O 1 D) = Photolysis Frequency, s -1 Formation of O( 1 D) by UV-B Proxy for UV-B O 3 + h O( 1 D) + O 2 O( 1 D) + H 2 O 2 OH J(O 1 D) OH : Most important oxidant (chemical detergent) of the atmosphere ! Main Consumption: Reactions with Methane (CH 4 ), Carbon Monoxide (CO)  (OH)  1 sec 19/09/2013ACCENT-Plus Symposium3

4. 19/09/2013ACCENT-Plus Symposium Chemical Ionisation Mass Spectrometer (CIMS) OH H 2 SO 4 MSA(g) 4

5. [OH] = m/z 99, Signal– Background Signal (Mass 99) = Ambient OH + 34 SO 2 H 34 SO 4 - Background (Mass 99) = Ambient OH + 34 SO 2 + OH Scavenger (Propane) Chemical Ionisation Mass Spectrometer (CIMS) [MSA] = m/z 95 Reagent Ion = NO 3 - (Mass 62) [H 2 SO 4 ] = m/z 9730 sec measurements 19/09/2013ACCENT-Plus Symposium Measurement Principle for OH, H 2 SO 4 and MSA (g) Det. Limits (2σ, 5min): OH = 1.3 x 10 5 molec cm -3 5 H 2 SO 4, MSA = 4.3 x 10 4 molec cm -3

6. Location of CIMS and Radiometers 19/09/2013ACCENT-Plus Symposium6

7. 19/09/2013ACCENT-Plus Symposium 1. J(O 1 D): 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) 7 Strong OH - J(O 1 D) correlation (R = 0.75)

8. 19/09/2013ACCENT-Plus Symposium Mid-day Maxima of H 2 SO 4 and MSA(g) in Marine Air Mace Head, Ireland (10-14 UTC; 05/2010 - 08/2012) 2a. H 2 SO 4 and MSA (g) - Time Series 8

9. 19/09/2013ACCENT-Plus Symposium9 Monthly Mean Aerosol MSA(a) and Non-Sea Salt Sulfate Concentrations in Marine Air Mace Head, Ireland 2a. MSA(a) and nss-SO 4 - Time Series Ovadnevaite, J. et al., manuscript in prep., 2013

10. 19/09/2013ACCENT-Plus Symposium Total SO 2 Measurement Period: 02 May 2011 – 12 August 2011 Marine SO 2 Average Mixing Ratio = 163 (± 58) pptv SO 2 Measurements (Thermo 43i) 2b. H 2 SO 4 - Mass Balance 10

11. 19/09/2013ACCENT-Plus Symposium11 2b. Mass Balance [H 2 SO 4 ] calc = Case study of measured vs. calculated H 2 SO 4 on 05 June 2011. CS = Aerosol Condensational Sink for H 2 SO 4 Discrepancy by a factor of 3.5 is observed. 3.5

12. 19/09/2013ACCENT-Plus Symposium 2c. Mass Balance with X-Compound [H 2 SO 4 ] calc = 1 Mauldin, R.L., et al. (2012), Nature, 488, 193-196. Case study of measured vs. calculated H 2 SO 4 on 05 June 2011. CS = Aerosol Condensational Sink for H 2 SO 4 12 Discrepancy by a factor of 3.5 is observed. Presence of another oxidant ‘X’ that oxidises SO 2 to H 2 SO 4. sCI (from α-pinene, limonene + O 3 ) 1, halogen (BrO, ClO, IO, OIO), or NO 3 radicals found to be unlikely candidates for ‘X’. A major missing oxidant for SO 2 !

13. 19/09/2013ACCENT-Plus Symposium13 Schematic of front inlet Amplification factor = for Criegees in CIMS = 3.25

14. 19/09/2013ACCENT-Plus Symposium 3. MSA – Gas Particle Partitioning Nighttime peak MSA(g) mixing ratios – support general anti-correlation of MSA(g) with relative humidity. 1 De Bruyn, W.J., et al. (1994), J. Geophys. Res., 99, 16927-16932. 14 MSA(g) - low lifetime with respect to aerosol uptake (1/CS) of 31.7 min assuming a sticking coefficient alpha (α) = 0.12 1

15. Conclusions 19/09/2013ACCENT-Plus Symposium OH shows a robust relationship with J(O 1 D) but has no relation to tide. 15 H 2 SO 4 balance: Calculation based only on SO 2 +OH source underestimates observed H 2 SO 4 by factor 4.2 (on average). Evidence for presence of an unknown oxidant X from OH background measurements. Criegees (α-pinene, limonene + O 3 ) are unlikely candidates. MSA partitions back to gas phase with rH decreasing. Caution with respect to using average aerosol MSA/nss- SO 4 ratio for calculating biogenic nss-SO 4 fraction.

16. Elevated Background, Case 2: 9 th June 2011 16 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 19/09/2013 ACCENT-Plus Symposium