Ally Lewis, University of York, U.K Data from Katie Read, Jim Hopkins, Jacqui Hamilton.

1. Ally Lewis, University of York, U.K • Data from Katie Read, Jim Hopkins, Jacqui Hamilton. • NMHCs, & DMS measurements by GC-FID • Remote automated NMHC, - simple robust instrument. • Addition of OVOC measurements – 2 columns / detectors

2. Long term NMHC measurements: Halley Antarctic • CASLab, British Antarctic Survey Halley Base, Antarctica • Year round NMHC • 2005 Jan-Mar O3 / HOx experiment

3. Seasonal distribution of alkanes at Halley, Antarctica

4. OH dependence of ethane and propane concentrations Deviation • From previous work the seasonal trend should follow a sinusoidal oscillation1,2,3, this work showed a deviation in early Spring, particularly for ethane. • OH chemistry is not thought to be significant at this time. • Could potentially be an influence of Cl chemistry over this period? • 1Sharma, U. K., Y. Kajii, et al. (2000). "Seasonal variation of C2-C6 NMHCs at Happo, a remote site in Japan." Atmos. Env.34: 447-4458. • 2Swanson, A. L., N. Blake, et al. (2003). "Seasonal variations of C1-C4 nonmethane hydrocarbons and C1-C4 alkyl nitrates at the Summit research station in Greenland." J. Geophys. Res108(D2): 4065, doi:10.1029/2001JD001445. • 3Clarkson, T. S., R. J. Martin, et al. (1997). "Ethane and propane in the southern marine troposphere." Atmos. Environ.31(22): 3763-3771.

5. Halogen atom presence during NMHC and O3 depletion episodes • Used the behaviour of NMHC and Cl kinetics to determine the [Cl] (and [Br] during periods of ozone depletion1 • [RH]LO = [RH]BKG exp(-kCl∫[Cl]dt) • A plot of ln([RH]LO/[RH]BKG should give a linear relationship with a gradient equal to -∫[Cl]dt. • So by integrating over set time periods we can obtain [Cl]. • [Br] can also be calculated from the additional ethene and acetylene removal. • [-kBr ∫[Br]dt =ln([C2H2]LO/[C2H2]BKG)observed-ln([C2H2]LO/[C2H2]BKG)Clatom • For this depletion period this analysis gives a [Cl] of between 1.7 x 103 and 3.4 x 104 atom cm-3 and a [Br] of between 1.4 x 106 to 2.9 x 107 atom cm-3 . • 1Jobson, B. T., H. Niki, et al. (1994)."Measurements of C2-C6 hydrocarbons during the Polar Sunrise 1992 Experiment: Evidence for Cl atom and Br atom chemistry." J. Geophys. Res99(D12): 25355-25368.

6. Cl atom presence during early spring • CO remained high during September whilst the O3 and ethane decreased. • We can apply the same analysis as with the ozone depletion episodes for this austral spring period. • The gradient of:- • ln ([HC] t =2 weeks/[HC] t=0) vs kHC+Cl • implied NMHC reactions with a persistent [Cl] of 2.3 x 103 atom cm-3 over a two week period. 3 x 103 atom cm-3 Cl atom input into GEOS-CHEM model for just 15 days1 ethane-black line GEOS-CHEM model-blue line 1Mat Evans and Sarah Walker- School of Earth and Environment (SEE), University of Leeds

7. NMHC + OVOC in background N Atlantic air Measurements by GC-2xFID C2-C7 NMHCs + DMS Mace Head , West coast Ireland acetaldehyde acetone ethanol Methanol benzene methacrolien MVK

8. 18 35 Time / mins 8 • Sum NMHC=All NMHC except ethane. • Sum O-VOC=Acetone + Acetaldehyde + Methanol + Methacrolein concentrations. • Only in periods of anticyclonic + local easterly pollution does the mass sum of the NMHC compare to the sum of the O-VOC. 30 10 Time / mins

9. Combining NMHCs, methanol and DMS

10. Simulating wind speed dependence of measurements Calculated ocean uptake rate varied from 0.03 to 0.19 cm s-1 depending upon the wind speed. [Global vD of 0.1 cm s-1 estimated by Singh et al. (2002)]

11. Isoprene and degradation products during summer 2003