The influence of boreal forest fires on the global distribution of NMHCs.

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1 The influence of boreal forest fires on the global distribution of NMHCs. Alastair Lewis, Mat Evans James Hopkins, Stephen Andrews, Shalini Punjabi, Jame Lee, Ruth Purvis, Lucy Carpenter + BORTAS science team

2 Drivers of NMHCs composition in background locations Natural emissions of NMHCs Terrestrial vegetation (isoprene, terpenes, others) Oceanic (alkenes) Biomass burning (many) Anthropogenic emissions of NMHCs Natural gas (nc 2, nc 3 ) Tailpipe (many) Evaporative (alkanes, aromatics)

3 Tracking anthropogenic emissions reductions UK ambient benzene UK emissions benzene Urban observation trends are driven by anthropogenic emissions reductions Other benzene sources.

4 o Background locations in GAW are impacted by a mix of local and distant sources including large changes in urban emissions and uncertain natural changes. o With the clear exception of isoprene, lifetimes of many hydrocarbons do allow for regional and LRT o What might an expanded GAW network tell us about trends in the various sources? o Which VOC sources dominate which species at which sites? o Any surprises? A case study

5 [acetylene] (pptv)

6 Measurement methods GC-FID Silcosteel canisters in aircraft hold Post-flight analysis Good for simple NMHCs, high precision Not suitable for polar or semi-volatile VOCs PTR-MS Soft ionisation, no spectra for unknowns Some key interferences e.g. isoprene, furan, GC-MS OVOCs, terpenes, nitriles etc Slow 180 secs

7 In-flight analysis highlights the mixtures Air chromatogram in flight, extracted ions from full scan mode Acetone Furan Toluene Furfural Xylenes Monoterpenes Tri/tetra MB Naphthalene Air chromatogram, full scan mode Selected ion monitoring mode

8 Biogenic hydrocarbon metrology Isoprene standards good and stable already. Monoterpene standards multi-component ppb mixtures available, uncertain stability Methanol, acetone, GLVs, PAH reliant on permeation, dilution methods, ad hoc

9 Safe sampling volumes as a function of flow rate Tenax trap 20 C

10 Peak area CO (ppb) Variability in other VOCs in and out of plumes B624A Benzene Toluene Furfural alpha pinene camphene limonene benzaldehyde benzonitrile acetophone camphor naphthalene CO /21/ :48 7/21/ :00 7/21/ :12 7/21/ :24 7/21/ : Time (GMT)

11 Functionalised species in mid-troposphere Model biomass CO prediction

12 Hydrocarbon relationships in above Canadian forests Enormous complexity of species Some emitted directly, some induced by burning process Background FT Biomass plumes [CO] (ppb)

13 Monoaromatics, acetone, methanol

14 Global average summertime benzene from biomass burning Uses annual GFED III fires CO:NMHC Emission Ratio data with tagged tracer hydrocarbon GEOSChem model Estimate the annual mean benzene and the mean for the highest mon

15 Biomass / anthropogenic fractional contribution

16 Shorter-lived alkenes

17 Model vs remote GAW benzene measurement Biomass burning + RETRO 2000 Cape Verde Atmospheric Observatory - mid Atlantic on line measurement Biomass burning RETRO 2000 Observations Biomass only

18 RETRO 2000 anthropogenic emissions may be too high RETRO 1/3 RETRO 0.33 x RETRO 2000 would fit better with the (very limited) data. Declining anthropogenic benzene of course increases the biomass fraction

19 How great an influence on GAW global stations?

20 Model comparison with the 25 GAW Global status stations Very few currently have any data, so this is a paper study

21 Likely biomass benzene fraction at GAW Global stations

22 Summary VOC network still inadequate - flask NMHCs tell only part of the story, more on-line measurements required GAW will track more than just anthropogenic changes, each site will need careful evaluation. Biomass burning contributions to certain NMHCs appears significant at many GAW stations. Natural background in benzene/naphthalene etc not clearly defi