Seasonal variability of atmospheric nitrogen oxides and non-methane hydrocarbons at the GEOSummit station, Greenland

摘要

Measurements of atmospheric nitrogen oxides NO(NO = NO + NO), peroxyacetyl nitrate (PAN), NO,and non-methane hydrocarbons (NMHC) were taken at the Greenland Environmental Observatory at Summit (GEOSummit) station,Greenland (72.34° N, 38.29° W; 3212 m a.s.l.), fromJuly 2008 to July 2010. The data set represents the first year-roundconcurrent record of these compounds sampled at a high latitude Arctic site.Here, the study focused on the seasonal variability of these important ozone(O) precursors in the Arctic troposphere and the impact from transportedanthropogenic and biomass burning emissions. Our analysis shows that PAN isthe dominant NO species in all seasons at Summit, varying from 42 to76 %; however, we find that odd NO species (oddNO = NO − PAN − NO) contribute a largeamount to the total NO speciation. We hypothesize that the source of thisodd NO is most likely alkyl nitrates and nitric acid (HNO) fromtransported pollution, and photochemically produced species such as nitrous acid (HONO).FLEXPART retroplume analyses and black carbon (BC) tracers for anthropogenicand biomass burning (BB) emissions were used to identify periods when thesite was impacted by polluted air masses. Europe contributed the largestsource of anthropogenic emissions during the winter months (November–March)with 56 % of the total anthropogenic BC tracer originating from Europe in2008–2009 and 69 % in 2009–2010. The polluted plumes resulted in meanenhancements above background levels up to 334, 295, 88, and1119 pmol mol for NO, PAN, NO, and ethane, respectively,over the two winters. Enhancements in O precursors during the secondwinter were typically higher, which may be attributed to the increase inEuropean polluted air masses transported to Summit in 2009–2010 compared to2008–2009. O levels were highly variable within the sampled anthropogenicplumes with mean ΔO levels ranging from −6.7 to7.6 nmol mol during the winter periods.North America was the primary source of biomass burning emissions during thesummer; however, only 13 BB events were observed as the number of air massestransported to Summit, with significant BB emissions, was low in generalduring the measurement period. The BB plumes were typically very aged, withmedian transport times to the site from the source region of 14 days. Theanalyses of O and precursor levels during the BB events indicatethat some of the plumes sampled impacted the atmospheric chemistry at Summit,with enhancements observed in all measured species.