SUMMERTIME TROPOSPHERIC OBSERVATIONS RELATED TO NXOY DISTRIBUTIONS AND PARTITIONING OVER ALASKA - ARCTIC BOUNDARY-LAYER EXPEDITION 3A

Measurements of the reactive odd nitrogen compounds NO. NO2, peroxyacetyl nitrate (PAN), and NO(y) are presented for the summertime middle/lower troposphere (6.1-0.15 km) over northern high latitudes. In addition, the chemical signatures revealed from concurrent measurements of O3, CO, C2H2, C2H6, C3H8, C2Cl4, and H2O are used to further characterize factors affecting the budget and distribution of N(x)O(y) in the Arctic and sub-Arctic tropospheric air masses sampled over Alaska during the NASA Arctic Boundary Layer Expedition (ABLE 3A) field campaign. Many of the compounds listed above exhibited a general trend of median mixing ratios increasing in proportion with altitude within the lower 6-km column. However, median mixing ratios of NO and NO(x) (NO + NO2) were nearly independent of altitude, having values of about 8.5 and 25 pptv, respectively. Median mixing ratios of NO(y) varied from about 350 pptv within the lowest altitudes to about 600 pptv within the highest altitudes sampled. PAN constituted the largest fraction of NO(y) (approximately 50%) at the highest altitudes. In addition, PAN mixing ratios accounted for all of the approximate 60 pptv/km altitudinal dependency in NO(y). The analyses presented implicate biomass burning in Siberia as the probable source of about one-third of the NO(y) abundance within the middle/lower troposphere over Alaska. These analyses also implicate the downward transport of air from attitudes in the vicinity of the tropopause as a major contributor to the abundance of NO(y) (approximately 30-50%) within the lower 6-km column over Alaska. However, the exact origin of this high-altitude NO(y) remains uncertain. The impact of lower latitude industrial/urban pollution also remains largely uncertain, although various chemical signatures imply inputs from these regions would have been relatively well aged (15-30 days).