Summertime tropospheric observations related to N x O y distributions and partitioning over Alaska: Arctic Boundary Layer Expedition 3A

Measurements of the reactive odd nitrogen compounds NO, NO 2 , 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 O 3 , CO, C 2 H 2 , C 2 H 6 , C 3 H 8 , C 2 Cl 4 , and H 2 O 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 + NO 2 ) 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 (∼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 altitudes in the vicinity of the tropopause as a major contributor to the abundance of NO y , (∼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).