Summertime tropospheric observations related to N_x O_y distributions and partitioning over Alaska: Arctic Boundary Layer Expedition 3A

Abstract

Measurements of the reactive odd nitrogen compounds NO, NO2, peroxyacetyl nitrate (PAN), and NOy 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 NxOy, 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 NOx (NO + NO2) were nearly independent of altitude, having values of about 8.5 and 25 pptv, respectively. Median mixing ratios of NOy varied from about 350 pptv within the lowest altitudes to about 600 pptv within the highest altitudes sampled. PAN constituted the largest fraction of NOy (∼50%) at the highest altitudes. In addition, PAN mixing ratios accounted for all of the approximate 60 pptv/km altitudinal dependency in NOy. The analyses presented implicate biomass burning in Siberia as the probable source of about one‐third of the NOy 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 NOy, (∼30–50%) within the lower 6‐km column over Alaska. However, the exact origin of this high‐altitude NOy 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).

Comparison of free tropospheric western Pacific air mass classification schemes for the PEM‐West A experiment

“…This pair of compounds has yielded usefid information about the relative degrees to which different air masses have been processed within the atmosphere overlying remote regions [e.g., Sandholm et al, 1992]. Over the western Pacific the mixing ratios of C2H • and C3H8 were correlated with the observed ratio C2H2/CO (Figures 2a and 2b) as might be expected based on the relative photochemical processing time relationship described above.…”

Influence of plumes from biomass burning on atmospheric chemistry over the equatorial and tropical South Atlantic during CITE 3

“…They are also at the high end of the range of values found in boreal/taiga fire plumes during ABLE 3A and ABLE 3B: ANOr/ACO • 0.02-0.04 100 Concentrations in ppt [Sandholm et al, 1992[Sandholm et al, , 1994[Sandholm et al, 1992[Sandholm et al, , 1994…”

Photofragmentation two‐photon laser‐induced fluorescence detection of NO2 and NO: Comparison of measurements with model results based on airborne observations during PEM‐Tropics A

“…Several different versions of this system have been used for NO and NO 2 measurements for over a decade [Bradshaw et al, 1985;Davis et al, 1987;Sandholm et al, 1990Sandholm et al, , 1992Sandholm et al, , 1997. The current version differs from the earlier ones both in having substantially improved sensitivity and in having a highly modified sample inlet.…”