Dynamics of ozone and nitrogen oxides at Summit, Greenland. II. Simulating snowpack chemistry during a spring high ozone event with a 1-D process-scale model

Document Type

Article

Publication Date

9-1-2015

Abstract

© 2015 Elsevier Ltd. Observed depth profiles of nitric oxide (NO), nitrogen dioxide (NO < inf> 2 ), and ozone (O < inf> 3 ) in snowpack interstitial air at Summit, Greenland were best replicated by a 1-D process-scale model, which included (1) geometrical representation of snow grains as spheres, (2) aqueous-phase chemistry confined to a quasi-liquid layer (QLL) on the surface of snow grains, and (3) initialization of the species concentrations in the QLL through equilibrium partitioning with mixing ratios in snowpack interstitial air. A comprehensive suite of measurements in and above snowpack during a high O < inf> 3 event facilitated analysis of the relationship between the chemistry of snowpack and the overlying atmosphere. The model successfully reproduced 2 maxima (i.e., a peak near the surface of the snowpack at solar noon and a larger peak occurring in the evening that extended down from 0.5 to 2 m) in the diurnal profile of NO < inf> 2 within snowpack interstitial air. The maximum production rate of NO < inf> 2 by photolysis of nitrate (NO < inf> 3 < sup> - ) was approximately 10 < sup> 8 molec cm < sup> -3 s < sup> -1 , which explained daily observations of maxima in NO < inf> 2 mixing ratios near solar noon. Mixing ratios of NO < inf> 2 in snowpack interstitial air were greatest in the deepest layers of the snowpack at night and were attributed to thermal decomposition of peroxynitric acid, which produced up to 10 < sup> 6 molec NO < inf> 2 cm < sup> -3 s < sup> -1 . Highest levels of NO in snowpack interstitial air were confined to upper layers of the snowpack and observed profiles were consistent with photolysis of NO < inf> 2 . Production of nitrogen oxides (NO < inf> x ) from NO < inf> 3 < sup> - photolysis was estimated to be two orders of magnitude larger than NO production and supports the hypothesis that NO < inf> 3 < sup> - photolysis is the primary source of NO < inf> x within sunlit snowpack in the Arctic. Aqueous-phase oxidation of formic acid by O < inf> 3 resulted in a maximum consumption rate of ~10 < sup> 6 -10 < sup> 7 molec cm < sup> -3 s < sup> -1 and was the primary removal mechanism for O < inf> 3 .

Publication Title

Atmospheric Environment

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