Preprints
https://doi.org/10.5194/acp-2021-310
https://doi.org/10.5194/acp-2021-310

  18 May 2021

18 May 2021

Review status: this preprint is currently under review for the journal ACP.

Urban inland wintertime N2O5 and ClNO2 influenced by snow-covered ground, air turbulence, and precipitation

Kathryn D. Kulju1, Stephen M. McNamara1, Qianjie Chen1,a, Jacinta Edebeli1,2, Jose D. Fuentes3, Steven B. Bertman4, and Kerri A. Pratt1,5 Kathryn D. Kulju et al.
  • 1Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
  • 2Paul Scherrer Institut, 5232 Villigen, Switzerland
  • 3Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, Pennsylvania 16802, USA
  • 4Institute of the Environment and Sustainability, Western Michigan University, Kalamazoo, Michigan 49008, USA
  • 5Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA
  • acurrent address: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, China

Abstract. The atmospheric multiphase reaction of dinitrogen pentoxide (N2O5) with chloride-containing aerosol particles produces nitryl chloride (ClNO2), which has been observed across the globe. The photolysis of ClNO2 produces chlorine radicals and nitrogen dioxide (NO2), which alter pollutant fates and air quality. However, the effects of local meteorology on near-surface ClNO2 production are not yet well understood, as most observational and modeling studies focus on periods of clear conditions. During a field campaign in Kalamazoo, Michigan from January–February 2018, N2O5 and ClNO2 were measured using chemical ionization mass spectrometry, with simultaneous measurements of atmospheric particulate matter and meteorological parameters. We examine the impacts of atmospheric turbulence, precipitation (snow, rain) and fog, and ground cover (snow-covered and bare ground) on the abundances of ClNO2 and N2O5. N2O5 mole ratios were lowest during periods of lower turbulence and were not statistically significantly different between snow-covered and bare ground. In contrast, ClNO2 mole ratios were highest, on average, over snow-covered ground, due to saline snowpack ClNO2 production. Both N2O5 and ClNO2 mole ratios were lowest, on average, during rainfall and fog because of scavenging, with N2O5 scavenging by fog droplets likely contributing to observed increased particulate nitrate concentrations. These observations, specifically those during active precipitation and with snow-covered ground, highlight important processes, including N2O5 and ClNO2 wet scavenging, fog nitrate production, and snowpack ClNO2 production, that govern the variability in observed atmospheric chlorine and nitrogen chemistry and are missed when considering only clear conditions.

Kathryn D. Kulju et al.

Status: open (until 13 Jul 2021)

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Kathryn D. Kulju et al.

Kathryn D. Kulju et al.

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Short summary
N2O5 uptake by chloride-containing surfaces produces ClNO2, which photolyzes producing NO2 and highly reactive Cl radicals that impact air quality. In the inland urban atmosphere, ClNO2 was elevated during lower air turbulence and over snow-covered ground, from snowpack ClNO2 production. N2O5 and ClNO2 levels were lowest, on average, during rainfall and fog because of scavenging, with N2O5 scavenging by fog droplets likely contributing to observed increased particulate nitrate concentrations.
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