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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Mar 2019

Research article | 15 Mar 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

On the contribution of nocturnal heterogeneous reactive nitrogen chemistry to particulate matter formation during wintertime pollution events in Northern Utah

Erin E. McDuffie1,2,3,a, Caroline Womack1,2, Dorothy L. Fibiger1,2,b, William P. Dube1,2, Alessandro Franchin1,2, Ann Middlebrook1, Lexie Goldberger4,c, Ben H. Lee4, Joel A. Thornton4, Alexander Moravek5, Jennifer Murphy5, Munkhbayar Baasandorj6,d, and Steven S. Brown1,3 Erin E. McDuffie et al.
  • 1Chemical Sciences Division, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 3Department of Chemistry, University of Colorado, Boulder, CO, USA
  • 4Department of Atmospheric Science, University of Washington, Seattle, WA, USA
  • 5Department of Chemistry, University of Toronto, Toronto, Canada
  • 6Department of Atmospheric Sciences, University of Utah, Salt Lake City, UT, USA
  • anow at: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada
  • bnow at: California Air Resources Board, Sacramento, CA, USA
  • cnow at: ARM Aerial Facility, Pacific Northwest National Laboratory, Richland, WA, USA
  • dnow at: Chevron Corporation, Houston, TX, USA

Abstract. Mountain basins in Northern Utah, including Salt Lake Valley (SLV), suffer from wintertime air pollution events associated with stagnant atmospheric conditions. During these events, fine particulate matter concentrations (PM2.5) can exceed national ambient air quality standards. Previous studies in SLV have found PM2.5 is primarily composed of ammonium nitrate (NH4NO3), formed from the condensation of gas-phase ammonia (NH3) and nitric acid (HNO3). Additional studies in several western basins, including SLV, have suggested that production of HNO3 from nocturnal heterogeneous N2O5 uptake is the dominant source of NH4NO3 during winter. The rate of this process, however, remains poorly quantified, in part due to limited vertical measurements above the surface, where this chemistry is most active. The 2017 Utah Winter Fine Particulate Study (UWFPS) provided the first aircraft measurements of detailed chemical composition during SLV wintertime pollution events. Coupled with ground-based observations, analysis of day and nighttime research flights confirm that PM2.5 during wintertime pollution events is principally composed of NH4NO3, limited by HNO3. Here, observations and box-model analyses assess the contribution of N2O5 uptake to nitrate aerosol during pollution events using the NO3 production rate, N2O5 heterogeneous uptake coefficient (γ(N2O5)), and production yield of ClNO2 (Φ(ClNO2)), which had medians of 1.6 μg m−3 hr−1, 0.076, and 0.220, respectively. While fit values of γ(N2O5) may be biased high by a potential under-measurement in aerosol surface area, other fit quantities are unaffected. Lastly, additional model simulations suggest nocturnal N2O5 uptake produces 3.9 μg m−3 of nitrate per day, when considering the possible effects of dilution. This nocturnal production is sufficient to account for 86 % of the daily observed surface-level build-up of aerosol nitrate, though accurate quantification is dependent on modeled dilution and mixing processes.

Erin E. McDuffie et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Erin E. McDuffie et al.
Erin E. McDuffie et al.
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Publications Copernicus
Short summary
Populated mountain basins, including Salt Lake Valley (SLV), Utah, suffer from wintertime stagnation events that trap emissions near the surface and cause particulate matter (PM2.5) concentrations to reach unhealthy levels. Previously limited by a lack of nighttime measurements, this study uses 2017 UWFPS aircraft campaign data, in combination with a box model, to show that nitrogen chemistry occurring above the surface at night is the dominant source of PM2.5 during a wintertime event in SLV.
Populated mountain basins, including Salt Lake Valley (SLV), Utah, suffer from wintertime...