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

McDuffie, Erin E.; Womack, Caroline C.; Fibiger, Dorothy L.; Dube, William P.; Franchin, Alessandro; Middlebrook, Ann M.; Goldberger, Lexie; Lee, Ben H.; Thornton, Joel A.; Moravek, Alexander; Murphy, Jennifer G.; Baasandorj, Munkhbayar; Brown, Steven S.

Mountain basins in Northern Utah, including the Salt Lake Valley (SLV), suffer from wintertime air pollution events associated with stagnant atmospheric conditions. During these events, fine particulate matter concentrations (PMinline-formula2.5) can exceed national ambient air quality standards. Previous studies in the SLV have found that PMinline-formula2.5 is primarily composed of ammonium nitrate (inline-formulaNH4NO3), formed from the condensation of gas-phase ammonia (inline-formulaNH3) and nitric acid (inline-formulaHNO3). Additional studies in several western basins, including the SLV, have suggested that production of inline-formulaHNO3 from nocturnal heterogeneous inline-formulaN2O5 uptake is the dominant source of inline-formulaNH4NO3 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 wintertime pollution events in the SLV. Coupled with ground-based observations, analyses of day- and nighttime research flights confirm that PMinline-formula2.5 during wintertime pollution events is principally composed of inline-formulaNH4NO3, limited by inline-formulaHNO3. Here, observations and box model analyses assess the contribution of inline-formulaN2O5 uptake to nitrate aerosol during pollution events using the inline-formula M13inlinescrollmathml chem normal NO normal 3 - 25pt16ptsvg-formulamathimg9712381780fcc4de6c4d72f703a8771c acp-19-9287-2019-ie00001.svg25pt16ptacp-19-9287-2019-ie00001.png production rate, inline-formulaN2O5 heterogeneous uptake coefficient (inline-formulaγ(N2O5)), and production yield of inline-formulaClNO2 (inline-formulaφ(ClNO2)), which had medians of 1.6 inline-formulaµg minline-formula−3 hinline-formula−1, 0.076, and 0.220, respectively. While fit values of inline-formulaγ(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 inline-formulaN2O5 uptake produces between 2.4 and 3.9 inline-formulaµg minline-formula−3 of nitrate per day when considering the possible effects of dilution. This nocturnal production is sufficient to account for 52 %–85 % of the daily observed surface-level buildup of aerosol nitrate, though accurate quantification is dependent on modeled dilution, mixing processes, and photochemistry.



McDuffie, Erin E. / Womack, Caroline C. / Fibiger, Dorothy L. / et al: On the contribution of nocturnal heterogeneous reactive nitrogen chemistry to particulate matter formation during wintertime pollution events in Northern Utah. 2019. Copernicus Publications.


Rechteinhaber: Erin E. McDuffie et al.

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