Abstract. 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 (PM2.5) can exceed national ambient air quality
standards. Previous studies in the SLV have found that 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 the 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 wintertime pollution events in the SLV. Coupled with
ground-based observations, analyses 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 h−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 between 2.4 and 3.9 µg m−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.
Evaluation on Air Purifier’s Performance in Reducing the Concentration of Fine Particulate Matter for Occupants according to its Operation Methods
