Influence of crustal dust and sea spray supermicron particle concentrations and acidity on inorganic NO<sub>3</sub><sup>−</sup> aerosol during the 2013 Southern Oxidant and Aerosol Study

Abstract

Abstract. Inorganic aerosol composition was measured in the southeastern United States, a region that exhibits high aerosol mass loading during the summer, as part of the 2013 Southern Oxidant and Aerosol Study (SOAS) campaign. Measurements using a Monitor for AeRosols and GAses (MARGA) revealed two periods of high aerosol nitrate (NO3−) concentrations during the campaign. These periods of high nitrate were correlated with increased concentrations of supermicron crustal and sea spray aerosol species, particularly Na+ and Ca2+, and with a shift towards aerosol with larger (1 to 2.5 μm) diameters. We suggest this nitrate aerosol forms by multiphase reactions of HNO3 and particles, reactions that are facilitated by transport of crustal dust and sea spray aerosol from a source within the United States. The observed high aerosol acidity prevents the formation of NH4NO3, the inorganic nitrogen species often dominant in fine-mode aerosol at higher pH. Calculation of the rate of the heterogeneous uptake of HNO3 on mineral aerosol supports the conclusion that aerosol NO3− is produced primarily by this process, and is likely limited by the availability of mineral cation-containing aerosol surface area. Modeling of NO3− and HNO3 by thermodynamic equilibrium models (ISORROPIA II and E-AIM) reveals the importance of including mineral cations in the southeastern United States to accurately balance ion species and predict gas–aerosol phase partitioning.

The underappreciated role of nonvolatile cations on aerosol ammonium-sulfate molar ratios

“…1 period, predicted R was on average 1.43 ± 0.32 for an ISORROPIA input with inferred Na + , 1.85 ± 0.17 for measured Na + input, and the highest R at 1.97 ± 0.02 when zero Na + was used as model input. The average measured R was 1.70 ± 0.23 by PILS-IC and 1.75 ± 0.20 by another PM2.5 water-soluble ion measurement (Allen et al, 2015). Thus, model R with measure Na + input was closest to the measured R. Under the meteorological conditions of the southeast in summertime (T = 25 ± 5 °C, RH = 68 ± 18 %), the thermodynamic model predicts R always near or equal to 40…”

Photochemical organonitrate formation in wet aerosols

“…ALW in turn facilitates aerosol partitioning of HNO 3 . Field observations support HNO 3 uptake by aerosol waters during the daytime (Allen et al, 2015;Hodas et al, 2014). Notably, nitrate concentrations are strongly correlated with water-soluble organic compound concentrations (Hennigan et al, 2008b).…”

The sensitivity of PM<sub>2.5</sub> acidity to meteorological parameters and chemical composition changes: 10-year records from six Canadian monitoring sites

“…The details of these monitoring sites including their longitudes and latitudes, NAPS monitoring station codes, and duration of the data record used for this study can be found in Table S1 in the Supplement. These sites were chosen because (1) they have long-term (at least 8-year) records of gaseous and PM 2.5 chemical components concentrations, and (2) they are located in the central region of North America with little influence of sea salt (Vet et al, 2014) and therefore the acidity of PM 2.5 is mainly dominated by the chemistry of sulfate, total nitrate and total ammonia (Young et al, 2013;Allen et al, 2015;Hennigan et al, 2015).…”