Index Geophysics

Influence of crustal dust and sea spray supermicron particle concentrations and acidity on inorganic NO3− aerosol during the 2013 Southern Oxidant and Aerosol Study

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.

Allen, H. M.

Draper, D. C.

Ayres, B. R.

Ault, A.

Bondy, A.

Takahama, S.

Modini, R. L.

Baumann, K.

Edgerton, E.

Knote, C.

Laskin, A.

Wang, B.

Fry, J. L.

2018-09-09

Text

application/pdf

10.5194/acp-15-10669-2015

https://acp.copernicus.org/articles/15/10669/2015/

eISSN: 1680-7324

eng