Direct measurement of the impact of the reactive uptake of ammonia and alkylamines on the CCN activity of ambient aerosol sampled during SOAS 2013

The neutralization of condensed-phase organic acids via reaction with gas-phase ammonia or alkylamines to form ammonium and amminium salts, respectively, has been shown to change the supersaturated hygroscopicity (CCN activity) of laboratory generated organic aerosol (1). Understanding the extent to which CCN activity is perturbed by the reactive uptake of reduced nitrogen gases permits us to assess the sensitivity of current models of hygroscopicity to future changes in the concentration of ammonia and alkylamines. Data presented will focus on the measurement of ambient aerosol CCN activity during the 2013 Southern Oxidant and Aerosol Study (SOAS) campaign at Look Rock, TN, as well as changes in CCN activity following the reactive uptake of gas-phase methylamine, dimethylamine, and ammonia. Ambient CCN measurements are compared with literature values from laboratory studies focusing on SOA formed via isoprene oxidation. Implications for the effect of these multi-phase reactions on the cloud formation properties of ambient aerosols and the comparison of field measurements with laboratory-based studies of model compounds will be discussed. References: 1. Dinar, E. et al., CCN Activity and Hygroscopic growth of organic aerosols following reactive uptake of ammonia, Environ. Sci. Technol., 42, 793-799, 2008.