Characteristics and mixing state of amine-containing particles at a rural site in the Pearl River Delta, China

Particulate amines play an important role for the particle acidity and hygroscopicity and also contribute to secondary organic aerosol mass. We investigated the sources and mixing states of particulate amines using a single-particle aerosol mass spectrometer (SPAMS) during summer and winter 2014 at a rural site in the Pearl River Delta, China. Amine-containing particles accounted for 12.8 % and 9.2 % of the total detected individual particles in summer and winter, respectively. Amine-containing particles were classified into three types: elemental and organic carbon (ECOC), biomass burning (BB), and nitrate-rich. ECOC amine-containing particles were the most abundant, constituting 67.2 % and 74.8 % of amine particles in summer and winter, respectively. Both ECOC and BB type amine-containing particles contained abundant carbonaceous and carbon-nitrogen species, as well as sulfate and nitrate, in summer and winter. The nitrate-rich amine-containing particles were mixed with abundant sea-salt markers in summer, indicating a possible association between the amine emission source and marine phytoplankton. In summer, only 6.7 % of the total amine-containing particles were found to be mixed with ammonium, while in winter this percentage increased to 55 %. The ammonium-poor state of amine-containing particles in summer may have been caused by the displacement of particle-phase ammonium by amine uptake, which was more efficient in summer at higher ambient RH (72 ± 13 %) than in winter (63 ±11 %). In ECOC-type amine-containing particles, the time series of the amine peak area and the sum of the nitrate and sulfate peak areas were similar in both summer and winter, suggesting the formation of aminium sulfate and nitrate salts. The particle acidity of ECOC-type amine-containing particles was represented by the relative acidity ratio (R a ), which was defined as the ratio of the total sulfate and nitrate peak areas to the ammonium peak area. The R a decreased from 348 ± 335 and 28 ± 14 to 10 ± 5 and 9 ± 2 in summer and winter, respectively, after including amines along with the ammonium in the acidity calculation, suggesting that it is reasonable to consider amines when estimating particle acidity. Based on the influence of amines on particulate ammonium and particle acidity, particulate amines could have an impact on the newly found missing source of sulfate produced from the oxidation of SO 2 by NO 2 with NH 3 neutralization during haze episodes under high ambient relative humidity in northern China.