Hygroscopic behavior of water-soluble matter in marine aerosols over the East China Sea

摘要

In this study, we investigated hygroscopic properties of water-soluble matter (WSM) in marine aerosols over the East China Sea, which were collected during a Natural Science Foundation of China (NSFC) sharing cruise in 2014. Hygroscopic growth factors (g) of WSM were measured by a hygroscopicity tandem differential mobility analyzer (H-TDMA) with an initial dry particle mobility diameter of 100 nm. The observed g at 90% relative humidity (RH), g(90%)_(WSM). defined as the ratio of the particle diameter at 90% RH to that at RH ＜ 5% (initial dry diameter), ranged from 1.67 to 2.41 (mean ± std: 1.99 ± 0.23).The g values were lower than that of seawater (2.1) but comparable with those reported for marine aerosols (1.79-2.08). The H-TDMA retrieved hygroscopicity parameter of WSM, k_(WSM). ranged from 0.46 to 1.56 (0.88 ± 0.35). The observed g(90%)_(WSM) during the daytime ranged from 1.67 to 2.40 (1.95 ± 0.21) versus 1.71 to 2.41 (2.03 ± 0.26) during the nighttime. k_(WSM) was 0.81 ± 0.32 in the daytime and 0.95 ± 0.40 in the nighttime. The dayight differences of g(90%)_(WSM) and k_(WSM) indicated that nighttime marine aerosols were more hygroscopic than those in daytime, which was likely related to enhanced heterogeneous reaction of ammonium nitrate in nighttime and the higher Cl~-/Na~+ molar ratios obtained (0.80) in nighttime than those (0.47) in daytime. Inorganic ions accounted for 72-99% of WSM with SO_4~(2-) being the dominant species, contributing to 47% of the total inorganic ion mass. The declined g(90%) comparing with sea water was likely due to the transport of anthropogenic aerosols, chemical aging of dust particles, the contribution of biomass burning products, and the aerosol hygroscopic growth inhibition of organics.