Variations in Ncn and Nccn over marginal seas in China related to marine traffic emissions, new particle formation and aerosol aging

In this study, a cruise campaign was conducted over marginal seas in China to measure the concentrations of condensation nuclei ( Ncn ), cloud condensation nuclei ( Nccn ) and other pollutants from day of year (DOY) 110 to DOY 135 of 2018. The ship self-emission signals were exhaustively excluded, and the mean values of Nccn during the cruise campaign were found to slightly increase from 3.2 ± 1.1 × 10 3 cm −3 (mean ± standard deviation) at supersaturation (SS) of 0.2 % to 3.9 ± 1.4 × 10 3 cm −3 at SS of 1.0 %, and the mean value for Ncn was 8.1 ± 4.4 × 10 3 cm −3 . Data analysis showed that marine traffic emissions apparently largely contributed to the increase in Ncn in the daytime, especially in the marine atmospheres over heavily traveled sea zones; however, the fresh sources made no clear contribution to the increase in Nccn . This finding was supported by the quantitative relations between Ncn and Nccn at SS = 0.2 %–1.0 % against the mixing ratios of SO2 in the ship self-emission plumes – i.e., a 1 ppb increase in SO2 corresponded to a 1.4×104 cm −3 increase in Ncn but only a 30–170 cm −3 increase in Nccn , possibly because of abundant organics in the aerosols. Smooth growth can be observed in the marine-traffic-derived particles, reflecting aerosol aging. The estimated hygroscopicity parameter ( κ ) values were generally as high as 0.46–0.55 under the dominant onshore winds, suggesting that inorganic ammonium aerosols likely acted as the major contributor to Nccn largely through aerosol aging processes of decomposing organics. Moreover, the influences of the new transported particles from the continent on the Ncn and Nccn in the marine atmosphere were investigated.