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

In this study, a cruise campaign was conducted over China marginal seas to measure concentrations of condensation nuclei (Ncn), cloud condensation nuclei (Nccn) and other pollutants during DOY 110 to DOY 135 of 2018. With exhaustedly excluded self-ship emission signals, the mean values of Nccn during the cruise campaign slightly increased from 3.2 ± 1.1 × 103 cm−3 (mean ± standard) at supersaturation (SS) of 0.2 % to 3.9 ± 1.4 × 103 cm−3 at SS of 1.0 %, and the mean value for Ncn was 8.1 ± 4.4 × 103 cm−3. Data analysis showed that marine traffic emissions apparently yielded a large contribution to the increase of Ncn in daytime, especially in marine atmospheres over their heavily travelled sea zones; however, the fresh sources had no clear contribution to the increase of Nccn. This finding was supported by the quantitative relations between Ncn and Nccn at SS = 0.2–1.0 % against mixing ratios of SO2 in self-ship emission plumes, i.e., 1 ppb increase in SO2 corresponds to 1.4 × 104 cm−3 increase in Ncn, but only 30–170 cm−3 increase in Nccn possibly because of abundant organics in the aerosols. The smooth growth of marine traffic derived particles can be observed, reflecting aerosol aging. The estimated hygroscopicity parameter (κ) values were generally as high as 0.46–0.55 under the dominant onshore winds, suggesting inorganic ammonium aerosols likely acting as the major contributor to Nccn through aerosol aging processes largely decomposed organics. Moreover, the influences of the transported new particles from the continent on Ncn and Nccn in the marine atmosphere were also investigated.