RH showed the highest values at the Huaniao Isle among the three sites, ranging from 69% to 86% during the study period and averaged (80 ± 14)% in PD_HN. The correlation between NH4 and ð½NO3 2½SO4 as a function of RH was as similar as Shanghai while differed a lot from Beijing (Fig. 5c). During ND_HN, the ratio of ð½NO3 2½SO4 2Þ=½NH4 was close to 1.0, indicating that sulfate and nitrate were almost fully neutralized by ammonium in the normal days at this isle. While during PD_HN, this ratio slightly increased to 1.3, indicating that the marine aerosol over this isle was weakly acidic and it was evidently from the regional/longrange transport of the anthropogenic emissions in the mainland
of China.