To exclude the contribution from marine source to SO4 in the aerosols over the Huaniao Isle, nss SO4 could be estimated based on the assumption that all Naþ was from the marine source using the marine SO4/Na+ ratio of 0.25. It was calculated that nss SO4 accounted for 99% of the total SO4 during both ND_HN and PD_HN, indicating that SO4 of the Huaniao Isle was dominantly contributed by anthropogenic sources.