Significant influence of urban human activities and marine input on rainwater chemistry in a coastal large city, China.

The coastal urban region is generally considered an atmospheric receptor for terrestrial and marine input materials, and rainfall chemistry can trace the wet scavenging process of these materials. Fast urbanization in China's east coastal areas has greatly altered the rainwater chemistry. However, the chemical variations, determinants, and sources of rainfall are unclear. Therefore, the typical coastal city of Fuzhou was selected for 1-year rainwater sampling and inorganic ions were detected to explore above problems. The findings depicted that rainwater ions in Fuzhou were slightly different from those in other coastal cities. Although NO, SO, Ca and NH dominated the rainwater ions, the marine input Cl (22 %) and Na (11 %) also contributed a considerable percentage to the rainwater ions. Large differences in ion concentrations (2∼28 times) were found in monthly scale due to the rainfall amount. Both natural and anthropogenic determinants influenced the rainwater ions in coastal cities, such as SO emission, air SO and PM content on rainwater SO, NO, and Ca, and soot & dust emission on rainwater SO, NO, indicating the vital contribution of human activities. Stoichiometry and positive matrix factorization-based sources identification indicated that atmospheric dust/particles were the primary contributor of Ca (83.3 %) and F (83.7 %), and considerable contributor of SO (39.5 %), NO (38.3 %) and K (41.5 %). Anthropogenic origins, such as urban waste volatilization and fuel combustion emission, contributed 95 % of NH, 54.5 % of NO and 41.9 % of SO, and the traffic sources contribution was relatively higher than fixed emission sources. The marine input represented the vital source of Cl (77.7 %), Na (84.9 %), and Mg (55.3 %). This work highlights the significant influence of urban human activities and marine input on rainwater chemicals and provides new insight into the material cycle between the atmosphere and earth-surface in coastal city.