Sources and solubility of aerosol phosphorus at a coastal site in northern China: Coarse versus fine particles and spring versus winter

Atmospheric P is of great importance as it is a major source of phosphorus (P) in open oceans, which can limit the primary productivity of ocean ecosystems and indirectly affect global climate. However, the understanding on the sources of atmospheric P, especially water-soluble P in different particle size and the factors that dominate P solubility is limited. This study characterizes P in fine and coarse particles during winter and spring in Qingdao, a coastal city in North China. The average concentration of total P in fine particles was 23 +/- 15 ng/m3 in winter and 28 +/- 24 ng/m3 in spring, while in coarse particles it was 21 +/- 15 ng/m3 in winter and 15 +/- 12 ng/m3 in spring. In spring, fine particles had notably higher concentrations of total P than coarse particles, while in winter, the difference between the two particle sizes was not pronounced. Regardless of the concentration of total P, the sources of total P varied distinctly between fine and coarse particles in both seasons. The concentration of soluble P is obviously higher in spring than in winter for the fine particles but coarse particles show no significant difference between the two seasons. P solubility is always higher in spring compared to winter regardless of the particle size, which can be due to higher relative humidity. Both soluble P concentrations and P solubility were significantly higher in fine particles compared to coarse particles during winter and spring. A higher contribution of combustion emission and higher acidity can be the reasons for the higher P solubility in fine particles in winter. The findings suggest that a comprehensive evaluation of the ecological impacts of atmospheric phosphorus should consider its sources, aerosol acidity, humidity, and differences among fine and coarse particles.