Characteristics and Influencing Factors of the Microbial Concentration and Activity in Atmospheric Aerosols over the South China Sea

Oceans are important sources of microbes in atmospheric aerosols; however, information about the characteristics of airborne microbes and their influencing factors over oceans is lacking. Here we report the characteristics of the microbial abundance and activity in aerosols sampled near the sea surface over the South China Sea (SCS) from May to June 2016. The airborne microbial concentration range in the aerosols was 1.68×10 5 to 4.84×10 5 cells m −3 over the SCS, reflecting an average decrease of 40%–54% over the SCS compared with that in the samples from the coastal region of Qingdao. About 63%–76% of the airborne microbes occurred in coarse particles (> 2.1 µm), with a variable size distribution over the SCS. The microbial activity range in aerosols, measured by the fluorescein diacetate (FDA) hydrolysis method, was 2.09–11.97 ng m −3 h −1 sodium fluorescein (SF) over the SCS, which was 15%–79% lower than that over the coastal region. These values reflected a different spatial distribution over the SCS from that of the microbial concentration. Except for certain samples, all samples had 68% of the microbial activity occurring in coarse particles. Correlation analysis showed that the microbial abundance and activity were positively correlated with the aerosol, organic carbon (OC), and water-soluble organic carbon (WSOC) concentrations, indicating that the airborne microbes may be related to the reactions of certain water-soluble organic chemicals in the atmosphere. Moreover, the concentrations of airborne microbes were significantly negatively correlated with the horizontal offshore distance. The microbial concentration and activity were significantly correlated with wind speed.