Concentration of bacterial aerosols in response to synoptic weather and land‐sea breeze at a seaside site downwind of the Asian continent

Abstract

AbstractAirborne bacteria are a major group of bioaerosols, but their temporal and spatial variations in the atmosphere are poorly understood due to a lack of accurate information at an appropriate temporal resolution. In this study, we quantified the concentration and viability of airborne bacteria at a seaside site on the southwestern coast of Japan in spring to investigate their association with synoptic weather, which was governed alternately by cyclones and anticyclones moving in the middle‐latitude westerly flow. The concentration of bacteria, on the order of 105–106 cells m−3, showed a small amplitude of variation, while the viability significantly differed in the range of 23–96% under different weather conditions. Cyclones transported bacteria from the Asian continent in their postfrontal air. Compared to bacteria under other weather conditions, the bacteria in postfrontal air had a large concentration, a low viability, and a close correlation with coarse aerosol particles. In contrast, bacterial concentration and viability in prefrontal air varied over small ranges, and no correlation between bacteria and aerosol particle number concentration was observed. During anticyclones, although bacterial concentration was similar to that in prefrontal air, bacterial viability was high, and the concentration had pulse increases of approximately 2 times the usual level when the wind changed to land/sea breezes. The increases were attributed to the accumulation of bacteria in stagnant air due to local sources. These results show the following two distinct patterns of bacterial concentration and viability at the seaside location of this study: (1) during postfrontal long‐distance dust plume transport related to a cyclone approaching from the Asian continent, the bacterial concentration is correlated with the coarse aerosol particle number concentration and the bacterial viability is low, and (2) pulse increases of viable bacteria are observed at anticyclone conditions corresponding to local sources and land‐sea breeze conditions.