Transport of bacterial cells toward the Pacific in Northern Hemisphere westerly winds

Viable and non-viable bacteria in the air were investigated on the southwestern Japan coast to outline the manner by which bacteria were transported and to quantify the bacterial abundance and viability in the Northern Hemisphere westerly winds. The observations were conducted when the weather was governed by cyclones or anticyclones associated with Asian continent outflow between 12 October 2011 and 7 April 2013. Bacterial concentration in thermodynamically different air parcels was in the same order but different ranges: 4.5 × 105-1.3 × 106 cells m−3 in postfrontal air, 2.4 × 105-1.4 × 106 cells m−3 in prefrontal air, 5.4 × 105-9.9 × 105 cells m−3 in the air between cyclones and anticyclones and 2.9 × 105-4.1 × 105 cells m−3 in anticyclone air. In postfrontal air, the concentration correlated closely with coarse aerosol particles (diameter > 1.0 μm). In contrast, bacteria did not show a correlation with coarse particles in prefrontal air and anticyclone air. Bacterial viability was approximately 70% on average of all samples. However, the viability in postfrontal air was smaller than 60% if cases of stationary fronts with stagnant air were excluded. These results indicate that air parcels following fast-moving cold fronts in the westerly wind flow constantly and efficiently conveyed airborne bacteria from the Asian continent toward northwestern Pacific and the bacteria were characterized by coarse particle-correlated high abundance and low viability. The bacteria in slowly moving anticyclone and prefrontal air, characterized by low abundance and high viability, were more likely a mixture of long-range transported ones and regionally or locally originated ones.