Size distribution of bioaerosols from biomass burning emissions: Characteristics of bacterial and fungal communities in submicron (PM1.0) and fine (PM2.5) particles

The North China Plain is the agricultural heartland in China. High PM2.5 levels and elevated chemical pollutants have been observed during crop harvest seasons due to open biomass burning. Biomass burning in the wheat-harvest season may significantly deteriorate the regional air quality. The harmful ingredients in smoke particles also have severe implications for toxicity and health effects. Previous studies have illustrated the potential role of bioaerosols as ice-nuclei and cloud condensation nuclei and highlighted their influence on biochemical cycles and human health effects. In a monthly field observation campaign of biomass burning conducted at the summit of Mount Tai in July 2015, we reported the composition, potential role, size distribution of microorganisms in particulate matters PM1.0, PM2.5, and estimated their contribution to particles. The wide-range particle spectrometer suggested that the predominant particles were distributed in submicron particles (PM1.0), which resulted in a similar community structure for bacteria and fungi in PM1.0 and PM2.5. Among bacteria, the predominant Pseudomonas accounted for 18.06% and 21.29% in PM1.0 and PM2.5, respectively. Alternaria covered up to 69.01% and 72.76% of the fungal community in PM1.0 and PM2.5, respectively. A disparity between bacterial communities was identified by the abundance of rare species, such as Bacilli being higher in PM1.0 (2.4%) than in PM2.5 (1.8%), and Defluviicoccus being higher in PM2.5 (2.5%) than in PM1.0 (0.5%), which may be related to cell size and cell growth patterns. Quantitative PCR revealed that microbial cell numbers in PM2.5 were higher than in PM1.0, and that the bacterial cell number was about an order of magnitude greater than the fungal cell number. However, the mass concentration and contribution of fungi to particulate matter was much higher than that of bacteria, suggesting the underestimated role of fungi in atmospheric aerosols. Airborne microorganisms in alpine areas remained less characterized. The findings presented here illustrated the potentially important impacts on air quality and bioaerosol pollution by biomass burning, which provides an essential reference for understanding the transmission and health effects of bioaerosols.