Bioaerosol Concentrations and Size Distributions during the Autumn and Winter Seasons in an Industrial City of Central China

The ambient bioaerosols were measured in PM_2.5 and PM₁₀ samples taken in Huangshi City, Hubei Province, China, during autumn and winter from November 2017 to February 2018. Both the bioaerosol number concentration and size distribution (0.37-16 μm) were obtained by direct fluorescent staining coupled with microscopic imaging. The bioaerosol number concentrations ranged from 0.05 to 3.4 # cm^-3 for PM_2.5 and from 0.17 to 5.7 # cm^-3 for PM₁₀, with averages of 0.90 # cm^-3 and 1.9 # cm^-3, respectively. In terms of particle number, the bioaerosols were dominated by fine particles (0.37-2.5 μm in diameter), with a larger proportion of submicron than supermicron particles. Assuming a unit density of 1 g cm^-3 and a spherical shape for the particles, the mass abundances of the bioaerosols were estimated to be 2.4 ± 1.9% and 4.8 ± 3.2% of the PM_2.5 and PM₁₀, respectively, as measured by a nearby compliance monitor. Higher bioaerosol concentrations were observed in winter than autumn and on polluted than non-polluted days. During heavily polluted conditions, bioaerosols in the PM_2.5 and PM₁₀ were enriched by 6 and 3.7 times, respectively, compared to non-polluted days and contributed up to 15% of the PM₁₀ mass. Rainfall and snowfall appeared to lower the bioaerosol levels. As enhanced emission controls on combustion and dust sources decrease PM levels in China, the bioaerosol fraction in measured PM concentrations will likely increase.