[Characteristics and Impact Factors of Number Concentration of Primary Biological Aerosol Particles in Beijing]

Primary biological aerosol particles (PBAP) are an important part of ambient aerosols. Both living and dead organisms not only influence human health and air quality but also play important roles in regulating certain atmospheric processes and affect the hydrological cycle and climate change. In this study, flow cytometry (FCM) was utilized in combination with the simultaneous use of permeant (SYBR Green I) and impermeant (propidium iodide, PI) nucleic acid fluorescent staining to detect and quantify the viable and dead airborne biological particles. At the same time, based on this method, the dead/viable PBAP in a Beijing urban area was detected and quantified. Moreover, the influence of environmental factors on the concentrations of primary biological aerosol particles was illuminated. The results showed that the media number concentration of dead and alive PBAP in the Beijing urban area during summer (1.03×10⁶ m^-3 and 7.43×10⁵ m^-3, respectively) were higher than those during winter (7.34×10⁵ m^-3and 6.18×10⁵ m^-3, respectively). Statistical analysis showed that there was no significant correlation between PBAP number concentration and environmental factors, i.e., meteorological conditions and air quality, showing a weak positive correlation with temperature and humidity and weak negative correlations with O₃, maximum wind speed, and sunshine duration. The number concentration of PBAP was weakly correlated with the mass concentration of PM_2.5 but positively correlated with that of coarse particulate matter (PM_2.5-10). Both stable weather and dust transport could increase the number concentration of PBAP in Beijing.