Characterization Of Fluorescent Bioaerosols In Tianjin During Summer And Winter

Bioaerosols are an important subset of atmospheric aerosols.Bioaerosols play an important role in weather,climate,human health,crop and livestock health,as well as ecosystems.Due to the complex and diverse composition of bioaerosols,the emission and diffusion mechanisms remain unclear.Bioaerosols are greatly affected by the changes of regional environment.The research is still quite inadequate on the impacts of bioaerosols on global changes,public health and ecosystems.Exploring the abundance and emission characteristics of bioaerosols not only helps to understand the contribution of bioaerosols to global organic aerosols,but also helps to gain a deeper understanding of the global cycle of biological particles.Tianjin is the largest coastal city in North China,which is adjacent to Beijing and the Bohai Sea.It is affected by both anthropogenic activities and marine air masses.In summer,Tianjin is affected by the air masses from both continental and marine areas,and it rains frequently.The main pollutants are from both local emissions and longdistance transportation.In winter,the air masses mainly come from the northwest.The contributions of fossil fuel combustion and biomass burning increase,and due to the frequent occurrences of stable weather,the frequency of haze conditions increase in which terrestrial pollution sources are significant.In this study,a Wideband Integrated Bioaerosol Sensor(WIBS)was used to perform real-time field observations of fluorescent bioaerosols during summer and winter in Tianjin urban area.Filter-based aerosol samples were analyzed for watersoluble ions and organic carbons.Combining with air quality parameters,meteorological parameters,and the backward trajectories of air masses,fluorescent bioaerosols in Tianjin were investigated for their variations in number concentrations,particle size distributions and possible emission mechanisms.The main conclusions of this study are as follows:(1)The daily circle of bioaerosols was greatly affected by relative humidity(RH).In summer,the abundance of bioaerosols peaked at sunrise(～7:00)and reached the lowest value around 2:00 p.m.During winter clean periods,the highest concentration of bioaerosols appeared at midnight.During the polluted periods,the bioaerosol concentration peaked at around 9:00 a.m.with broader changes,which may be more significantly affected by human activities.(2)The number concentration of fluorescent aerosol particles in winter was higher than that in summer.This may be caused by the frequent occurrence of static and stable weather conditions in winter and the decrease in the height of the atmospheric boundary layer,which inhibited the dispersal of particles.In addition,the increase in biomass burning and fossil fuel combustion in winter could increase the atmospheric concentrations of bioaerosols and certain nonbiological fluorescent interferences.(3)In the summer,due to the emission of biological sources such as fungal spores and pollen fragments,the contribution of coarse particles to bioaerosols was significant.In winter,fluorescent aerosols were mainly contributed by fine mode particles(～1 μm)with a higher contribution fraction during the polluted periods.(4)The contribution of marine air masses to the concentrations of bioaerosol particles in Tianjin urban area was minor.Bioaerosols in urban Tianjin may mainly came from land-surface emissions.The regional transport from the south of Tianjin contributed significantly to the increase in the number concentration of fluorescent particles in the winter polluted periods.Besides,the concentration of biological aerosols in the air masses sinking from high altitudes was less than those moving along the land surface.(5)The precipitation process would promote the emission of fungal spores,bacteria and other biological particles into the atmosphere.The emission rate was greater than the scavenging rate of atmospheric particles by raindrops.In summer,the ambient temperature contributed significantly to the increase in the concentration of bioaerosol particles,and changes in wind speed had little effect.On the contrary,in winter,air temperature contributed less to changes in bioaerosol particles.At low wind speeds,the concentration of particles increased due to accumulation effect.