Particle Size Distribution And Human Deposition Characteristics Of Bioaerosols In Xi’an

The outbreak and spread of infectious diseases such as SARS-Co V-2 and H1N1 have made bioaerosol a hot topic of environment.Bioaerosols carring bacteria,fungi,viruses and other microorganisms transmit and diffuse in the indoor and outdoor air environment.Aerosol with small particle size can enter the human body through respiration,which may cause allergies,respiratory system and even systemic diseases,resulting in potential health risks.At present,most studies on the health effects of bioaerosols are based on environmental concentration,ignoring the real dose of bioaerosols in human body.Therefore,in order to quantitatively explore the deposition characteristics of bioaerosols in human respiratory system,this paper selected Xi’an urban area as sampling point,collected atmospheric particulate matter samples of different particle sizes and culturable bioaerosol samples（bacteria and fungi）from May 2022 to February 2023,analyzed the total airborne microorganisms and protein in the particulate matter,and explored the concentration level and particle size distribution characteristics of different types of bioaerosol.Multiple path particle dosimetry models（MPPD）was used to calculate the deposition fraction and deposition dose of bioaerosol in different populations and different parts of respiratory system,providing scientific basis for health risk assessment.The main conclusions are as follows:（1）The average annual concentration of total microorganisms on PM₁₀and PM_2.1in Xi’an was（20.84±10.89）×10⁴cells/m³and（8.16±4.19）×10⁴cells/m³,respectively.The monthly average concentration was the highest in December and the lowest in July,and the seasonal variation was winter>autumn>spring>summer.The particle size with the highest average annual concentration ranges from 4.7 to 5.8μm,and the particle size distribution function is bimodal,which is consistent with the particle size distribution of the mass concentration.The total microbial concentration of different particle sizes was negatively correlated with temperature and solar radiation（p<0.05）.The three particle size segments of<0.43μm,1.1～2.1μm and 5.8～9μm were significantly affected by temperature.（2）The average annual concentration of culturable bacterial aerosol in Xi’an was832±536 CFU/m³,and the highest concentration was in the range of 3.3～4.7μm.The highest monthly concentration appeared in November and the lowest in May,and the seasonal variation was autumn>winter>summer>spring.The average annual concentration of culturable fungal aerosol was 372±197 CFU/m³,which was significantly lower than that of bacterial aerosol（p<0.05）;The concentration of 7μm was the highest,the monthly average concentration was the highest in December and the lowest in June,and the seasonal variation was winter>spring>autumn>summer.The concentration and particle size distribution of culturable bioaerosol were different in different months and seasons.（3）The average annual concentrations of protein components in PM₁₀and PM_2.1in Xi’an were 3.42±1.42μg/m³and 1.40±0.58μg/m³,respectively,accounting for 1.4～5.2%of the mass concentration of particulate matter.The monthly average concentration was the highest in December and the lowest in June and July,and the seasonal variation was winter>autumn>spring>summer.The three particle size segments with the highest annual protein concentration were 9～10μm,5.8～9μm and 4.7～5.8μm,all distributed in the coarse particle size segment.The particle size distribution function was bimodal,with the main peak in the range of 4.7～5.8μm,which was the same as the particle size distribution function of total microbial concentration in the air.（4）The deposition amount of bioaerosol is the largest outside the human chest,and the deposition dose in the tracheobronchus is the smallest.The total deposition dose in men is greater than that in women,and the deposition dose in children and the elderly is higher.The deposition dose of different types of bioaerosols in human body has a certain seasonal rule and is at a higher level in autumn and winter.The concentrations of total airborne microorganisms in different populations ranged from 5.95×10⁴to 10.85×10⁴cells/h,the culturable bacterial aerosols ranged from 268 to 470 CFU/h,and the culturable fungal aerosols ranged from 123 to 213 CFU/h.The proteome was 0.937 to 1.73μg/h.