Analysis Of Microbial Aerosol Contamination In Commuter Motor Vehicles And Underpasses And Its Correlation With Particulate Matter

Microbial aerosol concentration is one of the important reference indicators for evaluating indoor air quality,which directly affects people’s health.At present,related studies at home and abroad mainly focus on the study of air microbial aerosol pollution characteristics in indoor public buildings,but lack research on air microbial pollution characteristics in commuter motor vehicles and commuter underpasses.Since the microbial exposure of the population in the commuter environment is also an important part of the total daily pollutant exposure of urban residents,the air quality of the commuter environment can have an impact on human health.Therefore,the study of microbial aerosol pollution characteristics,exposure levels and the effect of ventilation conditions on microbial concentration levels in commuter motor vehicles and pedestrian underpasses is an important reference for improving microbial aerosol pollution in commuter environments and reducing the risk to human health from microbial exposure,and can provide important basic data for the development of relevant health standards in commuter environments.In view of this,this paper selected passenger cars,buses and pedestrian underpasses as the study subjects and used the impact method to sample the microorganisms in the air inside the study subjects and monitored PM_1.0,PM_2.5 and PM₁₀ in the study environment,while recording the flow of people and ventilation conditions during the sampling period.The data were processed and analysed to investigate the levels of microbial contamination in the air inside commuter motor vehicles and underpasses,the percentage of microbial aerosols in the total concentration in different particle size bands and the correlation between microbial aerosols and particulate matters.The impact of airborne microbial exposure in commuter motor vehicles on human health was also assessed,the effect of airflow patterns and ambient wind speed on the distribution of microbial aerosol concentrations in commuter motor vehicle compartments was analysed using a dispersion model,with the following main findings:（1）Overall bacterial and fungal aerosol concentration levels in commuter motor vehicle compartments and underpasses:evening peak>morning peak,with microbial aerosol concentration levels in commuter motor vehicles:bus>minibus,passenger seat>driver seat.Air quality is cleaner inside passenger car and fungal contamination is more severe inside buses and underpasses.And the concentration of bacterial and fungal aerosols within the commuter environment was significantly and positively correlated with the flow of people.（2）The particle size of fungal aerosols in commuter motor vehicle compartments and underpasses was mainly distributed in Class III to V（1.1～4.7μm）.The particle size of bacterial aerosols in the commuter compartment was mainly distributed in Class II to IV（2.1～7.0μm）,while there were differences between the morning and evening peak hours in the underpass,with the particle size of bacterial aerosols mainly distributed in Class I to III（>3.3μm）during the morning peak and in Class IV to VI（0.65～3.3μm）during the evening peak.（3）Total bacterial and fungal concentrations in commuter motor vehicle compartments and underpasses were positively correlated with PM_1.0,PM_2.5 and PM₁₀,and the strongest correlations were found between PM_1.0,PM_2.5 and PM₁₀ and bacterial aerosols with particle size distribution in class VI within the environment.PM_2.5 and PM₁₀ in passenger cars and buses were all significantly and positively correlated with fungal aerosols with particle size distribution in Class IV to V,while PM_2.5 and PM₁₀ in underpasses were all significantly and positively correlated with fungal aerosols with particle size distribution in Class V to VI.Furthermore,the comparative analysis revealed that PM_1.0 and PM_2.5 adsorbed more microbial components on the same mass of particulate matter in the commuter compartments and the underpasses,which may be more harmful to human health and need more attention.（4）The health impact coefficients for microbial exposure in commuter motor vehicle compartments are all less than 1,indicating that microbial aerosol exposure in commuter vehicle compartments has a low impact on human health.However,the health impacts on men were higher than women and the health impact on drivers were higher than passengers,while the overall health impacts on people inside buses were known to be higher than those inside passenger car.（5）The diffusion model shows that the side airflow form is better than the top airflow in controlling microbial contamination in the cabin,and that increasing the airflow speed in the cabin can effectively reduce the concentration of microbial aerosols while satisfying the comfort of the personnel.