Children’s Exposure To Particulate Matter While Commuting To School

Particulate matter on both sides of the city road shows the"double high"characteristics of high emission rate and high pollution concentration.Children are more severely affected by traffic-related pollutants due to their more active state and immature defense system,and long-term exposure to high pollution levels not only affects their cardiovascular or respiratory systems,but also leads to poorer performance in intelligence and memory assessment.Therefore,it is important to conduct studies on the analysis of exposure and health effects of different modes in children to improve traffic emissions and safeguard children’s health.In this paper,we selected a typical home-to-school commuting route in Xi’an and conducted pollutant monitoring experiments using mobile devices on the three most used commuting modes（walking,private cars and electric bicycles）by Chinese children to investigate the exposure characteristics of black carbon（BC）and particulate matter（PM）to which children were exposed during their daily commuting to school.Correlation analysis and multiple linear regression analysis were used to reveal the effects of meteorology,traffic volume,time of day and urban background concentrations.A multiparameter respiration rate assessment model was used to compare the differences in inhaled doses of pollutants between different modes,and a multipath particle dosimetry model（MPPD）was used to quantify the fractions of particles deposited in different parts of the respiratory system of children and the deposited doses.The main findings are as follows:First,the mode of commuting influenced pollutant exposure levels and spatial and temporal characteristics.The lowest PM₁,PM_2.5 and BC exposure concentrations were found under walking,but the highest average PM₁₀ concentrations were reached,while private cars and e-bikes put children at high PM and BC exposures,especially PM₁ and BC concentrations reached the highest during e-bike trips.Walking and e-bike modes were easily influenced by the surrounding environment making pollutant concentrations appeared elevated in the short term,with private cars showing higher peaks when windows were open and less change in pollutants inside the car when windows were closed.In addition,dense commercial areas,intersections and bus stops were hotspots for children’s exposure to air pollution.Second,the results of the influence factor analysis showed that（1）there was a significant correlation between PM(PM₁,PM_2.5 and PM₁₀),but no significant correlation between PM and BC in private car and e-bike commuting,indicating other sources of BC emissions.（2）Urban background concentration levels were the most important determinants of PM_2.5（explaining 75.4%-91.9%of the variation）and PM₁₀（explaining 77.9%-93.3%of the variation）concentrations.Wind speed was an important factor for BC exposure in private car and e-bike commuting,but had no significant effect in walking.Time of day（morning and evening）was also an important determinant of private car BC and e-bike PM₁₀ exposure.Finally,the health effects of pollutants were assessed by inhaled dose,deposition fraction and deposition dose.The particle size determined the deposition site:the highest deposition fraction and deposition dose（over 50%）were found in the head,and the deposition dose of fine particles(BC,PM₁ and PM_2.5)was higher in the alveolar region than in the bronchial region,but the deposition fraction of coarse particles(PM₁₀)was very small in the alveolar region.Active commuting mode（walking）inhaled and deposited higher doses of pollutants than passive commuting mode（private car,e-bike）.Men deposited 10%-20%higher doses than females.