Spatiotemporal Changes in PM 2.5 and Their Relationships with Land-Use and People in Hangzhou.

Increases in the extent and level of air pollution in Chinese cities have become a major concern of the public and burden on the government. While ample literature has focused on the status, changes and causes of air pollution (particularly on PM _2.5 and PM ₁₀ ), significantly less is known on their effects on people. In this study we used Hangzhou, China, as our testbed to assess the direct impact of PM _2.5 on youth populations that are more vulnerable to pollution. We used the ground monitoring data of air quality and Aerosol optical thickness (AOT) product from the Moderate Resolution Imaging Spectroradiometer (MODIS) for the spatiotemporal changes of PM _2.5 by season in 2015. We further explored these distributions with land cover, population density and schools (kindergarten, primary school and middle school) to explore the potential impacts in seeking potential mitigation solutions. We found that the seasonal variation of PM _2.5 concentration was winter > spring > autumn > summer. In Hangzhou, the percentage of land area exposed to PM _2.5 > 50 µg m ^-3 accounted for 59.86% in winter, 56.62% in spring, 40.44% in autumn and 0% in summer, whereas these figures for PM _2.5 of <35 µg m ^-3 were 70.01%, 5.28%, 5.17%, 4.16% in summer, winter, autumn and spring, respectively. As for land cover, forest experienced PM _2.5 of 35⁻50 µg m ^-3 (i.e., lower than those of other cover types), likely due to the potential filtering and absorption function of the forests. More importantly, a quantitative index based on population-weighted exposure level ( pwel ) indicated that only 9.06% of the population lived in areas that met the national air quality standards. Only 1.66% (14,055) of infants and juveniles lived in areas with PM _2.5 of <35 µg m ^-3 . Considering the legacy effects of PM _2.5 over the long-term, we highly recommend improving the monitoring systems for both air quality and people (i.e., their health conditions), with special attention paid to infants and juveniles.