Explanation S2: Reason of selecting PM10 but not PM2.5 as the airborne particulate indicator The two commonly used indicators to describe the relevance between PM and human health are PM10 and PM2.5. PM10, also called coarse particles, are the particles with a diameter of 10 micrometers or less, and PM2.5, also called fine particles, are the particles with a diameter of 2.5 micrometers or less. Admittedly, compared to PM10, PM2.5 has more harmful effects on human health, probably because of the high risks caused by ultra-fine particles (PM0.1). PM10 is primarily used due to data availability. In addition, numerous studies showed that there is strong correlation between PM10 and PM2.5. When there are only available data for PM10, different coefficients are used to estimate PM2.5 concentrations. For example, in the report of national PM2.5 provided by WHO, national conversion factors (PM2.5/PM10 ratio) were by country, and then used to estimate PM2.5 concentrations from PM10. In a worldwide scale, there are still many countries only providing monitored PM10 parameters, so that quite a lot of values of PM2.5 are originated from original PM10 data. Furthermore, varying by locations, the constitutions of PM2.5 in PM10 are different, which suggests the estimation process of PM2.5 from PM10 is complicated and depends on situations. Furthermore, some case studies proved that the uncertainties of PM2.5 data are inherently larger than that of PM10 data, meaning that PM10 is a more stable indicator. In summary, because of the data availability and certainty, the indicator PM10 is more proper than PM2.5 to be the indicator of air pollution in our research.
Explanation S2: Reason of selecting PM10 but not PM2.5 as the airborne particulate indicator The two commonly used indicators to describe the relevance between PM and human health are PM10 and PM2.5. PM10, also called coarse particles, are the particles with a diameter of 10 micrometers or less, and PM2.5, also called fine particles, are the particles with a diameter of 2.5 micrometers or less. Admittedly, compared to PM10, PM2.5 has more harmful effects on human health, probably because of the high risks caused by ultra-fine particles (PM0.1). PM10 is primarily used due to data availability. In addition, numerous studies showed that there is strong correlation between PM10 and PM2.5. When there are only available data for PM10, different coefficients are used to estimate PM2.5 concentrations. For example, in the report of national PM2.5 provided by WHO, national conversion factors (PM2.5/PM10 ratio) were by country, and then used to estimate PM2.5 concentrations from PM10. In a worldwide scale, there are still many countries only providing monitored PM10 parameters, so that quite a lot of values of PM2.5 are originated from original PM10 data. Furthermore, varying by locations, the constitutions of PM2.5 in PM10 are different, which suggests the estimation process of PM2.5 from PM10 is complicated and depends on situations. Furthermore, some case studies proved that the uncertainties of PM2.5 data are inherently larger than that of PM10 data, meaning that PM10 is a more stable indicator. In summary, because of the data availability and certainty, the indicator PM10 is more proper than PM2.5 to be the indicator of air pollution in our research.
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