Nowcasting Applications of Geostationary Satellite Hourly Surface PM2.5 Data

Abstract

Abstract The mass concentration of fine particulate matter (PM 2.5 ; diameters less than 2.5 μ m) estimated from geostationary satellite aerosol optical depth (AOD) data can supplement the network of ground monitors with high temporal (hourly) resolution. Estimates of PM 2.5 over the United States were derived from NOAA’s operational geostationary satellites’ Advanced Baseline Imager (ABI) AOD data using a geographically weighted regression with hourly and daily temporal resolution. Validation versus ground observations shows a mean bias of −21.4% and −15.3% for hourly and daily PM 2.5 estimates, respectively, for concentrations ranging from 0 to 1000 μ g m −3 . Because satellites only observe AOD in the daytime, the relation between observed daytime PM 2.5 and daily mean PM 2.5 was evaluated using ground measurements; PM 2.5 estimated from ABI AODs were also examined to study this relationship. The ground measurements show that daytime mean PM 2.5 has good correlation ( r > 0.8) with daily mean PM 2.5 in most areas of the United States, but with pronounced differences in the western United States due to temporal variations caused by wildfire smoke; the relation between the daytime and daily PM 2.5 estimated from the ABI AODs has a similar pattern. While daily or daytime estimated PM 2.5 provides exposure information in the context of the PM 2.5 standard (>35 μ g m −3 ), the hourly estimates of PM 2.5 used in nowcasting show promise for alerts and warnings of harmful air quality. The geostationary satellite based PM 2.5 estimates inform the public of harmful air quality 10 times more than standard ground observations (1.8 versus 0.17 million people per hour). Significance Statement Fine particulate matter (PM 2.5 ; diameters less than 2.5 μ m) are generated from smoke, dust, and emissions from industrial, transportation, and other sectors. They are harmful to human health and even lead to premature mortality. Data from geostationary satellites can help estimate surface PM 2.5 exposure by filling in gaps that are not covered by ground monitors. With this information, people can plan their outdoor activities accordingly. This study shows that availability of hourly PM 2.5 observations covering the entire continental United States is more informative to the public about harmful exposure to pollution. On average, 1.8 million people per hour can be informed using satellite data compared to 0.17 million people per hour based on ground observations alone.