Nowcasting Applications of Geostationary Satellite Hourly Surface PM 2.5 Data.

The mass concentration of fine particulate matter (PM _2.5 ; diameters less than 2.5 μm) 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 (US) 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 μg/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 US, but with pronounced differences in the western US 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 μg/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 ten times more than standard ground observations (1.8 vs. 0.17 million people per hour).