Connect column aerosol optical depth (AOD) with surface PM2.5 concentration and extinction

Remotely sensed column aerosol optical depth (AOD) is often used to derive the aerosol mass concentration (e.g. PM2.5) and aerosol types (i.e. chemical composition) near the earth surface, which are critical to air quality monitoring and research. We collected the measurements of aerosol mass concentration, optical properties, and relevant meteorological conditions from two NASA field missions: DISCOVER-AQ and KORUS-AQ. In most places, including stations in both North America and East Asia, surface aerosol extinction and mass concentration are highly correlated while the relationship is quite different among stations. We then used surface aerosol extinction as a bridge to connect the surface PM2.5 and column AOD. AOD is affected by many factors other than the dry aerosol concentration, e.g. the seasonal variation of AOD is also driven by the humidity change, and the diurnal cycle of AOD and PM2.5 are affected by planetary boundary layer height differently.