Diurnal variation of smoke height retrieved from EPIC/DSCOVR: Implications for estimating surface PM2.5 pollution and atmospheric vertical motion vector

A series of huge smoke plume events from the largest wildfire season recorded in California's modern history have occurred in 2020. Here, a research algorithm was applied to determine the optical centroid height (AOCH) and optical depth (AOD) for smoke aerosols over vegetated land from the Earth Polychromatic Imaging Camera (EPIC) measurements of several severe fire events in September 2020 in the Western U.S. This study has provided insights of the algorithm feasibility under heavy smoke conditions and for studying the diurnal variation of smoke layer height; the latter is only possible via EPIC due to its unique orbital position at the Earth-Sun Lagrange-1 point and its equipment of the O2B-band at which the vegetated surface reflectance is low. Results show that the large smoke plumes in Western U.S. on Sep. 6-7 and the smoke layers transported to the Eastern U.S. on Sep. 14-16 were injected into the free troposphere at 2-10 km in most areas. The EPIC AOCH retrievals are around 2 km higher than the TROPOMI operational aerosol layer height products on average but agree well with CALIOP extinction weighted height with a correlation coefficient (R) of 0.886 and root mean square error (RMSE) of 0.91 km for the smokes on Sep. 14-16. Distinct diurnal variation of AOCH is also found, for example, on Sep. 7, from 6.0 km in the local morning to 4.3 km at noon time, with a mean smoke vertical velocity of around -0.13 m s-1. The descending of smoke layer leads to the increase of surface PM2.5 pollution, which can be quantitatively explained by a simple box model. Finally, ~62% of data values of smoke layer vertical motion vector derived from the consecutive hours of AOCH has the same direction as that of the atmospheric vertical velocity from MERRA-2, although there is some discrepancy in their magnitude. This work shows the high potential of future geostationary satellites that carry the O2 B-band, such as TEMPO and GEO-XO, for improving surface air quality monitoring and air quality forecast.