Atmospheric heating in the US from saharan dust: Tracking the June 2020 event with surface and satellite observations

Abstract

In June 2020, a record level of Saharan dust was transported across the Atlantic Ocean impacting air quality in the Caribbean Basin and the United States (US). Satellite images showed the transport, while a series of ground-based monitoring stations captured the surface impacts as the Saharan dust was transported to the Caribbean basin and then moved into the Southern (Houston, Texas; WL), Eastern (Bone, North Carolina; APP) and Midwestern (Bondville, Illinois; BND) US. The present study characterizes the Saharan dust event (SDE) using a comprehensive set of satellite observations and in-situ measurements of particulate matter (PM), and aerosol optical properties (AOPs; σscat: scattering coefficient, σabs: absorption coefficient, SAE: scattering Ångström exponent and AAE: absorption Ångström exponent). The Saharan dust intrusion was identified at each site by a marked increase in σscat, and AAE and a simultaneous decrease in SAE. A maximum hourly average PM2.5 concentration and σscat (525 nm) of 97.5 μg m−3 and 190 Mm−1 was observed at WL during the SDE. The maximum hourly average σscat (550 nm) for PM10 size cut of 215 and 66.9 Mm−1 was observed at APP and BND, respectively, during the SDE. The AAE at each site reached above 1.3 with an average value of 1.39 ± 0.35, 3.34 ± 0.56 and 1.65 ± 0.27 at WL, APP, and BND, respectively, during the SDE, whereas the average SAE dropped below 0.5 at WL and APP and below 0.9 at BND. The results demonstrated that the identification of SDE using AOPs depends largely on the location of the measurement, which determines the background characteristics of a site. The results suggest that other intensive AOPs like asymmetry parameter (g) and single scattering albedo Ångström exponent (SSAAE) can also be exploited to characterize SDE. Aerosol radiative forcing (ARF) estimates indicate that the SDE resulted in the heating of the atmosphere (+5.37 to +11.8 W m−2) at the rate of 0.11–0.24 K day−1 at the US sites. This atmospheric heating from transported Saharan dust can alter the regional atmospheric dynamics and is relevant to understand potential changes in regional climate.