Transport and Impacts of the June 2020 Saharan Dust Event on the Continental US

Abstract:

In June 2020, dust originating in the Sahara was transported across the Atlantic impacting air quality and visibility in the continental United States, starting in Texas and moving into the Midwest and Appalachia. Though Saharan dust has annual impacts in the Caribbean and Texas, the June 2020 event was particularly impactful. Satellite images revealed the initial transport, while a series of ground-based monitoring stations captured the surface impacts as the dust storm made landfall in Puerto Rico and then moved on to Texas, Illinois, and North Carolina. With a similar set of instrumentation, these sites offer a real-time assessment of the aerosol optical properties as this massive dust plume is transported across the US. The Puerto Rico, Illinois and North Carolina sites are part of NOAA’s Federated Aerosol Network (NFAN) which monitors aerosol concentration, absorption, scattering and cloud condensation nuclei using a unified protocol and set of instrumentation. The Texas sites are part of the newly constructed Texas Commission on Environmental Quality Black and Brown Carbon (BC)² network which operates in Houston and El Paso using a similar protocol as NFAN to measure aerosol scattering and absorption. The NFAN and (BC)² networks utilize three wavelength aerosol photometers to monitor aerosol absorption and three wavelength nephelometers to monitor aerosol scattering. As the Saharan dust was transported into and through each site, aerosol concentrations increased dramatically with the scattering coefficients while the scattering Ångström exponent decreased to zero. While the dust arrived in Puerto Rico by June 22 increasing the PM₁₀ 550 nm scattering coefficient to over 300 Mm^-1 , it took several days to travel to the Texas coast, impacting Houston early on June 26 with hourly PM_2.5 exceeding 100 µg m^-3, and the 525 nm scattering coefficient exceeding 140 Mm^-1. The dust arrived in North Carolina and Illinois on the night of June 27 with the 550 nm scattering coefficients for PM₁₀ exceeding 200 and 60 Mm^-1, respectively. The presentation will discuss how this instrument suite confirms the dust impacts and compares to remote sensing. Dust transport simulated by a 3-D global model will also be used to interpret these measurements in terms of dust transport age, mixing, and surface vs. column impacts.