Aerosol optical closure and long-term MAX-DOAS observations

Christopher Lee,
ANYL 3rd year student, Volkamer group

"Aerosols remain a major source of uncertainty in the global radiative budget. Studies that combine vertically-resolved measurements of aerosol size distributions and refractive index (inferred from aerosol composition measurements) are needed to assess our understanding of multispectral aerosol optical closure. Here we use data from the NASA airborne HSRL-2 instrument, which retrieves aerosol extinction profiles at 355, 532, and 1064 nm from backscatter measurements. The dataset we use is from the Two-Column Aerosol Project (TCAP) in July 2012, which deployed two research aircraft above the DoE ARM mobile facility at Cape Cod, MA. This dataset is reanalyzed here to investigate the effects of aerosol water on dry aerosol size and composition, and our ability to constrain Mie calculations to obtain multispectral optical closure.

High-altitude ground-based remote sensing is well-suited for long-term profile measurements of trace gases and aerosols, and provides unique sensitivity to the free troposphere. An example of this is the University of Colorado Multi-AXis Differential Optical Absorption Spectroscopy (CU MAX-DOAS) instrument, which measures vertical profiles of trace gases (BrO, IO, HCHO, CHOCHO, NO2, O3, SO2, H2O, etc.) and aerosols. Since February 2017, two CU MAX-DOAS instruments have operated continuously at Mauna Loa Observatory, Hawaii (155.578 W, 19.539 N, 3397 msl) and Maido Observatory, Reunion Island (55.384 E, 21.080 S, 2160 msl), respectively. In March 2021, a third CU MAX-DOAS instrument was deployed at Storm Peak Laboratory (106.744 W, 40.455 N, 3209 msl) in Steamboat Springs, Colorado. Leveraging the data from these three measurement sites, the vertically-resolved spatiotemporal variation of trace gases and aerosols can be characterized in both hemispheres."