Demonstration of the 2D MAX-DOAS instrument: comparison with HSRL, MFRSR, and in situ aerosol optical properties during TCAP

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Description

The Two-Column Aerosol Project (TCAP) field intensive operational period (July 15– August 31) at Cape Cod, Massachusetts, provided an opportunity to evaluate a new passive remote sensor to measure trace gases and aerosol optical properties: the University of Colorado (CU) 2D scanning Multi Axis Differential Optical Absorption Spectroscopy (2D-MAX-DOAS) instrument. 2D-MAX-DOAS features an azimuth- and elevation-angle scanning telescope to measure scattered and direct sun light radiance spectra. These spectra are analyzed by DOAS non-linear least square fitting to retrieve trace gas slant column densities (SCD, i.e., NO2, HONO, HCHO, CHOCHO, BrO, IO, O4 SCDs, and Raman scattering probability). In a second step, aerosol extinction and trace gas vertical distributions are retrieved by constrained optimal estimation/regularization algorithms by inverse modeling of radiative transfer modeling (RTM).

The 2D MAX-DOAS was deployed and operated for six weeks at Cape Cod, Massachusetts, as part of TCAP. This deployment provides unique opportunities for comparisons with aerosol extinction profile measurements with in situ measured optical properties aboard the DOE’s G-1 aircraft, NASA Langley’s airborne high-spectral resolution lidar (HSRL), and aerosol optical depth by a collocated NOAA multifilter rotating shadowband radiometer (MFRSR).

The 2D-MAX-DOAS instrument is presented, as well as a retrieval to invert effective radius and complex refractive index of particles for monomodal logarithmic normal distribution derived from Mie-scattering calculations in the size range of 0.1–1um. Aerosol extinction retrieved from MAX-DOAS measurements is compared with extinction predicted by Mie theory to test the assumption of particle homogeneity and sphericity. The synergy of data provided by the DOE and NASA aircrafts, DOE’s ARM Mobile Facility (AMF), and Mobile Aerosol Observing System (MAOS) provide opportunities to evaluate 2D-GMAX-DOAS for use with (1) atmospheric radiation closure studies, (2) test retrievals of aerosol optical depth in the presence and absence of clouds, (3) measure trace gases and aerosol profiles in an often decoupled boundary layer, and (4) use 2D-MAX-DOAS to bridge between spatial scales probed by in situ sensors, aircraft, satellites, and those predicted by atmospheric models.