GMAXDOAS

The University of Colorado has developed an innovative passive remote sensor, the CU 2D scanning ground Multi AXis Differential Optical Absorption Spectroscopy (2D-GMAX-DOAS) instrument that 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). 2D-GMAX-DOAS retrievals are based exclusively on relative intensity changes, i.e., do not require absolute radiance calibrations, which minimizes the need for instrument maintenance; the instrument can be remote controlled via internet, operates quasi-autonomously, and is optimized for measurements in remote locations for extended periods of time. In addition, the CU-LED-CE-DOAS instrument provides in-situ observations for NO2, CHOCHO and O4 near the surface (within the surface roughness layer).

The CU 2D-GMAX-DOAS and LED-CE-DOAS instruments were operated during the TCAP field intensive period (15 July to 31 August 2012) at Cape Cod, MA, where ground-based aerosol measurements made with the DOE Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) and Mobile Aerosol Observing System (MAOS) provide an opportunity for 1) atmospheric radiation closure studies (incl. correction of 2D-GMAX-DOAS derived NO2 vertical columns in MFRSR retrievals); 2) test retrievals of aerosol optical depth by 2D-GMAX-DOAS and compare with Cimel sunphotometer, and MFRSR in the presence and absence of clouds; and 3) study secondary organic aerosol (SOA) formation from processing of glyoxal in cloud and aerosol water by combining experimental observations of glyoxal by CU GMAX-DOAS and CU LED-CE-DOAS with numerical models. 2D-GMAX-DOAS column observations bridge between spatial scales probed by in-situ sensors, satellites and those predicted by atmospheric models. The TCAP experiment presents the first field deployment of 2D-GMAX-DOAS outside Boulder

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