Vertical profile retrievals of trace gases and aerosol optical properties by CU GMAX-DOAS

Description

During the Two-Column Aerosol Project (TCAP) field campaign, the University of Colorado Ground based Multi AXis DOAS instrument (CU GMAX-DOAS) will be deployed at Cape Cod to provide simultaneous retrievals of aerosol optical properties and trace gas vertical profiles with a single portable instrument. CU GMAX-DOAS allows the study of horizontal and vertical aerosol gradients and decoupling of trace gas and aerosol vertical extinction profiles. A novel telescope was developed and is presented here. It collects solar stray light in any elevation/azimuth angle pair and is capable of direct sun tracking. The telescope aims to facilitate the determination of aerosol optical properties, i.e., asymmetry parameter and single-scattering albedo, along with the determination of absolute Raman scattering probability (RSP), i.e., the probability that an observed photon has undergone a rotational Raman scattering event, from recording both scattered light radiance spectra and direct sun spectra. Simultaneously, the vertical column density (VCD) of trace gases like nitrogen dioxide (NO2), nitrous acid (HONO), formaldehyde (HCHO), glyoxal (CHOCHO), bromine oxide (BrO), iodine oxide (IO), and oxygen dimers (O4) can be measured with the same instrument. The poster presents first tests of the novel telescope at the University of Colorado at Boulder that we plan to deploy during TCAP for the first extended field deployment. We plan to compare CU GMAX-DOAS with ARM instruments such as the Cimel sunphotometer and multifilter rotating shadowband radiometer (MFRSR), as well as in situ measurements, and possibly airborne instruments such as the high spectral resolution lidar (HSRL) and 4STAR during the intensive aircraft period. CU GMAX-DOAS adds trace gases to the extensive suite of aerosol measurements planned. In particular, the cloud processing of gases like glyoxal forms secondary organic aerosol (SOA) in clouds and aerosol water. Another aspect consists in exploring the capabilities for retrievals of aerosol optical properties in the presence of clouds.