Sources and Properties of Atmospheric Aerosol in Texas: DISCOVER-AQ Measurements and Validation
Tropospheric air quality is degraded by local aerosol sources and gas phase precursors as well as aerosol transported over long distances. While the availability of recent satellites such as the Moderate-resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) offer improved accuracy and global coverage of aerosol, such measurements still rely on broad assumptions in determination of aerosol source and composition. During the fall of 2013, the Houston area was the site of the 2nd field intensive of the NASA Deriving Information on Surface conditions from COlumn and VERtically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign. During DISCOVER-AQ, this project's research team operated a new scattering instrument, the Cloud and Aerosol Spectrometer with Polarization (CASPOL), which measures the depolarization ratio of individual particles in the aerosol population. The polarization capabilities of CASPOL facilitate an effective approach to validate spaceborne aerosol retrieval, particularly CALIOP aerosol type classification. The CASPOL was operated on top of the 60 m tall Moody Tower (MT) on the University of Houston campus, a central urban location and site of many complementary measurements during DISCOVER-AQ. In this study, the CASPOL data set will be analyzed to determine the concentration, size distribution, and optical properties of aerosol from the wide variety of sources, including urban pollution sources from downtown Houston, the industrial Ship Channel, and transported aerosol. Combined with additional measurements of organic carbon, black carbon and ozone, the CASPOL data set provides an opportunity to determine the primary aerosol sources and impacts of aging due to ozone modified aerosol optical properties. These in-situ data will be compared to MODIS and CALIOP aerosol measurements to determine the sensitivity of remote sensing to changes in surface aerosol properties and air quality. Results from the project will improve the linkage between column observations provided by satellite instruments and near-surface atmospheric composition, which is relevant to air quality and human health in the short term and the relationship between future air quality and climate.