Relating Aerosol Profile and Column Measurements to Surface Concentrations: What Have We Learned from Discover-AQ?

Abstract:

One research goal of the Deriving Information on Surface Conditions from COlumn and VERtically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) mission was to determine sufficient column profile measurements to relate column integrated quantities such as Aerosol Optical Depth to surface concentrations. I will review the relationship between AOD and PM_2.5 at the surface. DISCOVER-AQ in Baltimore, the San Joaquin Valley, Houston and Denver revealed quite different conditions for determining this relationship. In each case, the surface reflectivity made determination of aerosol optical depth challenging, but upward looking columns of aerosol optical depth from sunphotometers provided confirmation of the AOD results from space. In Baltimore, AOD fields reflected PM_2.5 concentrations well. In California, however, the low boundary layer heights and dominance of nitrate and organic aerosols made the AOD fields less predictive of PM_2.5. In California and Colorado, hydration of the aerosol varied dramatically with aerosol type (especially smoke and dust) and revealed that without an understanding of the degree of aerosol hydration with aerosol composition, the relationship between AOD and PM_2.5 will continue to be a challenge. Model predictions in the Baltimore-Washington study are relatively disappointing in helping define the needed physics between the optical and microphysical properties. An overview of the measurements from DISCOVER-AQ which will help define the needed information in a more general case in the future will be given.