Modeling Optical Properties of Aerosols Using Microphysical Retrievals from Air Quality Models

The New York Metropolitan area is considered "unhealthy for sensitive groups" when measured with density populations of PM 2.5 according to standards set by the Environmental Protection Agency (EPA, 1996). In response the EPA has mandated a system to provide predictions of air quality just like the National Weather Service is mandated to provide weather forecasts. One model we are testing is the Community Multiscale Air Quality (CMAQ). Given emission inventories and meteorology data collected by surface, CMAQ attempts to model the extremely complex physics and chemistry of aerosol production and transport. The problem comes with the verification of CMAQ output in that is the model a reliable tool in aerosol prediction and monitoring. Predictions from CMAQ can be verified by using aerosol sampling devices at the surface but the model should also be accurate at high altitudes based on air transport theories. At the City College of New York we are in a unique situation to study the CMAQ models because of our urban setting (aerosol density) and having instruments that can verify Aerosol Optical Depth (AOD) and height. We can use remote sensing and our in house instrumentation to measure aerosol optical properties such as extinction and backscatter. These optical measurements can then be compared to CMAQ predictions if we know how to convert aerosol information (mass, size, refractive index) into optical information. We can then verify the data with our own sky radiometer, measuring total column optical depth, and our LIDAR which measures backscatter directly.