Remote sensing of fine and coarse mode atmospheric aerosols using ground-based sun-photometry

Abstract

We recently developed a new version of our analysis algorithm for Multi-Filter Rotating Shadowband Radiometer (MFRSR) data that allows us to retrieve fine mode and coarse mode aerosol optical thickness as well as the effective radius of the fine mode. Our retrieval products also include time series of column amounts of ozone and nitrogen dioxide. The algorithm has been tested using a multi-year dataset from the local MFRSR network at the DOE Atmospheric Radiation Measurement (ARM) Program site in Southern Great Plains (SGP). Here we present an overview of the retrieval algorithm and validate its performance through comparison of our MFRSR retrieval products with the corresponding AERONET almucantar retrieval results derived from a CIMEL sunphotometer co-located with the MFRSR at the SGP Central Facility. A constrained variant of the retrieval algorithm (assuming zero nitrogen dioxide column values) is described in detail. We use this variant of the algorithm to derive the range of physically justified values of the fine mode effective radius and for comparison with AERONET particle size retrievals. A multi-instrument, multi-year, MFRSR dataset from the SGP Extended Facilities is used to examine geographical and seasonal variability of aerosol properties. We find a correspondence between the geographical variation in fine mode particle size and aerosol composition (nitrates vs. sulfates) as measured by National Atmospheric Deposition Program. A similar correspondence in terms of temporal variability exists between our retrievals and in-situ measurements of aerosol composition made by NOAA Pacific Marine Environmental Laboratory (PMEL) at SGP Central Facility.