MFRSR instrument calibration and applications to source attribution of aerosols during the 2011 BNL IOP

Understanding of chemical, physical, and radiative processes of atmospheric aerosols – emissions, transport, aging, and removal – is of major importance in studies of climate change, visibility, and air quality affecting human health and welfare. This paper presents aerosol optical properties retrieved with a Multifilter Rotating Shadowband Radiometer (MFRSR) and the source attribution based on the NOAA HYSPLIT model and in situ aerosol chemical composition analysis during the Aerosol Life Cycle IOP at Brookhaven National Laboratory, Long Island, NY, during July, 2011. The MFRSR is calibrated using two different techniques. These techniques, which are based directly on observation data, are used to determine the aerosol optical depths (AODs). The instrument calibration constants are validated internally against each other as well as against a technique based on top-of-atmosphere solar spectral irradiance convolved with the MFRSR filter response. In addition, the aerosol optical parameters obtained from the MFRSR are assessed against the same parameters retrieved with a recently calibrated Cimel sunphotometer collocated with the MFRSR instrument. These comparisons indicate agreement of AOD determined by the two instruments within 0.02 at shorter wavelengths and 0.01 at longer wavelengths. The separation of AODs by size modes reveals several instances of high loading of fine aerosols (0.1-1 µm diameter). Analysis of optical and physical properties and chemical composition of the aerosols together with the HYSPLIT analysis indicates that the principal source of high concentrations of fine aerosols observed during July 20-24 was forest fires in western Canada, which were documented by the Canadian Forest Service and observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the Terra Satellite.