Retrieving aerosols, ozone, and nitrite using MFRSR, RSS, and CIMEL data.

摘要

The ability to measure gas and aerosol amounts, and aerosol particle sizes, from data obtained by sun photometers needs improvement. The retrieval strategies for two widely used sun photometers, the Multi-Filter Rotating Shadowband Radiometer (MFRSR) and the CIMEL Electronique 318A Spectral Radiometer, disagree on whether to measure gases simultaneously with aerosols or simply use climatological values, and on how many aerosol modes are necessary to explain the aerosol extinction. A crucial issue for the MFRSR is that errors in the retrieval of gas amounts result in errors in the retrieved aerosol particle size. The Rotating Shadowband Spectroradiometer (RSS) has much higher spectral resolution than either the MFRSR or the CIMEL. This results in superior gas measurement, but the Ring effect can interfere with gas measurements if ignored. This study uses data taken between July 1999 and July 2000 from an MFRSR, RSS, and CIMEL device co-located at the Southern Great Plains (SGP) site in Oklahoma.; An Empirical Orthogonal Function (EOF) analysis is performed on all three data sets, resulting in five conclusions. First, the information obtainable from these devices is limited.{09}Second, the aerosol size distribution is bimodal. Third, the RSS can best separate gases from aerosols, but cannot otherwise retrieve aerosol information significantly better. Fourth, the fine aerosol mode is measurable by all three devices, but additional infrared wavelength ranges would better define the coarse mode. Fifth, subtle defects within the data show up in the EOF analysis.; Retrievals are performed, using existing techniques for the MFRSR and CIMEL, and newly devised techniques for retrieving aerosols and NO₂ with RSS data. The assumption of unimodal size distributions causes large overestimations of NO₂ amounts and the aerosol effective radius, and cannot explain the spectral curves in the data. Bimodal retrievals must not overanalyze the data, or important seasonal cycles could get masked. Finally, the accuracy of MFRSR retrievals can be improved by replacing the filter at 670 nm with another at a different wavelength, and by altering the assumptions inherent in the retrieval strategy.