A comparison of the aerosol thickness derived from ground-based and airborne measurements

The extinction optical thickness of particles obtained from scattering and absorption coefficients measured by an airborne integrating nephelometer an d particle soot absorption photometer, respectively, is compared with the a erosol optical thickness derived from a ground-based multifilter rotating s hadowband radiometer, a Sun photometer, and a Raman lidar for 9 days. These 9 days are selected from intensive operation periods of the Atmospheric Ra diation Measurement in April 1997, September 1997, and August 1998 at the s outhern Great Plains. For April 1997 and September 1997 cases the differenc e between the extinction optical thickness of particles estimated from vert ical profiles and the extinction optical thickness of aerosol derived from the multifilter rotating shadowband radiometer is not significant. For Augu st 1998 cases when the boundary layer relative humidity is higher than Apri l 1997 and September 1997 cases, the extinction optical thickness of partic les is 0.03 to 0.07 less than the extinction optical thickness of aerosol. The difference corresponds to 25% to 31% of the extinction optical thicknes s of aerosol. Based on these comparisons, the upper and lower limits of the single-scattering albedo of particles present in the lower part of troposp here are 0.97 and 0.84, respectively.