Cavity Ring-Down Measurements of Aerosol Optical Properties during the Asian Dust above Monterey Experiment and DOE Aerosol Intensive Operating Period

摘要

Aerosols have a significant effect on visibility, the radiation balance in the atmosphere, and can be a threat to human health. One of the biggest obstacles to a better understanding of these effects and an improved ability to model climate is an inadequate knowledge of the optical properties and the spatial distribution of atmospheric aerosols. Improvements in our knowledge of aerosol characteristics require improved in situ measurements of extinction coefficient and single-scattering albedo. This paper describes the use of continuous wave cavity ring down technology (CW-CRD) to address this problem. The innovations in this instrument, called Cadenza, are the use of CW-CRD to measure aerosol extinction coefficient with the simultaneous measurement of scattering coefficient. Combining these two parameters, one can obtain the single scattering albedo and absorption coefficient, both important aerosol properties. The use of two wavelengths (675 nm and 1550 nm) also allows us to obtain a quantitative idea of the size of the aerosol through the Angstrom exponent. The minimum sensitivity of this instrument is 1.5 × 10{sup}(-6) m{sup}(-1) (1.5 Mm{sup}(-1)). The small size and fast response time (seconds) of Cadenza makes it an ideal choice for both aircraft and ground-based studies. This instrument has recently successful participated in two missions in April and May 2003 aboard the CIRPAS Twin-Otter aircraft. These missions, Asian Dust Above Monterey (ADAM) and the DOE Aerosol Intensive Operating Period (IOP), had as objectives the study aerosol layers aloft, their transport, and radiative effects. These objectives matched the design goals of Cadenza extremely well and provided comparisons with other aerosol measurement instruments. Results from both missions will be presented in this paper.