Aerosol Optical Properties and Particle Size Distributions on the East Coast of the United States Derived from Airborne In Situ and Remote Sensing Measurements

Abstract

Airborne in situ measurements of vertical profiles and horizontal transects of aerosol optical and physical properties, obtained during the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) field campaign off the East Coast of the United States during the summer of 2001, are presented. Most of the measurements were obtained in relatively clean air dominated by airflows that had passed over Canada and the northern Atlantic Ocean. Results from the 17 July and 2 August 2001 flights are presented; on these days, the aerosol loading was relatively high. In the lower troposphere, ?0 values at a wavelength of 550 nm were consistently above 0.93 throughout the field experiment, indicating the dominance of weakly absorbing aerosol. Particle number size distributions are presented and discussed for transects at altitudes ?0.05?3.5 km above mean sea level. Particles with diameters (Dp) <0.1 ?m made up the majority of the aerosol number. Accumulation mode particles dominate the number size, surface area, and volume distributions. The variability of optical and physical aerosol parameters was analyzed on horizontal scales of ?1?4 km. There was little horizontal variability in the single-scattering albedo (?0), aerosol optical depth (AOD), and accumulation mode size, but greater variability in particle number concentration. Comparisons of the airborne measurements with remotely sensed aerosol parameters, such as ?0 and effective particle radius (reff), derived from the Multiangle Imaging Spectroradiometer (MISR) aboard the Terra satellite were generally in good agreement. Overall, the MISR retrievals captured both the similarities and the differences between the properties of the aerosols measured on 17 July and 2 August.