Airborne in Situ Measurements of Aerosol Optical Properties and Particle Size Distributions on the East Coast of the U.S. and Their Comparison to MISR Aerosol Products

We measured in situ measurements vertical profiles and horizontal transects of aerosol optical and physical properties 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. These data are presented and compared to aerosol products derived from the Multi-angle Imaging Spectro-Radiometer (MISR) aboard NASA's Terra satellite. Most of the measurements were obtained in relatively clean air dominated by airflows that had passed over Canada and the northern Atlantic Ocean. We compare the results from two dates, 17 July and 2 August 2001 when reliable and coincident measurements were obtained from both platforms. Comparisons of the airborne measurements with remotely sensed aerosol parameters (single-scattering albedo [ωO], aerosol optical depth [AOD], and effective particle radius [reff]) derived from MISR were in good agreement. In the lower troposphere, airborne measurements resulted in ωO values (at a wavelength of 550 nm) consistently above 0.93 throughout the field experiment, indicating the dominance of weakly absorbing aerosol. Particle number size distributions are presented for transects at altitudes ~0.05 to 3.5 km above mean sea level. Particles with diameters (Dp) < 0.1 μm 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 down to ~1-4 km. There was minimal horizontal variability in ωO, AOD and accumulation mode size, but greater variability in particle number concentration. As a result, the resolution of the MISR aerosol retrieval (~17.6 km) was sufficient for capturing any significant horizontal variability in ωO, AOD, and reff during CLAMS. Overall, the MISR retrievals captured both the similarities and the differences between the ωO, AOD and reff of the aerosol measured on 17 July and 2 August.