The Advective Flux and Temporal Evolution of Aerosols from the Western Pacific Rim as Observed during TRACE-P

The 2001, NASA Transport and Chemical Evolution over the Pacific (TRACE-P) experiment was conducted during late winter and early spring, the time of year when eastward transport of dust and pollution from southern and central Asia reaches a maximum. From bases of operation in Hong Kong, Japan, and Hawaii, extensive measurements of trace species concentrations and characteristics were made from aboard a P-3B and DC-8 aircraft as they flew coordinated sampling missions within air masses at varying distances from the Asian coast and at altitudes ranging from near surface to over 12 km. Data recorded aboard the DC-8 included total condensation nuclei (CN) number densities and fractional volatility; aerosol size distributions, composition and optical properties; and multi-wavelength profiles of polarized, aerosol backscatter. Examining these data in light of simultaneous meteorological and chemical species measurements, we have calculated the advective flux and mean values of aerosol mass and physical properties at various locations within the Western Pacific Basin. At distances >100 km offshore, we find that the highest fluxes of sub-micron particles occurred below 2 km in the region downwind of Shanghai. These air masses exhibited CN concentrations approaching 50,000 cm^-3 and visible scattering coefficients in excess of 200 Mm^-1. For near-shore sampling between 26° and 36°N within this height range, these parameters averaged ~8,000 cm^-3 and 130 Mm^-, respectively, . As a result of dilution, surface deposition, and precipitation scavenging, these values rapidly diminished during eastward transport so that parcels sampled at low altitudes >1500 km from land typically contained ~1000 cm^-3 CN and exhibited scattering coefficients <30 Mm^-1. Because of the decreased strength of loss processes and greater atmospheric stability, parcels sampled in the 2- to 7-km height range were more apt to maintain their initial aerosol signatures during long-range transport.