CHEMICAL AND OPTICAL-PROPERTIES OF MARINE BOUNDARY-LAYER AEROSOL-PARTICLES OF THE MID-PACIFIC IN RELATION TO SOURCES AND METEOROLOGICAL TRANSPORT

Incorporating the direct effect of tropospheric aerosol on climate int o global climate models involves coupling the optical properties of th e aerosol with its physical and chemical properties. This coupling is strengthened if the optical, physical, and chemical properties of the individual aerosol components are known as well as how these propertie s depend on the air mass source and synoptic scale meteorology. To rel ate properties of the aerosol components to air mass sources over a wi de range of meteorological conditions, two long latitudinal cruises we re conducted in the central Pacific Ocean from 55 degrees N to 70 degr ees S. Submicron non-sea-salt (nss) SO4= aerosol averaged about 35 to 40% of the submicron ionic mass as analyzed by ion chromatography and 6% of the total ionic mass, while supermicron nss SO4= aerosol contrib uted about 1% to the total ionic mass. About 1% of the remaining total ionic mass was composed of methanesulfonate and 90% was sea salt. Ion ic mass fractions of nss SO4= aerosol were highest in regions having t he longest marine boundary layer residence times or the largest source of marine or continental gas phase precursors. The calculated scatter ing by nss SO4= aerosol was highest in these same regions due to the d ependence of scattering on particle size and the concentration of nss SO4= in the submicron size range. The calculated scattering by submicr on sea salt was similar to that of the nss SO4= aerosol, indicating th at its contribution to scattering in the marine boundary layer can be significant or even dominant depending on its mass concentration. Mass scattering efficiencies for nss SO4= at 30% RH ranged from 4.3 to 7.5 m(2) g(-1) and for submicron sea salt from 3.5 to 7.7 m(2) g(-1). Mas s backscattering efficiencies for nss SO4= ranged from 0.41 to 0.58 m( 2) g(-1) and for submicron sea salt from 0.33 to 0.63 m(2) g(-1). Thes e values fall within the same range as others reported previously for the marine atmosphere.