V N Kapustin, T S Bates, D S Covert, D J Coffman and P K Quinn (NOAA/Pacific Marine Environmental Laboratory, 7600 Sand Point Way N.E., Seattle, WA 98115; and Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA, 98195; 206-526-6248; e-mail: bates@pmel.noaa.gov)
The goal of the International Global Atmospheric Chemistry (IGAC) Program’s first Aerosol Characterization Experiment (ACE-1) was to determine and understand the properties and controlling factors of the aerosol in the remote marine atmosphere that are relevant to radiative forcing and climate. A key question in terms of this goal and the overall biogeochemical sulfur cycle is what controls the formation, growth, and evolution of particles in the marine boundary layer? Non-sea-salt (nss) sulfate aerosol particles in the remote marine atmosphere are thought to have only one primary gaseous precursor, dimethylsulfide (DMS). It is not clear, however, if 1) the flux of DMS from the ocean to the atmosphere is sufficient to account for the total mass of nss sulfate aerosol and if 2) particle production occurs primarily in the marine boundary layer or the free troposphere.
To address these questions, simultaneous measurements of DMS, the aerosol chemical mass size distribution, and the aerosol number size distribution from 3 to 10,000 nm diameter were made on the NOAA ship Discoverer during ACE-1. Although the median DMS flux of 6 mmoles m^-2 d^-1 could support the total mass of nss sulfate aerosol in the marine boundary layer, the presence of ultra-fine (sub 20 nm) or "new" particles corresponded to cold frontal passages and periods of synoptic-scale subsidence and convective mixing between the free troposphere and the marine boundary layer. It is clear from these data that particle formation occurs in the free troposphere on large spatial and vertical scales and is not confined to regions of precursor gas emissions.