A Pacific Aerosol Survey. Part I: A Decade of Data on Particle Production, Transport, Evolution, and Mixing in the Troposphere*

Abstract

Integration of extensive aerosol data collected during the past decade around the Pacific basin provides a preliminary assessment of aerosol microphysics for this region and cycling of aerosol in the troposphere. These include aircraft-based data collected as part of numerous field experiments supported by the National Aeronautics and Space Administration (NASA), the National Science Foundation (NSF), and the National Oceanic and Atmospheric Administration (NOAA) [Global Backscatter Experiment (GLOBE), First Aerosol Characterization Experiment (ACE-1), Pacific Exploratory Mission (PEM)-Tropics A and B]. Although these experiments had diverse goals, most included extensive data on aerosol size distributions, optical properties (light scattering and light absorption), and chemistry. Vertical profiles of aerosol concentration, size distribution, and light scattering were used to characterize vertical structure from 70°S to 70°N. The in situ data are placed in the context of meteorological regimes over the Pacific as well as processes associated with particle formation, growth, and evolution, and include dust, pollution, sea salt, sulfates, and clean cloud–processed air. The Tropics commonly have low aerosol mass but very high number concentrations in the upper free troposphere (FT) that appear to form from sulfuric acid (nucleation) in convective regions and near cloud edges. These age and subside to become effective cloud condensation nuclei (CCN) when mixed into the marine boundary layer. Fewer number but larger aerosol are more evident in the midlatitude FT. These can often be internally mixed and with a nonvolatile core indicative of black carbon with volatile components (sulfate, organics, etc.). In the North Pacific springtime a combustion-derived aerosol is frequently found associated with the same meteorology that transports “dust events.” Both constituents may dominate the scattering and absorption properties of the aerosol even though the increase in large dust particles in such events generally dominates the mass. The FT in the subtropics tends to exhibit frequent and marked transitions and mixing between these clean and continental aerosol types.