Hygroscopic Growth of Organic Atmospheric Aerosols
Lynn Russell
Scripps Institute of Oceanography

Recent measurements of organic functional groups illustrate that the organic fraction of particles differs widely with region and altitude.  More polar organic compounds tend to be more water soluble, increasing the hygroscopicity of aerosol particles. Differences in the organic composition of particles result from a combination of source variability and photochemical reactions, and these differences change the role of aerosol particles. Particles measured in the Caribbean in July 2000 show more polar organic compounds in the free troposphere, consistent with photochemical aging of emissions transported from Central and Eastern Europe. Similar measurements of organic compounds in the Sea of Japan in April 2001 show more variability with altitude, consistent with the variety and regional range of emissions. Parameterized estimation methods show that the higher fractions of carbonyl groups present in these samples take up more water than the larger masses of less soluble organic compounds at lower altitudes. The increase in polarity and water solubility associated with some high altitude aerosol layers provide evidence that particles attributed to long-range transport have been aged by photochemical processes that increase their hygroscopicity.

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