Tropospheric aerosols: Size-differentiated chemistry and large-scale spatial distributions: Fid-Bau Portal

Tropospheric aerosols: Size-differentiated chemistry and large-scale spatial distributions

Hidy, George M. / Mohnen, Volker / Blanchard, Charles L.

Worldwide interest in atmospheric aerosols has emerged since the late 20th century as a part of concerns for air pollution and radiative forcing of the earth's climate. The use of aircraft and balloons for sampling and the use of remote sensing have dramatically expanded knowledge about tropospheric aerosols. Our survey gives an overview of contemporary tropospheric aerosol chemistry based mainly on in situ measurements. It focuses on fine particles less than 1–2.5 µm in diameter. The physical properties of particles by region and altitude are exemplified by particle size distributions, total number and volume concentration, and optical parameters such as extinction coefficient and aerosol optical depth. Particle chemical characterization is size dependent, differentiated by ubiquitous sulfate, and carbon, partially from anthropogenic activity. Large-scale particle distributions extend to intra- and intercontinental proportions involving plumes from population centers to natural disturbances such as dust storms and vegetation fires. In the marine environment, sea salt adds an important component to aerosols. Generally, aerosol components, most of whose sources are at the earth's surface, tend to dilute and decrease in concentration with height, but often show different (layered) profiles depending on meteorological conditions. Key microscopic processes include new particle formation aloft and cloud interactions, both cloud initiation and cloud evaporation. Measurement campaigns aloft are short term, giving snapshots of inherently transient phenomena in the troposphere. Nevertheless, these data, combined with long-term data at the surface and optical depth and transmission observations, yield a unique picture of global tropospheric particle chemistry.

Aerosols in the troposphere incorporate issues of air pollution exposing humans and ecosystems, and global forcing of the climate of the atmosphere. Fundamental physicochemical knowledge of suspended particles of different sizes is essential to addressing these as technical issues across the world. Current literature informs policymakers about the nature of tropospheric aerosols and their global scale spatial and temporal distributions. With this knowledge, cooperative programs for addressing environmental issues across national borders can be constructed with insight into sources and receptors of pollution and natural air chemistry. For the United States the policy-relevant background for particles is better defined from this work.

Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air & Waste Management Association for detailed data tables, color graphics, summary dynamics, and additional references.