Airborne minerals and related aerosol particles: Effects on climate and the environment
Abstract
Aerosol particles are ubiquitous in the troposphere and exert an important influence on global climate and the environment. They affect climate through scattering, transmission, and absorption of radiation as well as by acting as nuclei for cloud formation. A significant fraction of the aerosol particle burden consists of minerals, and most of the remainder— whether natural or anthropogenic—consists of materials that can be studied by the same methods as are used for fine-grained minerals. Our emphasis is on the study and character of the individual particles. Sulfate particles are the main cooling agents among aerosols; we found that in the remote oceanic atmosphere a significant fraction is aggregated with soot, a material that can diminish the cooling effect of sulfate. Our results suggest oxidization of SO2 may have occurred on soot surfaces, implying that even in the remote marine troposphere soot provided nuclei for heterogeneous sulfate formation. Sea salt is the dominant aerosol species (by mass) above the oceans. In addition to being important light scatterers and contributors to cloud condensation nuclei, sea-salt particles also provide large surface areas for heterogeneous atmospheric reactions. Minerals comprise the dominant mass fraction of the atmospheric aerosol burden. As all geologists know, they are a highly heterogeneous mixture. However, among atmospheric scientists they are commonly treated as a fairly uniform group, and one whose interaction with radiation is widely assumed to be unpredictable. Given their abundances, large total surface areas, and reactivities, their role in influencing climate will require increased attention as climate models are refined.
Footnotes
-
↵ * To whom reprint requests should be addressed. e-mail: pbuseck{at}asu.edu.
-
↵ † Present address: Department of Earth and Environmental Sciences, University of Veszprém, Veszprém, POB 158, H8201 Hungary.
-
This paper was presented at the National Academy of Sciences colloquium “Geology, Mineralogy, and Human Welfare,” held November 8–9, 1998 at the Arnold and Mabel Beckman Center in Irvine, CA.
-
↵ ‡ Aerosol particles, to the extent they consist of nonanthropogenic homogeneous inorganic solids of more or less uniform composition and have ordered structures, fit generally accepted definitions of minerals. However, except for the title, in this manuscript we follow the usage common among atmospheric scientists and use “minerals” to refer to materials that once resided on Earth’s land surface.
-
↵ § Here we use “sulfate” for particles that consist purely or predominantly of sulfates and are formed in the atmosphere by either homogeneous or heterogeneous reactions involving SO2 gas. They have compositions ranging from H2SO4 to (NH4)2SO4. Sea-salt sulfate and the NSS sulfate formed by conversion of the original sea-salt particles are not considered in this section.
- ABBREVIATIONS:
- CCN,
- cloud condensation nuclei;
- TEM,
- transmission electron microscope;
- SEM,
- scanning electron microscope;
- MBL,
- marine boundary layer;
- FT,
- free troposphere;
- NSS,
- non-sea salt;
- AFM,
- atomic force microscopy;
- ACE,
- Aerosol Characterization Experiments;
- FeLINE,
- experiments in the equatorial Pacific;
- ASTEX/IMAGE,
- experiments in the North Atlantic
- Copyright © 1999, The National Academy of Sciences
