Airborne minerals and related aerosol particles: Effects on climate and the environment

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.

Correlations between the satellite-derived seasonal cycle of phytoplankton biomass and aerosol optical depth in the Southern Ocean: Evidence for the influence of sea ice

The relationship between the production of dimethylsulfide (DMS) in the upper ocean and atmospheric sulfate aerosols has been confirmed through local shipboard measurements, and global modeling studies alike. In order to examine whether such a connection may be recoverable in the satellite record, we have analyzed the correlation between mean surface chlorophyll (CHL) and aerosol optical depth (AOD) in the Southern Ocean, where the marine atmosphere is relatively remote from anthropogenic and continental influences. We carried out the analysis in 5-degree zonal bands between 50 degrees S and 70 degrees S, for the period ( 1997 - 2004), and in smaller meridional sectors in the Eastern Antarctic, Ross and Weddell seas. Seasonality is moderate to strong in both CHL and AOD signatures throughout the study regions. Coherence in the CHL and AOD time series is strong in the band between 50 degrees S and 60 degrees S, however this synchrony is absent in the sea-ice zone (SIZ) south of 60 degrees S. Marked interannual variability in CHL occurs south of 60 degrees S, presumably related to variability in sea-ice production during the previous winter. We find a clear latitudinal difference in the cross correlation between CHL and AOD, with the AOD peak preceding the CHL bloom by up to 6 weeks in the SIZ. This suggests that substantial trace gas emissions ( aerosol precursors) are being produced over the SIZ in spring ( October - December) as sea ice melts. This hypothesis is supported by field data that record extremely high levels of sulfur species in sea ice, surface seawater, and the overlying atmosphere during ice melt.