Anthropogenic Perturbations of Biogenic Aerosols: Climate Impacts and Feedbacks

Aerosols have been identified as a major uncertainty in climate forcing due to direct and indirect effects. Both scattering and absorption of radiation is of concern in the direct effect, and aerosols acting as cloud condensation nuclei (CCN) leads to the indirect effect as the aerosols impact cloud formation and type. Biogenic carbonaceous aerosol sources, as indicated by 14C content, have been found to be major contributors in both primary and secondary organic aerosols on regional scales. The secondary organic aerosol precursors from biogenic emissions include isoprene, monoterpenes, and sesquiterpenes that react rapidly with OH, nitrate radical, and ozone. All of these oxidants are increased by the increased emissions of NOx from anthropogenic combustion sources. This chemistry will be reviewed and the evidence for these oxidized products contributing to enhanced aerosol absorption in both the UV and IR regions will be presented. The potential changes in these emissions due to climate change will also be addressed. These include earlier springs, longer growing seasons, and higher temperatures leading to enhanced emission rates anticipated with climate change. The potential for these biogenic secondary organic aerosols as sources of dissolved organic carbon will also be presented and the connections to aqueous systems, including cloud droplets, will be discussed in terms of their surfactant properties. The potential for increased biogenic aerosols from agricultural activities (direct and from burning of stubble) will also be briefly noted in terms of the possible development of larger bio-fuel production as an alternative energy source.

This work is supported by the Office of Science (BER) U.S. Department of Energy under Grant No. DE-FG02-07ER6428, as part of DOE Atmospheric Systems Research (ASR).