Vaishali Naik and Michael Oppenheimer continued to investigate the linkages between air pollution and climate change. They examined the sensitivity of global radiative forcing to the geographical location of biomass-burning emissions, and are also laying the foundations for a study of the impacts of ethanol on air quality and climate.

Reducing biomass burning emissions has been estimated to cause a short-term warming (by reducing reflective aerosols), but a long-term cooling from reducing CO2 (particularly by avoiding permanent deforestation) and other greenhouse gases. Reducing the 90% of global biomass-burning emissions attributed to human activities has thus been proposed as a control strategy for mitigating climate change.

Using global three-dimensional atmospheric chemistry and radiative transfer models, the researchers assessed the sensitivity of global radiative forcing to the location of biomass burning by considering the effects of a 10% reduction in ozone precursor and aerosol emissions from major biomass burning regions of the world. They concluded that global radiative forcing due to biomass burning is most sensitive to the amount of biomass burned in tropical regions, particularly the Indian subcontinent. Their analysis also showed that marginal reductions in both short-lived ozone precursors and aerosol species yield negative global radiative forcing, implying a cooling tendency (although the sign of radiative forcing due to biomass burning aerosols is highly uncertain).

Naik and Oppenheimer will further examine the long-range transport of ozone to and from the Indian subcontinent to provide a better understanding of the influence of ozone precursor emissions on surface air quality in neighboring countries. Such source-reception relationships can then potentially be used to design a regional regime to control air pollution in South Asia.

This year, Naik and Oppenheimer, in collaboration with GFDL scientists, will also perform research to advance our understanding of the present-day atmospheric budget of ethanol and its implications for global atmospheric chemistry. The atmospheric concentration of ethanol, an oxygenated volatile organic compound (OVOC), is expected to increase as use of ethanol as a fuel increases worldwide. In addition to the potentially adverse impacts on regional air quality, enhanced ethanol concentrations may also influence background tropospheric chemistry and climate.

There is currently a large discrepancy between the observed and simulated atmospheric ethanol concentrations over the U.S. To improve simulations, researchers will first assess the global atmospheric budget and distribution of ethanol, which will lay the groundwork for investigating the potential impacts of future increases in ethanol use on air quality and climate. This will provide us with a much needed understanding of the role of ethanol in atmospheric chemistry and is a critical first step to designing alternative domestic fuel strategies that do not compromise climate and air quality objectives.