BIOGENIC AEROSOLS AND CARBON SEQUESTRATION

摘要

There is experimental evidence that forests increase their carbon sequestration efficiency with increasing diffuse photosynthetically active irradiance (PAR) (Gu et al., 1999; Roderick et al., 2001). Increased levels of diffuse irradiance can be due to increases in cloudiness and atmospheric turbidity. Over continental eastern North America, one reason for an increase in atmospheric turbidity may be related to greater loads of fine aerosols resulting from the photo-oxidation of biogenic hydrocarbons. Compared to 50 years ago, eastern North America is more forested, thus providing greater potential for hydrocarbon production. These forest ecosystems release into the atmosphere biogenic hydrocarbons such as terpenes that upon oxidation by such compounds as ozone and hydroxyl radicals may form reaction products that can condense to form secondary organic aerosols (SOAs). In this study, we first evaluate the hypothesis that airborne aerosols, resulting from phytogenic sources, generate high levels of diffuse irradiance, which could in turn contribute to enhanced carbon sequestration, thereby driving a two-way feedback loop between forests and carbon uptake. Secondly, biogenic aerosols modify the radiative balance of the Earth's troposphere by backscattering and absorbing incoming shortwave irradiance and by absorbing outgoing longwave irradiance. Using a physically based model (Pilinis, 1989), we investigate changes in both quantity and quality of incoming solar irradiance . based on measured aerosol number size distributions and light levels. The hypothesis here is that once in the atmospheric boundary layer, SOAs modify solar irradiance through Mie scattering.