资源环境科技发展态势分析平台

Tropospheric ozone (O-3), a harmful secondary air pollutant, can affect the climate via direct radiative forcing and by modifying the radiative forcing of aerosols through its role as an atmospheric oxidant. Moreover, O-3 exerts a strong oxidative pressure on the biosphere and indirectly influences the climate by altering the materials and energy exchange between terrestrial ecosystems and the atmosphere. However, the magnitude by which O-3 affects the global budgets of greenhouse gases (GHGs: CO2, CH4, and N2O) through altering the land-atmosphere exchange is largely unknown. Here we assess the sensitivity of these budgets to tropospheric O-3 pollution based on a meta-analysis of experimental studies on the effects of elevated O-3 on GHG exchange between terrestrial ecosystems and the atmosphere. We show that across ecosystems, elevated O-3 suppresses N2O emissions and both CH4 emissions and uptake, and has little impact on stimulation of soil CO2 emissions except at relatively high concentrations. Therefore, the soil system would be transformed from a sink into a source of GHGs with O-3 levels increasing. The global atmospheric budget of GHGs is sensitive to O-3 pollution largely because of the carbon dioxide accumulation resulting from suppressed vegetation carbon uptake; the negative contributions from suppressed CH4 and N2O emissions can offset only similar to 10% of CO2 emissions from the soil-vegetation system. Based on empirical data, this work, though with uncertainties, provides the first assessment of sensitivity of global budgets of GHGs to O-3 pollution, representing a necessary step towards fully understanding and evaluating O-3-climate feedbacks mediated by the biosphere.