资源环境科技发展态势分析平台

etween 2005 and 2012, U.S. emissions of nitrogen oxides (NOx) and sulfur dioxide (SO2) decreased by 42% and 62%, respectively. These species, as well as ammonia (NH3), are precursors of inorganic fine aerosols, which scatter incoming shortwave radiation and thus affect climate. Scaling aerosol concentrations to emissions, as might be done for near-term climate projections, neglects nonlinear chemical interactions. To estimate the magnitude of these nonlinearities, we conduct a suite of simulations with a chemical transport model and an off-line radiative transfer model. We find that the direct radiative effect (DRE) over the North American domain decreases by 59 and 160 mW m(-2) in winter and summer, respectively, between 2005 and 2012. The sensitivities of DRE to NOx and SO2 emissions increase, by 11% and 21% in summer, while sensitivity to NH3 emissions decreases. The wintertime sensitivity of DRE to NOx emissions is small in 2005 but is 5 times as large in 2012. Scaling radiative effects from 2005 to 2012 based on 2005 sensitivities overestimates the magnitude of the DRE of 7% and 6% of the U.S. attributable DRE in January and July, respectively. The difference between the changes in DRE and the changes in sensitivity suggests that scaling to SO2 emissions alone has so far been an accurate approximation, but it may not be in the near future. These values represent the level of accuracy that can be expected in adjusting aerosol radiative effects in climate models without chemistry.

Plain Language Summary Emissions of nitrogen oxides, sulfur dioxide, and ammonia contribute to atmospheric aerosols. These aerosols reflect and absorb light, influencing the total amount of sunlight (radiation) absorbed by the atmosphere, ocean, and land. Over the past decade, U.S. emissions nitrogen oxides and sulfur dioxide have decreased, influencing how aerosols and their climate impacts will respond to future emissions. We used an atmospheric chemistry model to estimate how much aerosol radiative effects responded to changes in emissions in 2005 and 2012. We found that nitrogen oxides have 5 times the influence on wintertime radiative effects in 2012 as in 2005. This influence has historically been small, and this increase makes its influence more similar to that of sulfur dioxide. The influence of sulfur dioxide has itself increased, by 11% in summertime, despite sulfur dioxide emissions decreasing. Our results suggest that climate studies may need to use revised aerosol concentrations to understand radiative effects in the near future.