Tennessee Valley Authority, P.O. Box 1010, Muscle Shoals, Alabama 35662-1010, USA.
Environ Sci Technol. 2011 Jun 1;45(11):4817-23. doi: 10.1021/es103645m. Epub 2011 May 5.
The relative roles of natural and anthropogenic sources in determining ozone and fine particle concentrations over the continental United States (U.S.) are investigated using an expanded emissions inventory of natural sources and an updated version of the Community Multiscale Air Quality (CMAQ) model. Various 12-month CMAQ simulations for the year 2002 using different sets of input emissions data are combined to delineate the contributions of background pollutants (i.e., model boundary conditions), natural emissions, anthropogenic emissions, as well as the specific impacts of lightning and wildfires. Results are compared with observations and previous air quality model simulations. Wildfires and lightning are both identified as contributing significantly to ozone levels with lightning NO(x) adding as much as 25-30 ppbV (or up to about 50%) to surface 8-h average natural O(3) mixing ratios in the southeastern U.S. Simulated wildfire emissions added more than 50 ppbV (in some cases >90%) to 8-h natural O(3) at several locations in the west. Modeling also indicates that natural emissions (including biogenic, oceanic, geogenic and fires) contributed ≤ 40% to the annual average of total simulated fine particle mass over the eastern two-thirds of the U.S. and >40% across most of the western U.S. Biogenic emissions are the dominant source of particulate mass over the entire U.S. and wildfire emissions are secondary. Averaged over the entire modeling domain, background and natural ozone are dominant with anthropogenically derived ozone contributing up to a third of the total only during summer. Background contributions to fine particle levels are relatively insignificant in comparison. Model results are also contrasted with the U.S. Environmental Protection Agency (EPA) default values for natural light scattering particle concentrations to be used for regional haze regulatory decision-making. Regional differences in EPA guidance are not supported by the modeling and EPA uncertainty estimates for default values are far smaller than the modeled variability in natural particle concentrations.
使用扩展的自然源排放清单和更新的社区多尺度空气质量（CMAQ）模型，研究了自然和人为源在确定美国大陆地区臭氧和细颗粒物浓度中的相对作用。结合 2002 年使用不同输入排放数据集的 12 个月 CMAQ 模拟结果，以描绘背景污染物（即模型边界条件）、自然排放、人为排放以及闪电和野火的具体影响。结果与观测值和先前空气质量模型模拟值进行了比较。结果表明，闪电和野火都对臭氧水平有显著贡献，闪电产生的 NO(x) 对美国东南部地表 8 小时平均自然 O(3)混合比的贡献高达 25-30 ppbV（或高达 50%）。模拟野火排放物在西部的几个地点使 8 小时自然 O(3)增加了 50 ppbV（在某些情况下超过 90%）。模拟还表明，自然排放（包括生物源、海洋源、地质源和火灾）对美国东部三分之二地区和美国西部大部分地区的年平均总细颗粒物质量的贡献≤40%。生物源排放是整个美国地区颗粒物质的主要来源，而野火排放是次要来源。在整个模拟域的平均值中，背景和自然臭氧占主导地位，人为源产生的臭氧仅在夏季对总臭氧的贡献达到三分之一。相比之下，背景对细颗粒物水平的贡献相对较小。模型结果还与美国环境保护署（EPA）用于区域霾法规决策的自然光散射颗粒浓度的默认值进行了对比。模型不支持 EPA 指导方针中的区域差异，并且 EPA 对默认值的不确定性估计远小于自然颗粒浓度的模型变异性。
