Wilkins Joseph L, Pouliot George, Foley Kristen, Appel Wyat, Pierce Thomas
US Environmental Protection Agency, Computational Exposure Division, National Exposure Research Laboratory, Research Triangle Park, NC 27711, USA.
Int J Wildland Fire. 2018;27(10). doi: 10.1071/wf18053.
Wildland fire emissions are routinely estimated in the US Environmental Protection Agency's National Emissions Inventory, specifically for fine particulate matter (PM) and precursors to ozone (O); however, there is a large amount of uncertainty in this sector. We employ a brute-force zero-out sensitivity method to estimate the impact of wildland fire emissions on air quality across the contiguous US using the Community Multiscale Air Quality (CMAQ) modelling system. These simulations are designed to assess the importance of wildland fire emissions on CMAQ model performance and are not intended for regulatory assessments. CMAQ ver. 5.0.1 estimated that fires contributed 11% to the mean PM and less than 1% to the mean O concentrations during 2008-2012. Adding fires to CMAQ increases the number of 'grid-cell days' with PM above 35 μg m by a factor of 4 and the number of grid-cell days with maximum daily 8-h average O above 70 ppb by 14%. Although CMAQ simulations of specific fires have improved with the latest model version (e.g. for the 2008 California wildfire episode, the correlation = 0.82 with CMAQ ver. 5.0.1 = 0.68 for CMAQ ver. 4.7.1), the model still exhibits a low bias at higher observed concentrations and a high bias at lower observed concentrations. Given the large impact of wildland fire emissions on simulated concentrations of elevated PM and O, improvements are recommended on how these emissions are characterised and distributed vertically in the model.
美国环境保护局的国家排放清单通常会对野火排放进行估算，特别是针对细颗粒物（PM）和臭氧（O）的前体物；然而，该领域存在大量不确定性。我们采用强力归零敏感性方法，使用社区多尺度空气质量（CMAQ）建模系统来估算美国本土野火排放对空气质量的影响。这些模拟旨在评估野火排放在CMAQ模型性能方面的重要性，并非用于监管评估。CMAQ 5.0.1版本估计，在2008 - 2012年期间，火灾对平均PM浓度的贡献为11%，对平均O浓度的贡献小于1%。将火灾排放纳入CMAQ后，PM浓度高于35 μg/m³的“网格单元天数”增加了4倍，日最大8小时平均O浓度高于70 ppb的网格单元天数增加了14%。尽管使用最新模型版本对特定火灾的CMAQ模拟有所改进（例如，对于2008年加利福尼亚野火事件，CMAQ 5.0.1版本的相关性为0.82，CMAQ 4.7.1版本的相关性为0.68），但该模型在观测浓度较高时仍表现出低偏差，在观测浓度较低时表现出高偏差。鉴于野火排放对模拟的高浓度PM和O浓度有很大影响，建议在模型中对这些排放的特征描述和垂直分布方式进行改进。
