Using observations and model simulations (ESM4.1) during 1988–2018, we show large year‐to‐year variability in western U.S. PM_2.5 pollution caused by regional and distant fires. Widespread wildfires, combined with stagnation, caused summer PM_2.5 pollution in 2017 and 2018 to exceed 2 standard deviations over long‐term averages. ESM4.1 with a fire emission inventory constrained by satellite‐derived fire radiative energy and aerosol optical depth captures the observed surface PM_2.5 means and extremes above the 35 μg/m³ U.S. air quality standard. However, aerosol emissions from the widely used Global Fire Emissions Database (GFED) must be increased by 5 times for ESM4.1 to match observations. On days when observed PM_2.5 reached 35–175 μg/m³, wildfire emissions can explain 90% of total PM_2.5, with smoke transported from Canada contributing 25–50% in northern states, according to model sensitivity simulations. Fire emission uncertainties pose challenges to accurately assessing the impacts of fire smoke on air quality, radiation, and climate.

中文翻译：

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2017-2018年美国西部山火造成的夏季PM2.5污染极端事件

使用1988-2018年期间的观测资料和模型模拟（ESM4.1），我们显示了由区域性火灾和远距离火灾引起的美国西部PM _2.5污染年际差异很大。广泛的野火加上停滞，导致2017年和2018年夏季PM _2.5污染超过长期平均值的2个标准差。ESM4.1具有受卫星衍生的火辐射能量和气溶胶光学深度限制的火源清单，可捕获的观测表面PM _2.5平均值和高于美国35 g / m ³空气质量标准的极端值。但是，为了使ESM4.1与观测值相匹配，必须将广泛使用的全球火灾排放数据库（GFED）中的气溶胶排放量增加5倍。在观察到PM _2.5的日子根据模型敏感性模拟，野火排放量达到35–175μg/ m ^3时，可解释90％的PM _2.5，而从加拿大运来的烟在北部各州的贡献为25–50％。火灾排放的不确定性给准确评估火灾烟雾对空气质量，辐射和气候的影响提出了挑战。