Li Chi, Martin Randall V, van Donkelaar Aaron
Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States.
ACS EST Air. 2024 May 9;1(7):637-645. doi: 10.1021/acsestair.4c00004. eCollection 2024 Jul 12.
Motivated by the recent tightening of the US annual standard of fine particulate matter (PM) concentrations from 12 to 9 μg/m, there is a need to understand the spatial variation and drivers of historical PM reductions. We evaluate and interpret the variability of PM reductions across the contiguous US using high-resolution estimates of PM and its chemical composition over 1998-2019, inferred from satellite observations, air quality modeling, and ground-based measurements. We separated the 3092 counties into four characteristic regions sorted by PM trends. Region 1 (primarily Central Atlantic states, 25.9% population) exhibits the strongest population-weighted annual PM reduction (-3.6 ± 0.4%/yr) versus Region 2 (primarily rest of the eastern US, -3.0 ± 0.3%/yr, 39.7% population), Region 3 (primarily western Midwest, -1.9 ± 0.3%/yr, 25.6% population), and Region 4 (primarily the Mountain West, -0.4 ± 0.5%/yr, 8.9% population). Decomposition of these changes by chemical composition elucidates that sulfate exhibits the fastest reductions among all components in 2720 counties (76% of population), mostly over Regions 1-3, with the 1998-2019 mean sulfate mass fraction in PM decreasing from Region 1 (29.5%) to Region 4 (11.8%). Complete elimination of the remaining sulfate may be insufficient to meet the new standard for many regions in exceedance. Additional measures are needed to reduce other PM sources and components for further progress.
受美国近期将细颗粒物（PM）年度标准浓度从12微克/立方米收紧至9微克/立方米的推动，有必要了解历史PM减排的空间变化及其驱动因素。我们利用1998 - 2019年期间从卫星观测、空气质量模型和地面测量推断出的PM及其化学成分的高分辨率估计值，评估并解释了美国本土PM减排的变异性。我们将3092个县按PM趋势分为四个特征区域。区域1（主要是中大西洋各州，占人口的25.9%）的人口加权年度PM减排最强（-3.6±0.4%/年），而区域2（主要是美国东部其他地区，-3.0±0.3%/年，占人口的39.7%）、区域3（主要是中西部西部，-1.9±0.3%/年，占人口的25.6%）和区域4（主要是美国西部山区，-0.4±0.5%/年，占人口的8.9%）。按化学成分对这些变化进行分解表明，在2720个县（占人口的76%）中，硫酸盐在所有成分中减排最快，主要分布在区域1至3，1998 - 2019年PM中硫酸盐质量分数的平均值从区域1（29.5%）降至区域4（11.8%）。对于许多超标地区来说，完全消除剩余的硫酸盐可能不足以达到新标准。需要采取额外措施来减少其他PM来源和成分，以取得进一步进展。
