Significant reductions in emissions of SO₂, NO_x, volatile organic compounds (VOCs), and primary particulate matter (PM) took place in the US from 1990 to 2010. We evaluate here our understanding of the links between these emissions changes and corresponding changes in concentrations and health outcomes using a chemical transport model, the Particulate Matter Comprehensive Air Quality Model with Extensions (PMCAMx), for 1990, 2001, and 2010. The use of the Particle Source Apportionment Algorithm (PSAT) allows us to link the concentration reductions to the sources of the corresponding primary and secondary PM. The reductions in SO₂ emissions (64 %, mainly from electric-generating units) during these 20 years have dominated the reductions in PM_2.5, leading to a 45 % reduction in sulfate levels. The predicted sulfate reductions are in excellent agreement with the available measurements. Also, the reductions in elemental carbon (EC) emissions (mainly from transportation) have led to a 30 % reduction in EC concentrations. The most important source of organic aerosol (OA) through the years according to PMCAMx is biomass burning, followed by biogenic secondary organic aerosol (SOA). OA from on-road transport has been reduced by more than a factor of 3. On the other hand, changes in biomass burning OA and biogenic SOA have been modest. In 1990, about half of the US population was exposed to annual average PM_2.5 concentrations above 20 µg m⁻³, but by 2010 this fraction had dropped to practically zero. The predicted changes in concentrations are evaluated against the observed changes for 1990, 2001, and 2010 in order to understand whether the model represents reasonably well the corresponding processes caused by the changes in emissions.

中文翻译：

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1990-2010年美国PM2.5浓度变化及其来源

从 1990 年到 2010 年，美国的 SO ₂、NO _x、挥发性有机化合物 (VOC) 和初级颗粒物 (PM) 的排放量显着减少。我们在此评估我们对这些排放量变化与相应变化之间联系的理解1990 年、2001 年和 2010 年使用化学传输模型、带扩展的微粒物质综合空气质量模型 (PMCAMx) 的浓度和健康结果。粒子源分配算法 (PSAT) 的使用使我们能够将浓度降低联系起来到相应的初级和次级 PM 的来源。这 20 年中 SO ₂排放量的减少（64%，主要来自发电机组）主导了 PM _2.5的减少，导致硫酸盐水平降低 45%。预测的硫酸盐还原与可用的测量结果非常一致。此外，元素碳 (EC) 排放量（主要来自运输）的减少导致 EC 浓度降低了 30%。根据 PMCAMx，多年来有机气溶胶 (OA) 的最重要来源是生物质燃烧，其次是生物二次有机气溶胶 (SOA)。来自公路运输的 OA 减少了 3 倍以上。另一方面，生物质燃烧 OA 和生物 SOA 的变化不大。1990 年，大约一半的美国人口暴露于年平均 PM _2.5浓度超过 20  µg m ^{-3 的环境中}，但到 2010 年，这一比例几乎降至零。对照 1990 年、2001 年和 2010 年观测到的变化评估浓度的预测变化，以了解该模型是否合理地代表了由排放变化引起的相应过程。