Air pollution from fine particulate matter (PM_2.5) is increasingly driving the global burden of disease (1), and diesel-powered vehicles are substantial contributors. Recognizing the public health impacts of diesel PM_2.5 (DPM) (2), many countries have reduced emissions of DPM from both on- and off-road mobile sources over the past three decades. The previous US federal administration, however, changed course by eliminating or weakening policies and standards that govern these emissions. In contrast, the State of California has continued to reduce mobile-source DPM emissions using the state's long-standing authority under the Clean Air Act (CAA) to regulate air pollution more stringently than the federal government. Our analysis of mobile-source DPM emissions suggests that many California sector-based policies have been highly effective relative to the rest of the US. To improve health in communities disproportionately affected by these emissions, we point to opportunities to further reduce DPM emissions in California, in the US more broadly, and in parts of the world where countries have less aggressive vehicle emissions policies than the US (3).

细颗粒物（PM _2.5）造成的空气污染正日益推动全球疾病负担（1），而柴油动力汽车是其中的主要贡献者。认识到PM _2.5（DPM）柴油对公共健康的影响（2），在过去的三十年中，许多国家/地区减少了公路和越野移动源的DPM排放。但是，先前的美国联邦政府通过取消或削弱管理这些排放的政策和标准来改变了发展方向。相比之下，加利福尼亚州利用其长期以来根据《清洁空气法》（CAA）所拥有的权力来减少移动源DPM排放，以比联邦政府更严格地管制空气污染。我们对移动源DPM排放的分析表明，相对于美国其他地区，许多基于加利福尼亚行业的政策都非常有效。为了改善受这些排放影响最大的社区的健康状况，我们指出了进一步降低美国加利福尼亚州DPM排放的机会，3）。