美中法合作研究发现：车辆排放减少，死亡人数减少

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Urban emissions Credit: Pixabay/CC0 Public Domain

据物理学家组织网（Phys.org）2021年12月18日报道，研究结果显示，车辆排放的减少，减少了死亡人数（Vehicle emission declines decreased deaths, study finds）。研究人员表示，由于最近汽车排放的减少，美国成千上万人的生命和数千亿美元得到了拯救。

哈佛大学（Harvard University）研究环境和公共健康的研究人员与中国和法国的研究人员合作，研究了十多年来汽车排放量下降的影响。他们发现，死亡人数从2008年的27700人下降到2017年的19800人，减少排放带来的经济效益总计2700亿美元。相关研究结果于2021年12月15日周三已经在《美国国家科学院院刊》(Proceedings of the National Academy of Sciences)杂志网站发表——Ernani F. Choma, John S. Evans, José A. Gómez-Ibáñez, Qian Di, Joel D. Schwartz,James K. Hammitt, John D. Spengler. Health benefits of decreases in on-road transportation emissions in the United States from 2008 to 2017. Proceedings of the National Academy of Sciences, December 21, 2021, 118 (51): e2107402118. DOI: 10.1073/pnas.2107402118. https://doi.org/10.1073/pnas.2107402118. 参与此项研究的除了美国哈佛大学之外，还有来自中国清华大学（Tsinghua University, Beijing 100084, China）和法国图卢兹卡皮托尔大学（Université Toulouse Capitole, 31080 Toulouse, France）的研究人员。

在此项研究中，研究人员还得出结论，如果汽车在这段时间内继续排放2008年水平的空气污染（air pollution ），2017年的死亡总数将是2008年的2.4倍。该研究指出，由于对化石燃料公司和汽车制造商实施了更严格的监管，减轻了人们的健康负担，而小汽车、皮卡（pickup trucks）和运动型多用途汽车 (sport utility vehicle简称SUV)等轻型车辆占了很大一部分。但研究人员发现，这些好处受到人口增长和老龄化以及司机购买更大的汽车和驾驶更多车辆的限制。

哈佛大学环境健康研究者、该研究的第一作者埃尔纳尼·乔马(Ernani Choma)说：“尽管在减少排放方面取得了实质性进展，但人口和更大的车辆会产生抵消效应。所以，如果我们不制定更严格的政策，就很难取得实质性进展（ substantial progress）。”

虽然之前已有关于减排的健康效益和经济影响的研究，但据不属于该研究小组的专家说，这项研究描绘了排放如何影响公众健康（public health）的更精确的画面。美国明尼苏达大学(University of Minnesota)专门从事空气质量研究的苏米尔·塔克拉(Sumil Thakrar)说：“在过去10年里，良好的环境政策大幅减少了交通排放。但要很好地理解这些排放控制的好处是困难的，因为它需要跟踪许多其他活动部件。我认为作者们做得很好。”

该研究还考察了减少汽车空气污染对气候的好处，但发现这些好处只占总体经济收益的3%至19%。美国乔治华盛顿大学(George Washington University)环境与职业健康及全球健康副教授苏珊·安内伯格(Susan Anenberg)说，这是因为美国大多数减少交通运输排放的方法都是针对遏制空气污染，而不是气候变化（climate change）。她说:“催化转换器、柴油微粒过滤器等能够捕获向环境排出的污染物，但对(二氧化碳)没有任何作用。”

这也是埃尔纳尼·乔马和他的同事们建议采取更严格的政策来控制排放的原因之一。他说，另一个原因是，如果人口和车辆大小以及使用的上升趋势继续下去，那么在未来创造研究中强调的健康益处的相同政策将不再有效。他说，“如果我们展望2030年，什么都没有改变，你只会看到汽车尾气造成的死亡人数略有下降。这就是更严格政策的情况。”

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Decreased vehicle emissions linked with significant drop in deaths attributable to air pollution

Significance

Despite decades of reductions in vehicle emissions in the United States, their impacts remain large, and the offsetting effects of different factors on benefits achieved in recent years are not well understood. We assess benefits from 2008 to 2017 on a fine spatial resolution using the latest epidemiological evidence and emissions inventories. We find that regulation continues to yield large benefits: $270 (190 to 480) billion in 2017 from reduced PM_2.5-attributable mortality and greenhouse gas emissions. Traffic-related PM_2.5-attributable mortality would have been 2.4 times as large in 2017 if vehicles had still been emitting at 2008 levels, accounting for most benefits. Urban passenger light-duty vehicles have become increasingly important, and major health gains require more stringent policies to curb their emissions.

Abstract

Decades of air pollution regulation have yielded enormous benefits in the United States, but vehicle emissions remain a climate and public health issue. Studies have quantified the vehicle-related fine particulate matter (PM_2.5)-attributable mortality but lack the combination of proper counterfactual scenarios, latest epidemiological evidence, and detailed spatial resolution; all needed to assess the benefits of recent emission reductions. We use this combination to assess PM2.5-attributable health benefits and also assess the climate benefits of on-road emission reductions between 2008 and 2017. We estimate total benefits of $270 (190 to 480) billion in 2017. Vehicle-related PM_2.5-attributable deaths decreased from 27,700 in 2008 to 19,800 in 2017; however, had per-mile emission factors remained at 2008 levels, 48,200 deaths would have occurred in 2017. The 74% increase from 27,700 to 48,200 PM_2.5-attributable deaths with the same emission factors is due to lower baseline PM_2.5 concentrations (+26%), more vehicle miles and fleet composition changes (+22%), higher baseline mortality (+13%), and interactions among these (+12%). Climate benefits were small (3 to 19% of the total). The percent reductions in emissions and PM_2.5-attributable deaths were similar despite an opportunity to achieve disproportionately large health benefits by reducing high-impact emissions of passenger light-duty vehicles in urban areas. Increasingly large vehicles and an aging population, increasing mortality, suggest large health benefits in urban areas require more stringent policies. Local policies can be effective because high-impact primary PM_2.5 and NH₃ emissions disperse little outside metropolitan areas. Complementary national-level policies for NO_x are merited because of its substantial impacts—with little spatial variability—and dispersion across states and metropolitan areas.