洛杉矶的姐妹城市墨西哥城（Mexico City）和印度孟买（Mumbai）也面临类似的挑战。洛杉矶和墨西哥城的地形都让废气不容易散发，这三个城市都是人口数以千万计的“大”都市。私人、公共和商业运输需要大量的汽车，飞机、火车和港口船舶的排放也加重了污染。

有着类似空气质量问题的地区自然成了寻求解决方案的合作者。印度-美国加州空气污染治理项目（India-California Air Pollution Mitigation Program）是由印度的能源与资源研究所（TERI- The Energy and Resources Institute India）和美国加州大学圣地亚哥分校（University of California at San Diego）以及加州空气资源委员会（California Air Resources Board）于2014年合作的一个研究项目。该研究发现，促使洛杉矶显着改善空气质量的技术和燃料可以在印度复制，有助于立刻改善健康、食物和水的的质量。

该研究报告指出“加州的实践已经证明，可以在不减缓经济增长的情况下大大降低 污染。”

监管与创新

第二次世界大战后，空气污染成了洛杉矶的一个难题。有效的补救措施需要时间，也需要政府、企业和居民之间的合作。上世纪70年代，洛杉矶通过 《清洁空气法》（Clean Air Act）等 联邦法律以及国家汽车排放标准，再加上加州本身严格的监管措施，开始向污染宣战。

但雾霾仍然挥之不去。后来 通过安装催化转换器减少汽车尾气排放，才真正改善了空气质量。

最近由南加州大学（USC- University of Southern California）进行的一项研究显示，洛杉矶居民比20年前更健康了，这要归功于空气中二氧化氮和颗粒物的显着下降。该研究报告的作者说，他们的研究成果证实了，社会各界为 改善整体空气质量共同努力有益于公共健康水平获得实质性的重大 改善。

远大目标

像世界上其他城市一样，洛杉矶也必须为保持健康的空气质量加倍努力。随着人口增长，汽车和其他污染源的数量也在增长。

通过立法、创新和节能等方式 抗击空气污染和气候变化是洛杉矶市长埃里克·贾塞提（Eric Garcetti）的一桩头等大事，他是C40指导委员会（C40 Steering Committee）和奥巴马总统的气候工作组（President Obama’s Climate Task Force）成员。C40是各国城市为解决城市环境问题建立的市长国际网络。

洛杉矶于今年4月推出具有胆略 的可持续城市计划（Sustainable Cities Plan）。

为空气质量制定的高标准包括，把对健康有害的空气污染天数从2013年记录的40天下降到2025年的零，并通过替代燃料的使用和可持续性发电，大幅减少污染物的排放。

保护能捕集二氧化碳的公园和周围的森林是另一项策略。洛杉矶河（ Los Angeles River）的一个河段以及毗邻的绿地即将恢复绿化。过去六十年，河岸上铺满了用于控制洪水和径流的混凝土。

这一切都意味着公民会更加健康。正如南加州大学研究报告首席作者W.詹姆斯·高德曼（W. James Gauderman）对《南加州大学新闻》（USC News）所说的那样，“我们希望我们的研究成果对南加州以外的地区也适用，因为和改善健康关系最为密切的污染物——二氧化氮和颗粒—— 在任何都市环境中都在上升。”

Once smog-shrouded, LA has improved its air quality

Los Angeles, or LA, may be among the U.S. cities with the dirtiest air, but it’s breathing much more easily than it did a few decades ago, when cars, refineries and backyard incinerators spewed greenhouse gases and particulate matter unchecked. Technology and today’s strict controls on automobile and industrial emissions accomplished this change.

LA’s sister cities, Mexico City and Mumbai, India, face similar challenges. Los Angeles and Mexico City both have geography that traps emissions, and all three cities have populations numbering in the tens of millions in their “greater” metropolitan areas. Motor vehicles are used for private, public and commercial transport, with added pollution from planes, trains and — in the port cities — ships.

Localities with similar air quality problems are natural collaborators on solutions. A 2014 study by the India-California Air Pollution Mitigation Program, a joint initiative of The Energy and Resources Institute (TERI) India, the University of California at San Diego and the California Air Resources Board, finds that technologies and fuels that have dramatically improved air quality in LA could be implemented in India and immediately improve health as well as food and water supplies.

“California has demonstrated that these pollutants can be mitigated drastically without slowing down economic development,” the report says.

Regulation and innovation

Air pollution became a problem in Los Angeles after World War II. Effective remedies took time and required coordination of government, businesses and residents. Federal laws, such as the Clean Air Act, and national emissions standards for cars, plus California’s own strict regulatory measures, kick-started antipollution efforts during the 1970s.

But smog continued to hang in the air. Real progress came after the adoption of catalytic converters to cut vehicle emissions.

A recent University of Southern California (USC) study shows that LA residents are healthier than they were 20 years ago, thanks to dramatic declines in nitrogen dioxide and particulate matter. The study’s authors say their findings support a correlation between “broad-based efforts to improve general air quality” and “substantial and measurable public health benefits.”

Ambitious goals

Like other cities around the world, LA must redouble efforts to maintain healthy air. As population grows, the number of vehicles and other pollution sources grows too.

Tackling air pollution and climate change through legislation, innovation and conservation is a priority for LA Mayor Eric Garcetti, who serves on the C40 Steering Committee andPresident Obama’s Climate Task Force.  The C40 is an international network of mayors working to solve urban environmental problems.

Strategies in LA’s Sustainable Cities Plan, launched in April, are bold.

Ambitious air quality targets include cutting unhealthy air pollution days from 40 recorded in 2013 to none in 2025, and a drastic decrease in polluting emissions through alternative fuel use and sustainable power generation.

Conserving parks and surrounding forests, which store carbon dioxide, is another strategy. A stretch of the Los Angeles River and adjoining green spaces will be restored after six decades during which the river has been a concrete sluice for flood control and runoff.

All this means healthier citizens, and as lead USC study author W. James Gauderman told USC News, “We expect that our results are relevant for areas outside Southern California, since the pollutants we found most strongly linked to improved health — nitrogen dioxide and particulate matter — are elevated in any urban environment.”