Another defining characteristic about Europe’s pollution is that it is relatively confined to certain areas. In fact, while the overall pollution is worse than in the United States, northern Europe (Scandinavia and the Baltic States) has the same average pollution level as our nation. Western Europe (Germany and west) jumps up to about 16, and the eastern and Mediterranean regions are around 26 micrograms per cubic meter. Turkey has particularly high pollution levels and relatively low levels of income by European standards. With Turkey taken out of the picture, Europe’s average drops to 18.7.

Why do the United States and European maps look different? Part of the answer may just be a question of timing, but the differences also reflect choices. It wasn’t that long ago when many American cities were heavily polluted; Los Angeles was known as the smog capital of the world, and white-collar workers in Gary, Ind., would bring two shirts to work to ensure they always had a clean white one to get them through the day. But from 1970, when the Clean Air Act was passed, to today, there has been a substantial improvement in air quality, with much of it because of state and federal regulations. That change didn’t happen overnight or by accident.

When one compares pollution readings from around the globe, it is evident that lower-income countries tend to have higher pollution. However, this is not a law of nature. Pollution reflects societal choices about incurring costs in exchange for health and other benefits that are embodied in policies like the Clean Air Act. Since its passage almost 45 year ago, we have learned much about the health benefits of cleaner air and ways to clean the air inexpensively.

In the coming years, China and India have an opportunity to take advantage of these lessons in the name of improving their citizens’ health. Because their actions to reduce particulates air pollution can lead to cuts in greenhouse gas emissions, it may also reduce the risk of disruptive climate change for the world.