In the 1950s, Los Angeles held massive protests against the dirty air in the city. Smog over U. S. cities was mainly attributed to vehicle emissions and intensified over the following decades, until the United States Environmental Protection Agency (USEPA) was created in 1970 and the U. S. Clean Air Act was passed, which was subsequently revised several times and refined. As a result of these actions, air quality has improved significantly since the 1970s and 1980s.
However, according to new research published in the American journal Proceedings of the National Academy of Sciences, the reduction of one of the main components of smog, nitric oxide, slowed significantly between 2011 and 2015. However, the reason for this slowdown remains unclear.
High concentrations of nitrogen oxides in the air, which when exposed to sunlight, create smog, declined about 75% more slowly in 2011–2015 than in 2005–2009.
According to a new study by the American Lung Association, many Americans are still exposed to too much smog. Among the leaders in the most polluted regions of the United States are the metropolitan area of New York and New Jersey, as well as 8 cities in California. The life expectancy of millions of people in these cities is being reduced by poor air quality, which spoils their health in two ways.
One of the downsides is damage to the lungs and difficulty breathing. The second is heart problems, which are caused by small particles in car exhaust, which cause hardening of the walls of the heart arteries.
Helen Warden, a scientist at the National Center for Atmospheric Research, says even satellite imagery showing nitrogen oxide levels in 2005-2009. and 2011–2015 look completely different.
Initially, Warden and her team believed that emissions from China that reached the shores of the United States were to blame, but "this was not confirmed by the data," as in this case, more nitrogen oxide emissions would be observed off the West Coast of the United States, rather than the East. That is, this means that the reason must be sought within the country itself.
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On the one hand, it is possible that cars are to blame, especially sports cars, which are still very popular. On the other hand, today, thanks to the advent of a catalytic converter of exhaust gases, the emissions from cars have decreased significantly.
Another possible reason is industry. In 2007, an economic recession came, many production stopped, which means that air emissions have decreased. In 2011, an economic recovery began, and production was again in full swing.
In any case, further research will be required to pinpoint the cause. With Trump's rise to power, this becomes more difficult, as his administration has proposed introducing standards of "transparency" in such studies, which seems almost impossible, since they contain personal data of patients that cannot be published.
Overall, while US air quality has improved significantly over the past decades and continues to do so, the problem is still far from being resolved. And even if smog has apparently decreased, this does not mean that it has ceased to cause harm to human health.