The report was based on data collected between 2010 and 2012 and found that smog had worsened in 22 of the US’s 25 largest cities.

Los Angeles, Houston, Washington, Baltimore, New York City and Chicago were some of the worst affected.

Global warming was cited as a factor which worsened the smog that surrounds the cities.

"Weather played a factor," the report said.

"The warmer summers in 2010 and 2012 contributed to higher ozone readings and more frequent ozone days. Sunlight and heat create conditions that increase the risk of high ozone levels."

The report's release comes a day after the Supreme Court endorsed the Environmental Protection Agency's efforts to deal with smog and soot that travel across state lines.

The ALA has also been pushing to tighten air pollution standards, and has supported the EPA's moves to force power plants to cut carbon dioxide emissions.

A growing body of research over the past decade has connected air pollution to increased deaths from heart disease and respiratory illnesses. The World Health Organisation said last autumn that particulate pollution caused lung cancer.

Eighteen of the 25 US cities with the worst particulate pollution saw a drop in year-round pollutants because of cuts in emissions for coal-fired power plants and other measures.

But the report said those cities still failed to meet national standards for year-round particle pollution.