Smog over Mexico City (IMAGE) American Geophysical Union Caption In the lower atmosphere, sunlight reacts with nitrogen oxides, methane and other volatile organic molecules to produce ozone. At this level of the atmosphere, ozone acts as a pollutant, rather than a protectant, as shown in this aerial photo of Mexico City. New research shows that if emission rates continue unchecked, some regions of the United States could experience between three and nine additional days per year of unhealthy ozone levels by 2050. Credit Credit: Fidel Gonzalez via Wikimedia Commons. <a href="https://commons.wikimedia.org/wiki/File:AerialViewMexicoCity.jpg" target="_blank">https://commons.wikimedia.org/wiki/File:AerialViewMexicoCity.jpg</a> Usage Restrictions See <a href="https://commons.wikimedia.org/wiki/File:AerialViewMexicoCity.jpg" target="_blank">https://commons.wikimedia.org/wiki/File:AerialViewMexicoCity.jpg</a> License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.