In a draft report released Thursday, the U.S. EPA said smog levels could increase significantly in many areas of the United States due to climate change, especially in the Northeast, lower Midwest, and mid-Atlantic regions. Smog is mainly a summer phenomenon in most places, caused by sunlight reacting with nitrogen oxides and volatile organic compounds. However, climate change could expand the smog season into spring and fall as well. Climate change could cause more smoggy days and increased smog levels by prompting plants to release more VOCs and by increasing the frequency of lightning storms, which are natural sources of nitrogen oxides. “These findings also indicate, that, where climate-change-induced increases in [smog] do occur, damaging effects on ecosystems, agriculture, and health will be especially pronounced, due to increases in the frequency of extreme pollution events,” the analysis said.