Smog is up 65 percent in the western U.S., according to a new study. Researchers say it's because of Asian countries' emission levels of nitrogen oxides, which have tripled since 1990. The findings come from pollution data collected in cities and national parks across the western U.S. The Asian-made gases travel across the ocean. They've offset the 50 percent cut in emissions of nitrogen oxides made by the U.S. over the past 25 years.
Class discussion: How important are international agreements to cleaning up our air and water? Has U.S. air or water pollution ever caused problems for another nation? How do pollution problems in one state impact other states? What causes acid rain and what problems does it cause? How is fertilizer and animal waste linked to “dead zones” in oceans and lakes? Can you find examples of pollution spreading past state and national borders?