What are the human health and welfare effects of these pollutants?
The engines that are covered by this proposal contribute to ozone formation and ambient PM and CO levels. These pollutants are subject to our National Ambient Air Quality Standards (NAAQS), and states that exceed NAAQS levels are required to take measures to reduce emissions. In addition, these engines also emit Mobile Source Air Toxics. • Ozone. Ground-level ozone, the main ingredient in smog, is formed by complex chemical reactions of volatile organic compounds (VOC) and NOx in the presence of heat and sunlight. Ozone forms readily in the lower atmosphere, usually during hot summer weather. Volatile organic compounds are emitted from a variety of sources, including motor vehicles, chemical plants, refineries, factories, consumer and commercial products, and other industrial sources. Volatile organic compounds also are emitted by natural sources such as vegetation. Oxides of nitrogen are emitted largely from motor vehicles, off-highway equipment, power plants, and other sources of com
