Ozone is a highly reactive gas that is a form of oxygen.
It is the main component of the air pollution known as smog. Hydrocarbons are emitted by motor vehicles, oil and chemical storage and handling facilities, and a variety of commercial and industrial sources such as gas stations, dry cleaners and degreasing operations. Oxides of nitrogen are a by-product of burning fuel in sources such as power plants, steel mills and other heavy industry and in motor vehicles. Wind can carry NOx hundreds of miles, so people who don t live in areas with high levels of NOx emissions aren t necessarily safe from these emissions. EPA has been tracking NOx and five other major air pollutants since 1970, and found that while carbon monoxide, lead, particulate matter, sulfur dioxide, and volatile organic compounds have decreased significantly, NOx emissions have increased approximately 10 percent.