Clean Air Markets
EPA's Clean Air Markets Programs address several environmental issues which are briefly described below with links to more information.
Acid deposition, or acid rain as it is commonly known, occurs when emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) react in the atmosphere with water, oxygen, and oxidants to form various acidic compounds. Prevailing winds can transport these compounds hundreds of miles, across state lines and national borders. These compounds then fall to the earth in either dry form (such as gas and particles) or wet form (such as rain, snow, and fog). Visit EPA's Acid Rain website for more information.
Over the past century, human activities have released large amounts of carbon dioxide and other greenhouse gases into the atmosphere. The majority of greenhouse gases come from burning fossil fuels to produce energy, although deforestation, industrial processes, and some agricultural practices also emit gases into the atmosphere. Visit EPA’s Climate Change: Basic Information page for more information on the causes of climate change and what you can do to make a difference.
Ground-Level Ozone (Smog)
Ground-level ozone, or smog, is air pollution that makes breathing more difficult, negatively effects health and ecosystems, and impairs visibility. Ground-level ozone is created when NOx reacts with other chemicals in the air, especially in the presence of strong sunlight. NOx can travel long distances before reacting to form ozone, creating regional problems instead of only affecting the local area where it is emitted. Visit EPA's Ozone Pollution website for more information.
Regional Haze and Visibility
Regional haze is the visibility impairment that occurs when particles and gases in the atmosphere, including sulfates and nitrates, scatter and absorb light. The pollutants that are associated with acid rain are the same ones that reduce visibility. Visibility tends to vary by season and geography because it is also affected by the angle of the sunlight and the level of humidity. High relative humidity heightens pollution's effects on visibility because particles such as sulfates accumulate water and grow to a size at which they scatter more light, thus creating haze. Visit EPA's Visibility website for more information.
Mercury is a naturally occurring element that can be found throughout the environment. Human activities, such as burning coal and using mercury to manufacture certain products, have increased the amount of mercury in many parts of the environment including the atmosphere, lakes, and streams. Once mercury from the air reaches water, microorganisms can change it into methylmercury, a highly toxic form that builds up in fish. People are primarily exposed to mercury by eating contaminated fish. Methylmercury exposure is a particular concern for women of childbearing age, unborn babies, and young children, because studies have linked high levels of methylmercury to damage to the developing nervous system. This damage can impair children’s ability to think and learn. EPA’s Mercury and Air Toxics Standards (MATS) limit the emissions of mercury and other toxics from power plants.