In 1970, Congress passed the Clean Air Act Extension, directing the newly formed Environmental Protection Agency to develop national standards for six airborne pollutants, including carbon monoxide, fine particulate matter, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. Under these National Ambient Air Quality Standards (NAAQS), the EPA monitors levels for each of the six pollutants named above, usually on a county-by-county basis, although the EPA can also combine counties into larger areas. The EPA must use “the latest scientific knowledge” to set the standards so that the public welfare, economic value, and personal comfort are protected.