The National Ambient Air Quality Standards （NAAQS） are standards established by the United States Environmental Protection Agency that apply for outdoor air throughout the country. Primary standards are designed to protect human health, with an adequate margin of safety, including sensitive populations such as children, the elderly, and individuals suffering from respiratory disease. Secondary standards are designed to protect public welfare from any known or anticipated adverse effects of a pollutant（e.g. building facades, visibility, crops, and domestic animals）. NAAQS requires the EPA to set standards on six criteria air contaminants: Ozone （O3） Particulate Matter PM10, coarse particles: 2.5 micrometers （μm） to 10 μm in size （although current implementation includes all particles 10 μg or less in the standard） PM2.5, fine particles: 2.5 μm in size or less Carbon monoxide （CO） Sulfur dioxide （SO2） Nitrogen oxides （NOx） Lead （Pb）