The Clean Air Act and 1990 Amendments stipulate that EPA must determine and report annually the quality of the nation's air. Proposed changes and actual changes are recorded in the Federal Register. The EPA web site maintains excellent access to this history of proposals and changes.
Particulates are mixtures of solid and liquid droplets of material that vary in size and origin.
Particulates of this size are referred to as PM-10 particles. Measured and reported by air pollution monitors or samplers , PM-10 particles in urban environments are often composed of soot, acid condensates, and sulfate and nitrate particles. High temperature combustion of fossil fuels in motor vehicles is the primary source of nitrogen oxides in outdoor air. Nitrogen oxides are relatively insoluble in water. Ozone, may form in the lower atmosphere as a result of nitrogen dioxide pollution.