Program - A vehicle inspection program that is required for a polluted area. Periodic inspections, usually done once a year or once every two years, check to see that a vehicle is being maintained to keep pollution down and that emission control systems are working properly. Vehicles that do not pass inspection must be repaired. Mobile Source - A moving object that emits pollutants. Nitrogen oxides are produced from burning fuels, including gasoline and coal.
Nitrogen oxides are also a precursor pollutant that contributes to the formation of acid rain.
In the presence of sunlight and heat, gaseous air pollutants react to produce ground-level ozone smog. These pollutants have many sources including automobiles, trucks, buses and industrial smokestacks. Ground-level ozone, however, is the main contributor to urban smog. Ozone Action Day - In 2000, Ozone Action day was discontinued. In previous years, these announcements were made when forecasted weather conditions made it likely that an ozone exceedance would occur on the following day.