1971 Minor Air Pollutants Pollutants other than fluorides, ozone, PAN, and sulfur dioxide are considered to be minor pollutants. Common Sources Oxides of nitrogen are formed by combustion at high temperatures in the presence of two natural components of the air, nitrogen and oxygen.
Automotive exhaust is probably the largest producer of NOx.
Other sources include petroleum refining, combustion of fuel used in heat and power generating, burning of organic wastes, and the manufacturing of nitric acid, paint, roofing, rubber, soap, and nylon. Ethylene comes from the manufacture of illuminating gas, automobile exhaust, combustion of various fuels or any organic substance, petroleum refining, and manufacturing of polyethylene. Ammonia injury to plants and plant products has often been caused by refrigeration gas escaping in cold storage rooms. Ammonia may also escape from fertilizer tanks or during various manufacturing processes utilizing or making NH3. Domestic incineration and automobile engines contribute to concentrations of NH3 in urban areas.