What are the sources of nitrogen oxide emissions?

1. Naturally emitted NOx primarily comes from the decomposition of organic matter in soil and oceans, and is part of the natural nitrogen cycle. 2. Most of the NO emitted due to human activities comes from the combustion of fossil fuels, such as in cars, airplanes, internal combustion engines, and industrial furnaces ； It also comes from the processes of producing and using *ao acid, such as nitrogen fertilizer plants, organic intermediate factories, and smelters of non-ferrous and ferrous metals. NOx causes significant damage to the environment; it is one of the main substances that contribute to acid rain, as well as a key component in the formation of photochemical smog in the atmosphere, and it is also an important factor in the depletion of O3.

Nitrogen oxides in the air include nitrous oxide (N2O), nitrogen monoxide (NO), nitric oxide (NO2), dinitrogen trioxide (N2O3), etc. The main components among them are nitrogen monoxide and nitric oxide, which are referred to as NOx (nitrogen oxides). NOx pollution primarily stems from the combustion of fuels such as coal and oil used in production and daily life (including the NOx emitted by cars and all internal combustion engines) ； Next are the exhaust gases emitted by factories that produce or use *ao acid. When NOx and hydrocarbons are present in the air, they undergo photochemical reactions under the action of sunlight’s ultraviolet rays, resulting in the formation of photochemical smog, which is a toxic secondary pollutant. NO2 is 4 times more toxic than NO; it can cause lung damage and even lead to pulmonary edema. Chronic exposure can result in lesions in the trachea and lungs. Inhaling NO can lead to the formation of methemoglobin and have an impact on the central nervous system. The concentration at which NOx has an effect on animals is roughly 1.0 milligrams per cubic meter, while for humans it is about 0.2 milligrams per cubic meter. **** Environmental quality standards stipulate that the average concentration in residential areas should be below 0.10 milligrams per cubic meter, with the annual average concentration being below 0.05 milligrams per cubic meter.