Nitrogen Oxides - NOx
Nitrogen oxides include the gases nitrogen oxide (NO) and nitrogen dioxide (NO2). NOx is formed primarily from the liberation of nitrogen contained in fuel and nitrogen contained in combustion air during combustion processes. NO emitted during combustion quickly oxidizes to NO2 in the atmosphere. NO2 dissolves in water vapour in the air to form acids, and interacts with other gases and particles in the air to form particles known as nitrates and other products that may be harmful to people and their environment.
Both NO2 in its untransformed state, and the acid and nitrate transformation products of NO 2 , can have adverse effects on human health or the environment. NO2 itself can cause adverse effects on respiratory systems of humans and animals, and damage to vegetation. When dissolved by water vapour, the acids formed can have adverse effects on the respiratory systems of humans and animals. Nitric acid (HNO3) can cause damage to vegetation, buildings and materials, and contribute to acidification of aquatic and terrestrial ecosystems. When NO2 is transformed into nitrate particles that are subsequently deposited on aquatic and terrestrial ecosystems, acidification can result. When nitrate is combined with other compounds in the atmosphere, such as ammonia, it becomes an important contributor to the secondary formation of respirable particulate matter (PM2.5). NO2 is one of the two primary contributing pollutants, along with volatile organic compounds (VOCs), to the formation of ground-level ozone. Both ozone and PM2.5 is known to have harmful effects on human health and the environment.
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