language-icon Old Web
English
Sign In

NOx

In atmospheric chemistry, NO x is a generic term for the nitrogen oxides that are most relevant for air pollution, namely nitric oxide (NO) and nitrogen dioxide (NO 2 ). These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone. NO 2 + h ν ⟶ NO + O   ( 3 P ) , λ < 424 nm {displaystyle {ce {NO2 + h u -> NO + O (^3P)}},qquad lambda <424{ce {nm}}}     (1) O   ( 3 P ) + O 2 + M ⟶ O 3 + M {displaystyle {ce {O (^3P) + O2 + M -> O3 + M}}}     (2) O 3 + NO ⟶ NO 2 + O 2 {displaystyle {ce {O3 + NO -> NO2 + O2}}}     (3) [ NO 2 ] [ NO ] = k 3 [ O 3 ] j NO 2 {displaystyle {frac {{ce {}}}{{ce {}}}}={frac {k_{3}}{j_{{ce {NO2}}}}}}     (4) τ = 1 k 3 [ NO ] {displaystyle au ={frac {1}{k_{3}}}}     (5) In atmospheric chemistry, NO x is a generic term for the nitrogen oxides that are most relevant for air pollution, namely nitric oxide (NO) and nitrogen dioxide (NO 2 ). These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone. NO x gases are usually produced from the reaction among nitrogen and oxygen during combustion of fuels, such as hydrocarbons, in air; especially at high temperatures, such as occur in car engines. In areas of high motor vehicle traffic, such as in large cities, the nitrogen oxides emitted can be a significant source of air pollution. NO x gases are also produced naturally by lightning. The term NO x is chemistry shorthand for molecules containing one nitrogen and one or more oxygen atom. It is generally meant to include nitrous oxide (N2O), although nitrous oxide is a fairly inert oxide of nitrogen that has many uses as an oxidizer for rockets and car engines, an anesthetic, and a propellant for aerosol sprays and whipped cream. Nitrous oxide plays hardly any role in air pollution, although it may have a significant impact on the ozone layer, and is a significant greenhouse gas. NO y is defined as the sum of NO x plus the NO z compounds produced from the oxidation of NO x which include nitric acid, nitrous acid(HONO), dinitrogen pentoxide(N2O5), peroxyacetyl nitrate(PAN), alkyl nitrates (RONO2), peroxyalkyl nitrates (ROONO2), the nitrate radical (NO3), and peroxynitric acid(HNO4).:30 Because of energy limitations, oxygen and nitrogen do not react at ambient temperatures. But at high temperatures, they undergo an endothermic reaction producing various oxides of nitrogen. Such temperatures arise inside an internal combustion engine or a power station boiler, during the combustion of a mixture of air and fuel, and naturally in a lightning flash. In atmospheric chemistry, the term NO x denotes the total concentration of NO and NO 2 since the conversion between these two species is rapid in the stratosphere and troposphere. During daylight hours, these concentrations together with that of ozone are in steady state, also known as photostationary state(PSS); the ratio of NO to NO 2 is determined by the intensity of sunshine (which converts NO 2 to NO) and the concentration of ozone (which reacts with NO to again form NO 2 ).

[ "Combustion", "Peroxyacetyl nitrate", "Non-road engine", "FTP-75", "Selective catalytic reduction", "Waste Incineration Directive" ]
Parent Topic
Child Topic
    No Parent Topic