NOXNitrogen Oxides

NOxN2O, NO, NO2+1, +2, +4 Oxidation state of NLewis dot structureSources

Important Atmospheric nitrogen oxides

Oxidation State of NitrogenN2O +1NO +2NO2 +4HNO3, N2O5 +5NO3 +6

The chemistry of atmospheric nitrogen different in troposphere than that in the stratosphere.is driven by the photochemical dissociation of nitrogen dioxide (NO2), the products formed depend on other substances with which the photo-chemically excited NO2 molecules can react

NOX ground level the air is more dense than in the troposphere, the concentration of O2 is much greater. At ground level volatile organic carbon substances (from automobile traffic, solvents and industrial processes) that react with nitrogen oxides to form peroxy-actylnitrates photochemical smog.

formation of photochemical smog.

Stratospheric nitrogen chemistryincludes ozone as a major player. The intense ultraviolet radiation causes diatomic oxygen to dissociate into oxygen atoms oxygen radical atoms react with oxygen molecules to form ozone. This sequences of reactions is known as the Chapman cycle, shown below.

Chapman cycle242 nm330 nm

Nitrogen oxides reacts with ozone

NOx reacts with Ozone (II mechanism)

Overall effectundisturbed stratosphere steady-state concentration of each of the gases involved most concerned about the ozone concentrationThe natural concentration of stratospheric ozone is 6-10 ppm, or about 350 Daltons.

N2O, NO, NO2, Nitrogen enters the atmosphere in several different forms, leaves the atmosphere by being washed with precipitation as nitric acid, HNO3 N2(g) + O2(g) 2NO(g)

NOX pollutantPrimary : NO ;Secondary : NO2N2 + O2 2NO2 NO + O2 2NO2Most of man made NOX is NO localized concentration / use of automobilesNatural decomposition of Nitrogen containing compound by bacteria : N2O, NO : widely spread

Formation of NO

Formation of NO2

Formation of HNO3

Effect on HealthToxic: NO2 > NOIrritation of eyes, noseDifficulty in breathingRespiratory distressAccumulation of fluid in the lungs ( pulmonary edemaCan lead to death

Control and PreventionCatalytic converterThermal exhaust reactor (Factors: temp, amount of O2 available), lower air to fuel ratioExhaust gas recirculation method, EGR, diagramCooler gas exhaust re-circulated into engineLowers the tempCompletes the oxidation of CO and HC(Lean burn engine reduces NO)Requires expensive engine design

Lean Burn Engine

Lean Burn EngineAir :fuel ratio 18:1Optimum ratioOptimum ratioAir to fuel ratioLean burn area18NO, CO, HC [ ]

NOx

Meteorological Station at Engineering E2 used for continuous atmospheric measurements.