NO X Nitrogen Oxides

NOx N2O, NO, NO2 +1, +2, +4 Oxidation state of N Lewis dot structure Sources

Important Atmospheric nitrogen oxides Oxidation State of Nitrogen N2O +1 NO +2 NO2 +4 HNO3, N2O5 +5 NO3 +6

The chemistry of atmospheric nitrogen different in troposphere than that in the stratosphere. is driven by the photochemical dissociation of nitrogen dioxide (NO 2 ), the products formed depend on other substances with which the photo- chemically excited NO 2 molecules can react

NO X ground level the air is more dense than in the troposphere, the concentration of O 2 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 chemistry includes 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 cycle 242 nm 330 nm

Nitrogen oxides reacts with ozone

NOx reacts with Ozone (II mechanism)

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

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

NO X pollutant Primary : NO ;Secondary : NO 2 N 2 + O2 2NO 2 NO + O 2 2NO 2 Most of man made NOX is NO localized concentration / use of automobiles Natural decomposition of Nitrogen containing compound by bacteria : N 2 O, NO : widely spread

Formation of NO

Formation of NO2

Formation of HNO3

Effect on Health Toxic: NO 2 > NO Irritation of eyes, nose Difficulty in breathing Respiratory distress Accumulation of fluid in the lungs ( pulmonary edema Can lead to death

Control and Prevention Catalytic converter Thermal exhaust reactor (Factors: temp, amount of O 2 available), lower air to fuel ratio Exhaust gas recirculation method, EGR, diagram –Cooler gas exhaust re-circulated into engine –Lowers the temp –Completes the oxidation of CO and HC –(Lean burn engine reduces NO) –Requires expensive engine design

Lean Burn Engine

Air :fuel ratio 18:1 Optimum ratioOptimum ratio O p ti m u m r a ti o Air to fuel ratio Lean burn area 18 N O, C O, H C [ ]

NOx

Meteorological Station at Engineering E2 used for continuous atmospheric measurements.