X
Nitrogen Oxides

• 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 photochemically excited NO react
2 molecules can

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.

• 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.

242 nm
330 nm

Nitrogen oxides reacts with ozone

NOx reacts with Ozone
(II mechanism)

• 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.

2
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)

X
• 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

• 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

• 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

N
O
,
C
O
,
H
C
[ ]
• Air :fuel ratio 18:1
Lean burn area
O p t i m m u r m r a i o
18
Air to fuel ratio

Meteorological Station at Engineering E2 used for continuous atmospheric measurements
.