1.2 Photochemical Smog Flashcards
Write the equations for the formation of nitrogen oxides NO & NO2 when sufficient energy is present (include colours)
Nitrogen Monoxide - colourless gas
N2 + O2 –> 2NO
Nitrogen Dioxide (Brown gas)
2NO + O2 –> 2NO2
What gases are associated with photochemical smog?
Nitrogen oxides and ozone
Process of nitrogen oxides to ozone in troposphere
Sunlight causes photochemical decomposition of NO2
NO2 –> NO + O (FREE RADICAL)
Free Radical O reacts with O2
O (FREE RADICAL) + O2 + M –> O3 + M (FREE RADICAL)
What is photochemical smog?
Yellowish brown haze.
Forms when primary pollutants enter a series of photochemical reactions which produce a mixture of nitrogen oxides, free radicals, aldehydes and ozone.
When will photochemical smog form?
On sunny days with little wind
What are the primary pollutants?
The direct result of the oxidations of nitrogen (NO) and any unburnt hydrocarbons from the exhaust of cars.
What are the secondary pollutants?
NO2, O3 and any products of the unburnt hydrocarbons.
Health effects of photochemical smog
irritating to respiratory track, skin and eyes.
Environmental concerns of photochemical smog
O3 is highly corrosive and reactive:
- attacks mucus of respiratory track, eyes and rubber
- leaves plants yellow
- reduce rate of photosynthesis
ACID RAIN??
What is a catalytic convertor?
Placed in the exhaust of cars to reduce the formation of photochemical smog.
Includes a very thin layer of platinum group metals in a honeycomb structure.
It will not work unless car engine is warmed up so catalysts are at optimum temperature.
Equations of catalytic convertor (Occur due to contact with catalyst metals)
Oxidation of carbon monoxide to carbon dioxide 2CO + O2 --> 2CO2 Combustion of unburnt hydrocarbons 2C8H18 + 25O2 --> 16CO2 + 18H2O Nitrogen oxide reduced to nitrogen gas 2CO + 2NO --> N2 + 2CO2
Why is there a build up of NO in the early morning?
A build up of traffic due to commute to work. NO is formed by the combustion of N2 in the engines of motor vehicles.
Why is photo chemical smog not as prevalent in the later evening?
There is less sunlight. There is less intense UV radiation. Some reactions require sunlight and thus the photochemical smog reduces.
Oxidation convertor reactions
NOx –> N2 + O2
Reduction convertor equations
2CO + O2 –> 2CO2
