DF10 Flashcards
What is a primary pollutant?
An air pollutant emitted directly from a source.
What are secondary pollutants?
When primary pollutants react in the atmosphere.
What are some of the primary pollutants (from vehicles and other sources)?
- particulates
- volatile organic compounds (VOC)
- carbon monoxide (CO)
- carbon dioxide (CO2)
- nitrogen oxides (NOx)
- sulfur oxides (SOx)
What are particulates?
Particularly small carbon particles smaller than 2.5 x 10^-12 m.
What are the major sources of particulates?
- volcanoes
- burning fuels
- burning coal
What are the major polluting effects of particulates?
Penetrate deep into the human body - causing heart attacks and lung cancer.
What are the major sources of VOC?
- plants
- unburnt fuel from petrol engines
What are the major polluting effects of VOC?
photochemical smog
What are the major sources of CO?
- incomplete combustion of hydrocarbons in fossil fuels
- burning biomass
What are the major polluting effects of CO?
- toxic gas
- photochemical smog
What are the major sources of CO2?
combustion of fossil fuels
What are the major polluting effects of CO2?
greenhouse effect
What are the major sources of NOx?
combustion of fuels in power stations and vehicles
What are the major polluting effects of NOx?
- acid rain
- photochemical smog
What are the major sources of SOx?
- volcanoes
- burning of fuels containing sulfur
What are the major polluting effects of SOx?
- toxic gas
- acid rain
What is the equation for complete combustion?
hydrocarbon/alcohol + oxygen → carbon dioxide + water
What is the equation for incomplete combustion?
hydrocarbon/alcohol + oxygen → CO + C + water
Why does incomplete combustion occur?
Limited supply of oxygen - either CO or C produced (and water).
How is SO2 produced from fuels?
Burning of sulfur compounds in fuels:
S + O2 → SO2
How are NOx produced from fuels?
Burning of nitrogen compounds in fuels:
N2 + O2 → 2NO
How are NOx produced from vehicles?
- burning in fuels
- nitrogen and oxygen in the air react in very high temperatures of a vehicle engine
How is acid rain produced from SOx?
- SO2 + H2O → H2SO3 (atmosphere)
- then SO2 is oxidised to make SO3 in stratosphere
- SO3 + H2O → H2SO4
How is acid rain produced from NOx?
2NO/2NO2 + H2O + 1.5O2 → 2HNO3 (atmosphere)
What are the harmful effects of acid rain?
- breathing difficulties
- corrodes limestone buildings
- kills forests
- kills life in lakes
How is photochemical smog produced?
When primary pollutants absorb sunlight to produce secondary pollutants (e.g. ozone, NO2, nitric acid).
What are the harmful effects of photochemical smog?
- haziness
- reduced visibility in air
- respiratory problems in humans
How are pollutants removed in petrol engines?
CO: 2CO + O2 → 2CO2
hydrocarbons: complete combustion
NO: 2NO + CO → N2 + 2CO2
Where do the reactions to remove pollutants in petrol engines occur?
In a three-way catalytic converter - consisting of platinum/rhodium (on a porous support).
How are SOx pollutants best prevented?
Removing sulfur impurities from fuels.
What are the main pollutants present in diesel engines?
- CO
- hydrocarbons
- particulates
- NOx compounds
How are CO and hydrocarbons removed in diesel engines?
CO: 2CO + O2 → 2CO2
hydrocarbons: complete combustion
How are particulates removed in diesel engines?
- diesel particulate filters
- regeneration (burning it off)
How are NOx compounds removed in diesel engines?
- Recycle some of the exhaust gases through the cylinder, lowering the temperature and amount of NOx formed.
- Reagent (e.g. ammonia) is used rather than a catalyst
How are is SO2 best prevented?
Using ultra low-sulfur fuels
