Author: Tara Alderson

Date: 12/8/10


Exhaust is the waste product of internal-combustion engines found in most passenger vehicles such as cars, trucks, buses, ferries, ships, and planes. Internal-combustion engines produce exhaust by a process in which air is ingested into a chamber, then either the air is compressed and fuel is introduced into the compressed air, or, the fuel is introduced to the air then this air/fuel mixture is compressed together. The compressed air/fuel mixture is then burned in order to cause an expansion that moves vehicle parts. The burning of the compressed air/fuel mixture creates a hot gaseous product called exhaust that is ultimately released through the exhaust system. [1]

Engine deterioration

Engine deterioration is the prime factor in the decline of emission quality, especially in high mileage, public service and commercial vehicles. Unfortunately, engine deterioration is not part of the existing inspection criteria in Hong Kong – instead, an easy to meet emission standard is applied to all vehicles whether just 2 or over 10 years old. [2]

Environmentally friendly engines?

There is no such thing as an “Environmentally friendly internal combustion engine”, because all these engines suck in large amounts of air and exhaust larger and much hotter amounts of gaseous substances which are harmful to our environment. [3]

Electric vehicles do not produce pollution directly but when considering the source of electricity some electric vehicles may produce more emissions in the end; electricity derived from a coal fired power plant emits pollution whereas electricity derived from renewable sources such as wind, solar, geothermal or wave produce none. [4]

Electricity production

Coal-fired power plants produce electricity by first: pulverizing coal into a fine powder; second, mixing it with air and blowing it into a boiler where it ignites immediately; and third; pumping millions of litres of purified water through tubes inside the boiler to produce steam; this steam spins the turbine to create electricity. Burning coal produces carbon dioxide (CO2), sulphur dioxide (SO2) and nitrogen oxides (NOx). [5]

Dispersal of primary pollutants

The dispersion of air pollutants depends on wind and weather conditions, particle size of pollutants, and the height from which the pollutant is emitted. [6]


  1. ‘Internal combustion engine’ – Encyclopedia Brittanica
  2. Fung Man Keung, Lecturer, Dept of Automotive Engineering, Hong Kong Institute of Vocational Training, 1/10/05
  3. ‘Hong Kong: Vehicle Related Air Pollution in Support of Action Blue Sky’, Ir Iain Seymour-Hart, October 2007
  4. ‘Will Electric Vehicles really produce Pollution?’ (1997) – last accessed 12/8/10
  5. ‘How a coal plant works’ (2010) Canadian Clean Power Coalition – last accessed 12/8/10
  6. FAQ air pollution, (2009). Lenntech BV - last accessed 7/8/10