CO2 is the most important of the greenhouse gases which are contributing to Climate Change. Unless action is taken to reduce emissions of greenhouse gases, such as CO2, the whole pattern of the World's weather could change, increasing the frequency and intensity of heatwaves, floods, droughts and storms.
Compared to the reductions in the emissions of toxic pollutants,as desribed below, there has been less progress on reducing CO2 from cars. For a given type of fuel the CO2 emissions of a car are directly proportional to the quantity of fuel consumed. Until recently the average fuel consumption of new cars changed slowly.
This was because while engines had become more efficient over this period, average vehicle mass had increased due to additional features to meet crash safety requirements and the widespread addition of features such as power assisted steering and air conditioning.
However, at the Kyoto Conference on climate change in 1997, most developed countries agreed to legally binding targets to reduce their greenhouse gas emissions in response to warnings over global climate change.
Arising from this, the European Commission and industry associations of the major manufacturers selling in the EU, agreed in 1998 to reduce the average g/km carbon dioxide emissions of new cars. These voluntary targets would reduce this figure by over 25% by 2008/9, to 140g/km. Average fuel consumption has therefore dropped somewhat as a result of these voluntary agreements
The other pollutants from petrol, diesel and alternative fuel engines are mainly Carbon Monoxide, Oxides of Nitrogen, un-burnt Hydrocarbons and fine particles. The first three are gases and are invisible.
Fine particles are usually invisible although in certain operating conditions diesels will produce visible particles, appearing as smoke. Petrol engines will also produce visible particles if they are burning engine oil or running rich, for example, following a cold start.
Unlike CO2, emissions of these pollutants are not directly linked to fuel consumption. Pollutant levels are more dependent on vehicle technology and the state of maintenance of the vehicle. Other factors, such as driving style, driving conditions and ambient temperature also affect emission of pollutants.
However, as a starting point new passenger cars must meet minimum EU emissions standards.
The effects of these exhaust gas pollutants and their effects are described in more detail below:
Carbon Monoxide reduces the blood’s Oxygen carrying capacity which can reduce availability of Oxygen to key organs. Extreme levels of exposure, such as might occur due to blocked flues in domestic boilers, can be fatal. At lower concentrations CO may pose a health risk, particularly to those suffering from heart disease.
Oxides of Nitrogen react in the atmosphere to form Nitrogen Dioxide (NO2) which can have adverse effects on health, particularly among people with respiratory illness. High levels of exposure have been linked with increased hospital admissions due to respiratory problems, while long term exposure may affect lung function and increase the response to allergens in sensitive people. NOx also contributes to smog formation, acid rain, can damage vegetation, contributes to ground level Ozone formation and can react in the atmosphere to form fine particles (‘secondary particles’).
Fine particles can have an adverse effect on human health, particularly among those with existing respiratory disorders. Particles have been associated with increased hospital admissions due to respiratory and cardiovascular problems, bringing forward the deaths of those suffering from respiratory illnesses and a reduction in life expectancy.
Hydrocarbons, contribute to ground level Ozone formation leading to risk of damage to the human respiratory system. In addition, some kinds of HCs are carcinogenic and they are also indirect greenhouse gases.
The Government is convinced that action to reduce harmful emissions must continue. Its approach to tackling air pollution is set out in the Air Quality Strategy for England, Scotland, Wales and Northern Ireland. This sets health based standards for eight main air pollutants, from which air quality objectives are derived, together with a timescale for their achievement.
The Strategy identifies the action required at a national and international level, and the contribution industry, transport and local government can make to ensure objectives are met.
Achieving the air quality standards for Nitrogen Dioxide and fine particles presents the greatest challenge, especially in urban areas and close to busy roads. Emissions of the above pollutants are being reduced by improving the quality of fuels and by setting increasingly stringent emission limits for new vehicles.