The principal air-quality pollutant emissions from petrol, diesel, and alternative-fuel engines are carbon monoxide, oxides of nitrogen, un-burnt hydrocarbons and particulate matter. It is emissions of these pollutants that are regulated by the Euro emissions standards. Modern cars, if kept in good condition, produce only quite small quantities of the air quality pollutants, but the emissions from large numbers of cars add to a significant air quality problem. Carbon monoxide, oxides of nitrogen, and un-burnt hydrocarbons are gases, and are generally invisible.
Particulate matter is usually invisible although under certain operating conditions diesel engines 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. Fine particles can also be produced by tyre and brake wear. Pollutant emission levels depend more on vehicle technology and the state of maintenance of the vehicle. Unlike emissions of CO2, emission of air quality pollutants are less dependent on fuel consumption. Other factors, such as driving style, driving conditions and ambient temperature also affect them. However, as a starting point, all new passenger cars must meet minimum EU emissions standards.
The effects of these exhaust gases are described in more detail below:
CO – Carbon monoxide reduces the blood’s oxygen-carrying capacity which can reduce the 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.
NOx – Oxides of nitrogen include nitrogen dioxide (NO2 ) and nitrogen oxide (NO): NO reacts 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, and acid rain, can damage vegetation, contributes to ground-level ozone formation and can react in the atmosphere to form fine particles (‘secondary particles’).
Particulate matter (PM) – Fine particles have an adverse effect on human health, particularly among those with existing respiratory disorders. Particulate matter is associated with respiratory and cardiovascular problem. 29,000 deaths a year in the UK are attributable to fine particulate pollution.
HC – Hydrocarbons contribute to ground-level ozone formation leading to risk of damage to the human respiratory system. Some kinds of hydrocarbons, in addition, are both carcinogenic and indirect greenhouse gases.
Using less oil—and avoiding unnecessary emission from the oil we do use—is the real solution.
Fuel-efficient vehicles use less gas to travel the same distance as their less efficient counterparts. When we burn less fuel, we generate fewer emissions. When emissions go down, the pace of global warming slows.
Cleaner fuels produce fewer emissions when they’re burned. Some fuels—such as those made from cellulosic biofuels—can reduce emissions by 80 percent compared to gasoline. And better regulations would help prevent the gasoline we do use from getting any dirtier.
Electric cars and trucks use electricity as fuel, producing fewer emissions than their conventional counterparts. When the electricity comes from renewable sources, all-electric vehicles produce zero emissions to drive.
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