Main Vehicle Emissions


* Oxides of Nitrogen (Nox).
* Volatile Organic Compounds (VOC).
* Particulate Matter (PM10 & PM25).
* Carbon Dioxide (Co2).
* Carbon Monoxide (Co).
* Toxics.
* Hydrocarbons (Unburnt Fuel – Hc).

Particulate Matter (PM10 & PM2.5):
Particulate matter (PM10 and PM2.5)
The health effects of inhaling airbourne particulate matter have been widely studied in humans and animals and include asthma, lung cancer, cardiovascular issues, and premature death. Because of the size of the particles, they can penetrate the deepest part of the lungs. A 2011 UK study estimates 90 deaths per year due to passenger vehicle PM. In a 2006 publication, the U.S. Federal Highway Administration (FHWA) state that in 2002 about 1 per-cent of all PM10 and 2 per-cent of all PM2.5 emissions came from the exhaust of on-road motor vehicles (mostly from diesel engines).
What is Diesel Particulate Matter?
Diesel particulate matter is part of a complex mixture that makes up diesel exhaust. Diesel exhaust is composed of two phases, either gas or particle.
The gas phase is composed of many of the urban hazardous air pollutants, such as acetaldehyde, acrolein, benzene, 1,3-butadiene, formaldehyde and polycyclic aromatic hydrocarbons.
The particle phase also has many different types of particles that can be classified by size or composition. The size of diesel particulates that are of greatest health concern are those that are in the categories of fine, and ultra fine particles. The composition of these fine and ultra fine particles may be composed of elemental carbon with adsorbed compounds such as organic compounds, sulfate, nitrate, metals and other trace elements.
Diesel exhaust is emitted from a broad range of diesel engines; the on road diesel engines of trucks, buses and cars and the off road diesel engines that include locomotives, marine vessels and heavy duty equipment.

Oxides of Nitrogen (NOx):
Mono-nitrogen oxides NO and NO2 (whether produced this way or naturally by lighting) react with ammonia, moisture, and other compounds to form nitric acid  vapour and related particles. Small particles can penetrate deeply into sensitive lung tissue and damage it, causing premature death in extreme cases. Inhalation of such particles may cause or worsen respiratory diseases such as emphysema and bronchitis. It may also aggravate existing heart disease. In a 2005 U.S. EPA study the largest emissions of NOx came from on road motor vehicles, with the second largest contributor being non-road equipment which is mostly gasoline and diesel stations.
The resulting nitric acid may be washed into soil, where it becomes nitrate, which is useful to growing plants.
Diesel exhaust gas is produced inside diesel engines, where conditions differ considerably from spark-ignition engines. Diesel engine power is directly controlled by the fuel supply, not by control of the air/fuel mixture as in conventional gasoline engines. When a diesel engine runs at idle, enough oxygen is present to burn the fuel completely. Diesel engines only make significant amounts of soot when running without enough oxygen.
It is reported that emissions from diesel vehicles are significantly more harmful than those from petrol ones. Diesel exhaust contains toxic air contaminants and is listed as carcinogen for humans by the IARC (part of the World Health Organization- WHO of the United Nations – UN). Diesel exhaust contains fine particles which are harmful. Diesel exhaust pollution was thought to account for around one quarter of the pollution in the air in previous decades, and a high share of sickness caused by automotive pollution.
Diesel exhaust has been known for its characteristic smell, which became much less when the Sulfur content of diesel fuel was reduced, and again became less when catalytic converters were used in exhaust systems.
The lean-burning nature of diesel engines and the high temperatures and pressures of the combustion process result in significant production of nitrogen oxides, and provide a unique challenge in reducing these compounds. Modern on-road diesel engines typically use selective non-catalytic reduction to meet emissions laws, as other methods such as Exhaust Gas Recirculation (EGR) cannot adequately reduce NOx to meet newer standards in many jurisdictions. However, the fine particulate matter in the exhaust fumes (sometimes visible as opaque dark-colored smoke) has traditionally been of greater concern, as it presents different health concerns and is rarely produced in significant quantities by spark-ignition engines. It is reported in 2012 that although total nitrogen oxides from petrol cars have decreased by around 96% through adoption of exhaust catalyst, diesel cars still produce nitrogen oxides at a similar level to those bought a decade and a half ago under real world tests, resulting in diesel cars emit around 20 times more nitrogen oxides than petrol cars.
Diesel engines produce very little carbon monoxide as they burn the fuel in excess air even at full load, at which point the quantity of fuel injected per cycle is still about 50 percent less than the stoichiometric requirement.

Exhaust Gas Recirculation (EGR):
Recirculating exhaust gas from the exhaust manifold of a diesel engine into an EGR valve which is timed to coincide with the intake valves, allow some exhaust back into the cylinder for compression and the power stroke. Thus less fuel is used on the power stroke, thereby avoiding engine knock, letting the engine run on a much leaner fuel to air ratio, giving the engine better fuel economy and less gaseous emissions. However, with this system there is more particulate exhaust, which requires a Particulate Matter (PM) filter in the exhaust. EGR needs a pressure differential across the exhaust manifold and intake manifold. This needs a variable geometry turbocharger, which has inlet guide vanes on the turbine to build exhaust backpressure in the exhaust manifold directing exhaust gas to the intake manifold. It needs external piping and a valve that would need more maintenance.
Another way of achieving an EGR-like effect is valve cam overlap whereby the intake and exhaust valves remain open simultaneously for a period.
All these systems are controlled by an electronic engine control unit (ECU) for the optimized minimum of pollutants released in the exhaust gas. The vehicle manufactures in conjunction with the service provider “map” the electronic control unit thus optimize the range of engine performance during various operating conditions to achieve emission outputs.

Biodiesel and NOx
Biodiesel and its blends in general are known to produce lower carbon monoxide, soot, hydrocarbon emissions, and higher NOx emissions compared with regular diesel. Because of the lower heating value of biodiesel, more biodiesel should be burned to produce the equivalent energy. Also, due to the presence of high oxygen content in biodiesel fuels, generally biodiesel fuels emit more NOx than regular diesel for the same heat generation. The reduction of NOx emissions is one of the most important technical challenges facing biodiesel, especially in light of the increasingly stringent exhaust emission regulations on diesel engines. NOx formation during biodiesel combustion is associated with a number of factors such as the property of biodiesel and combustion conditions. Combustion temperature influences thermal NOx emissions. Therefore, low-temperature may help thermal NOx reduce during combustion, leading to low-temperature combustion or LTC technology.

Volatile Organic Compounds (VOC):

Volatile organic compounds, sometimes referred to as VOCs, are organic compounds that easily become vapours or gases. Along with carbon, they contain elements such as hydrogen, oxygen, fluorine, chlorine, bromine, sulphur or nitrogen.

Volatile organic compounds are released from burning fuel, such as petrol, wood, coal, or natural gas. They are also emitted from diesel exhausts, solvents, paints and glues.

Many volatile organic compounds are also hazardous air pollutants. VOC’s, when combined with nitrogen oxides (NOX), react to form ground-level ozone, or smog, which contributes to climate change.

Examples of volatile organic compounds are petrol, benzene, and formaldehyde, solvents such as toluene, styrene, and perchloroethylene.

Many volatile organic compounds are commonly used in paint thinners, lacquer thinners, air fresheners, aerosol sprays, degreasers and automotive products in general.
When oxides of nitrogen (NOx) and Volatile Organic Compounds (VOCs) react in the presence of sunlight, ground level Ozone is formed, a primary ingredient in smog.
Ozone is beneficial in the upper atmosphere, but at ground level, ozone irritates the respiratory system, causing coughing, choking, and reduced lung capacity. It also has many bad effects throughout the ecosystem.

Sulphur Dioxide (SO2)

Sulphur occurs naturally in the crude oil from which petrol and diesel are refined. It forms acids on combustion, leading to acid rain and engine corrosion. It also contributes to the formation of ozone and of particulate matter. Sulphur can also adversely affect the performance of catalytic converters and is now removed from both petrol and diesel during the refining process.

Sulphur dioxide is a gas. It is invisible and has a nasty, sharp smell. It reacts easily with other substances to form harmful compounds, such as sulphuric acid, sulphurous acid and sulphate particles.

About 99% of the sulphur dioxide in air comes from human sources. The main source of sulphur dioxide in the air is industrial activity that processes materials that contain sulphur, example: the generation of electricity from coal, oil or gas that contains sulphur.

Sulphur dioxide is present in motor vehicle emissions, as the result of fuel combustion. Those most at risk of developing problems if they are exposed to sulphur dioxide are people with asthma or similar conditions.

What’s being done to manage sulphur dioxide?

  • Implement national fuel quality standards;
  • Support the implementation of tighter vehicle emission standards; and
  • Promote alternative fuels.


Carbon dioxide (CO2)

Carbon dioxide is a greenhouse gas. Motor vehicle CO2 emissions are part of the anthropogenic contribution to the growth of CO2 concentrations in the atmosphere which is causing climate change. Motor vehicles are calculated to generate about 20% of the European Union’s man-made CO2 emissions, with passenger cars contributing about 12%. European emission standards limit the CO2 emissions of new passenger cars and light vehicles.

Carbon Dioxide (C02) – a non – toxic gas but contributes towards acidification. Governments around the world are pursuing polices to reduce C02 emissions to combat global warming.

Carbon monoxide (CO)

Satellite computer image of carbon monoxide - March 2010.
Satellite computer image of carbon monoxide – March 2010.

Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Carbon monoxide is colourless, odourless and tasteless, but highly toxic. It combines with haemoglobin to produce carboxyhemoglobin, which is ineffective for delivering oxygen to bodily tissues.

Carbon monoxide is a product of incomplete combustion of organic matter due to insufficient oxygen supply to enable complete oxidation. It is often produced in domestic or industrial settings by vehicles that run on petrol, diesel, or other carbon-based fuels.
Exposure at 100 ppm (parts per million) or greater can be dangerous to human health.

Air Quality in Ireland 2014 (Published 2015 by EPA).

Summary: Ambient air quality trends based on concentration measurements in 2014 of particulate matter, sulphur dioxide, nitrogen oxides, black smoke, heavy metals, ozone, polycyclic aromatic hydrocarbons, carbon monoxide and benzene.

Link to Document

Heavy Metals:

Lead, arsenic, cadmium, nickel and mercury are toxic heavy metals, which can be found in the air. They impact on health through inhalation of particulate matter containing the metals or, in the case of mercury, direct inhalation of vapour.

Heavy metals can enter the food chain through deposition to the ground (soil contamination). Their sources are primarily fossil fuel combustion, industrial processes such as metal‐plating, mining, smelting, the production of batteries, plastics and pigments and other sources. Lead was used in many products such as paint in the past. The most common source of lead was emissions from motor vehicles; however, this has dramatically reduced since the introduction of lead‐free petrol in the 1980s.

Mercury is also a toxic heavy metal which can be found in the atmosphere. The majority of mercury emissions to the atmosphere are from natural sources such as volcanoes.

Anthropogenic sources of atmospheric mercury include: unabated coal combustion; gold production and metal smelting. Heavy metal deposition from air pollution can also have a significant impact on water quality. This is especially true with respect to mercury. 9.2 Air quality standards for heavy metals Table 9.1 shows the air quality target values for the heavy metals arsenic, cadmium and nickel and the limit value for lead.

Air quality limit and target values for As, Cd, Ni and Pb as set out in S.I. No. 58 of 2009. Reference to Heavy Metals is also made within the End of Life Vehicle Directive.

SI 661 of 2011 Ban of Heavy Metals (Annex II – Directive 2000/53/EC End of Life Vehicles ELV).