Environmental benefits of autogas

Road-transport vehicles are an important source of both air pollutants and climate-destabilising greenhouse gases. There is clear evidence of the harmful impact on human health of exposure to vehicle pollutants. As a result, local air quality has become a major policy issue in almost all countries. Most industrialised countries have made substantial progress in reducing pollution caused by cars and trucks through improvements in fuel economy, fuel quality and the installation of emission-control equipment in vehicles. Increasingly, these improvements have been driven by emission standards. However, rising road traffic has offset in most countries at least part of the improvements in vehicle-emissions performance. Less progress has been made in developing countries, where local pollution in many major cities and towns has reached catastrophic proportions.


The European Union and the United States have been the main driving forces behind vehicle emissions standards. Every developed country and most developing countries have progressively introduced these or similar standards for new vehicles. The international nature of vehicle manufacturing and trade has prompted increasing harmonisation of standards and regulation. The most broadly implemented standards, generally referred to as Euro regulations, are those developed by the United Nations Economic Commission for Europe (UNECE), which are uniformly applied across the European Union and in many other parts of the world. Different standards are applied to light-duty vehicles (essentially passenger cars and vans, in most cases with a maximum gross weight of less than 3.5 tonnes) and heavy-duty vehicles (trucks and buses). These standards have been tightened periodically, typically every four to five years, since they were first introduced in 1992. Euro 5 regulations are currently in force. The United States has its own regulations, but work is proceeding to unify the two systems.

Governments are also looking increasingly at ways of encouraging a shift in fuel use to alternative fuels that can yield a reduction in climate-destabilising emissions of greenhouse-gases at least cost. Globally, road transport has become the second-largest source of emissions of carbon dioxide – the leading greenhouse gas – after power generation, accounting for well over one-fifth of total emissions. Emission standards for CO2 have not yet been applied.

Autogas out-performs gasoline and diesel and most alternative fuels in the majority of studies comparing the environmental performance of conventional and alternative fuels that have been conducted around the world in recent years. Autogas emissions are especially low with respect to noxious pollutants. With regard to greenhouse-gas emissions, autogas performs better than gasoline and, according to some studies, out-performs diesel, when emissions are measured on a full fuel-cycle, or well-to-wheels, basis and when the LP Gas is sourced mainly from natural gas processing plants (see below).

The results of these studies vary to some degree, according to the types of vehicles selected, the quality of the fuel, the types of emissions measured and the conditions under which they were carried out vary: actual vehicle emissions are highly dependent on vehicle technology and driving behaviour. The rest of this section summarises the results of the main studies for lightduty and heavy-duty vehicles.

Light-duty vehicle emissions

Regulated pollutant emissions


International Journal of Civil and Environmental Engineering 1:4 2009


 Chart 4

Graph of CO in urban cycle


Chart 5

Graph of CO in extra urban cycle


Chart 6

Graph of HC in urban cycle


Chart 7

Graph of HC in extra urban cycle


Chart 7

Graph of NOx in urban cycle


Chart 7

Graph of NOx in extra urban cycle


Chart 7

Graph of CO2 in urban cycle


Chart 7

Graph of CO2 in extra urban cycle


CO2 - Carbon di oxide

PPM - Parts per million

RON - Research octane number

MAP - Manifold absolute pressure

O2 - Oxygen


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