Loading...
WHAT IS AIR POLLUTION2018-08-02T13:57:12+00:00

Air pollution is made up of gases or particles in the air which are harmful to humans and other life. The impact to humans is bigger the higher the concentration, and the greater the exposure. For some pollutants, there is no safe limit and exposure to even fairly low concentrations is harmful.

The most concerning pollutants within Bristol are nitrogen dioxide (NO2) and particulate matter. Particulate matter is defined by the size of the microscopic particles, as this affects the impact it has on health.

NOx is mainly from road traffic, particularly diesel engines. When this is released into the air, it turns into NO2 through reactions with other pollutants and sunlight.

How different types of vehicle contribute to air pollution

Different types of vehicles contribute to air pollution in different ways, as shown in the graph below.

Diesel vehicles contribute 96% of the nitrogen oxide pollution in Bristol. This is mainly caused by diesel cars (40%) followed by buses and coaches (23%) and diesel vans (22%).

The Council and Government are investing large amounts of money to reduce the pollution which buses create.

Figure 4 Nitrogen Dioxide emissions from traffic in central Bristol

*Note that buses carry far more passengers than cars for their proportion of emissions; the chart does not reflect that.

Chart 1

Vehicles sold in the UK need to comply with European regulations for air pollution. These are referred to as the EURO standards and have reduced the allowable pollution emitted from vehicle exhausts at each revision. The current standards for the newest cars are known as Euro 6 (cars sold from 2015 onwards).

Many vehicles emit more pollution when driven in the real world than they do in the laboratory tests. The diagram below shows the UK government’s data on emissions from different car types. It shows that diesels emit much more NOx than petrol cars, and that the gap between the test standard and average real world performance is much greater for diesels.

Nitrogen Dioxide emissions from different car types

Chart 2

Particulate matter comes from exhausts, vehicle braking and tyres. It is also emitted from the burning of both industrial solid fuels and household wood burners – historically a very small factor, but with the massive growth in wood burners, this could change.

Tests show that a modern, efficient, Defra (Government)-approved wood burning stove should not produce enough PM to be a health problem. However there are stoves that are not Defra approved. People also burn waste wood including, composite materials (ply, MDF and chipboard), treated timber (tannalised, varnished, painted etc) and unseasoned wood with a 15% – 20% + moisture content. All these things produce pollutants that can harm human health.

Fine Particles

PM10 and PM2.5 are classifications of different sizes of particle. PM10 and PM2.5 refer to particles of equal to or less than this size in micrometres (0.001mm). Larger particles can be visible in the form of smoke;

NO2 is completely invisible. PM10 and PM2.5 are invisible too. This can be a factor in society’s failure to date to address the problem.

Bristol City Council is concerned about both NO2 and PM. At the moment NO2 is the top priority for a number of reasons, not least the legal requirement for us to reduce it.

Useful Links

Air pollution is gases or particles in the air that are harmful to humans and other life. The higher the concentrations and the more exposure to humans, the greater the impact For some pollutants there is no safe limit and exposure to even fairly low concentrations is harmful.

The main pollutants of concern within Bristol are nitrogen dioxide (NO2) and particulate matter, which is defined by the size of the microscopic particles as this is important in its health

NO2 is mainly from road traffic, particularly diesel engines – what is particulate matter and what causes it??

Pollution Contribution of Different types of vehicles

Different types of vehicles contribute to air pollution in different ways, as shown in the graph below*

Diesel vehicles contribute 96% of the nitrogen oxide pollution from the transport sector. This is primarily caused by diesel cars (40%) followed by buses and coaches (23%) and diesel vans (22%). Significant investment, with support from the council and government, is taking place within the commercial bus fleet to reduce the pollution the buses create.

Figure 4 Nitrogen Dioxide emissions from traffic in central Bristol

*Note that buses carry far more passengers than cars for their proportion of emissions; the chart does not reflect that.

Chart 1

Vehicles sold in the UK need to comply with European regulations for air pollution. These are referred to as the EURO standards and have reduced the allowable pollution emitted from vehicle exhausts at each revision. The current standards for the newest cars are known as Euro 6 (reduced from ?).

Many vehicles emit more pollution when driven in the real world than they do in the laboratory tests. The diagram below shows the UK government’s data on emissions from different car types. It shows that diesels emit much more pollution than petrol cars and that the gap between the test standard and average real world performance is much greater for diesels.

Nitrogen Dioxide emissions from different car types

Chart 2

Particulate matter is from exhausts, vehicle braking and tyres and is also emitted from burning of solid fuels both industrial (though this doesn’t contribute as much in areas of exposure to humans) and domestic wood burners – historically a very small factor but with the massive growth in wood burners it appears this could change.

In theory a modern, efficient, Defra-approved wood burning stove should not produce enough PM to be a health problem. However there are stoves that are not Defra approved, a temptation to burn waste wood including composite materials such as ply, MDF and chipboard, treated timber ( tantalised, varnished, painted etc) and unseasoned wood at more than 15% or even 20% moisture content, and all these things produce pollutants that can harm human health.

Fine Particles

PM 10 and PM 2.5 are classifications of different sizes of particle. Larger particles can be visible in the form of smoke; PM 10 and 2.5 refer to particles of equal to or less than this size in micrometres (0.001mm).

NO2 is completely invisible. PM 10 and PM 2.5 are invisible too. This can be a factor in society’s failure to date to address the problem.

Bristol City Council is concerned about both NO2 and PM. At the moment NO2 is the top priority for a number of reasons, not least the legal imperative.

Useful Links