Carbon monoxide (CO) is a colourless, odourless gas. It is formed by the incomplete combustion of fossil fuels, with traffic emissions being the dominant source of this pollutant, accounting for 90% of all emissions. Concentrations are highest nearest the kerbside, with emissions being greatest at low speeds and when the engine is “cold“.

The Government has set an air quality objective for carbon monoxide to be achieved by December 2003. The objective is 10 parts per million (ppm), expressed as an eight hour running mean, which means that this objective applies to locations where people may be exposed for an eight-hour period. The latest research into the Borough’s air quality indicates that this standard is being met.

Nitrogen dioxide gas (NO2) is formed by the oxidation of nitric
oxide gas (NO). Nitric oxide (along with a little nitrogen dioxide) is formed at high temperatures during combustion processes, such as the burning of diesel or petrol in motor vehicles, or industrial processes, such as power generation.

In ambient air, nitric oxide is then oxidised to nitrogen dioxide by reaction with ground-level ozone (O3). Collectively nitric oxide and nitrogen dioxide are referred to as nitrogen oxides (NOx).

Within urban areas the major source of nitrogen oxides is road traffic, with concentrations being at their highest nearest the roadside on busy congested roads. Highest concentrations tend to occur either on cold calm days during winter, as the pollution is unable to disperse very readily, or during summer photochemical smog episodes (see Ozone below).

Most Air Quality Management Areas (AQMAs) declared within the UK are due to difficulties in meeting the annual average standard, including the four AQMAs declared in Barnsley.

As there is a time lag in the chemical reaction forming ozone, the highest concentrations can be downwind from urban areas, where nitrogen oxides are emitted, resulting in higher concentrations in suburban and rural locations, rather than in city centres.

If the weather remains hot and sunny for several days, this “photochemical smog” will persist, and be transported over long distances. The hot summer of 2003 showed an increase in ozone pollution, with sources as far away as continental Europe sometimes contributing to these photochemical smog episodes.

The primary particle fraction consists of particles emitted from vehicles (especially diesel engines), industry and also from solid fuel burning on domestic grates. Finally, there is the secondary particle fraction. This consists of particles, which have formed due to chemical reactions within the atmosphere, resulting in the formation of sulphate and nitrate particles. The relative concentrations of these three constituents can vary with the weather and the location. During 2003, PM10 concentrations increased significantly, both locally and nationally.

There are currently two air quality standards for PM10 particles. An annual average of 40 micrograms per cubic metre has been set, to be achieved by December 2004. In addition, a daily average has been set at 50 micrograms per cubic metre, also to be achieved by the end of December 2004. This standard allows up to thirty-five days per year for the daily standard to be breached.
 

A large amount of research has been carried out on the health impact of fine particles in recent years, and, in addition to the concerns regarding the PM10 fraction, attention is being given to smaller particle fractions. These can penetrate further into the lung. The very latest research is also looking at the numbers of these particles we inhale, along with the composition of these particles.

Besides health effects, PM10 particles are also linked with dirt and visibility problems.

There are several air quality standards for sulphur dioxide, the most stringent of these being a fifteen minute average of 100 parts per billion. This standard, which has to be achieved by December 2005, allows up to thirty-five exceedences of this fifteen-minute standard each year. The Council is looking very closely at those parts of the Borough, which are still affected by either industrial or domestic emissions, in order to ensure that this stringent standard is not being exceeded. Concentrations of this gas have fallen dramatically over the last few decades however, due to the passing of the Clean Air Acts, and the subsequent success of the Council’s smoke control programme.