Currently Bath and North East Somerset Council operates a number different monitoring sites looking at the following pollutants:


Benzene (C6H6) is a complex compound of carbon and hydrogen which is a liquid at room temperature but which readily evaporates to emit small amounts into the atmosphere.

BAM Tape

Any Benzene found at ground level is almost certainly a result of human activity. Benzene is gradually broken down in the atmosphere but this will take several days.

Benzene is a recognised human carcinogen that attacks the genetic make up of tissue cells. Those exposed to high levels of Benzene have a greater risk of developing certain types of cancer and leukaemia.

In Bath & North East Somerset benzene concentrations are measured at 1 site on the London Road in Bath. This is a pumped benzene analyser that is part of the national non-automatic hydrocarbon network, installed in 2008. At all times the concentrations have been lower than the Government objective of 5 micrograms per cubic metre (µg/m3).

Carbon Monoxide

Carbon monoxide (CO) is a very dangerous pollutant gas causing death in very high concentrations. It is colourless, tasteless and has no smell.

Carbon Monoxide is produced in the process of combustion, complete combustion in the presence of oxygen produces carbon dioxide (CO2) but if there is a deficiency of oxygen carbon monoxide is produced. Almost all combustion produces some carbon monoxide, the amount depending on the efficiency of the process and the availability and access of oxygen.

The main sources of carbon monoxide are vehicle emissions and the burning of fossil fuels. The emission of carbon monoxide from vehicles is at its highest at low speeds, therefore the peak values are recorded during the morning and evening rush hour periods.

Carbon Monoxide interferes with the red bloods cells ability to transport oxygen around the body, at high concentrations the effect on the body is severe resulting in loss of consciousness and even death. Those with existing heart problems are particularly at risk.

Carbon Monoxide is no longer monitored in Bath & North East Somerset, as the levels are significantly below the national objective limit. The reduction in levels is due to improving fuel and engine technology.

Nitrogen Dioxide

Nitrogen dioxide (NO2) is one of the most dangerous of the oxides of nitrogen to human health. It is released directly into the environment or formed by the conversion of nitric oxide (NO) in oxygen or ozone. The biggest contributions to nitrogen dioxide levels in the UK are from motor vehicles, electrical supply industry and the industrial and commercial sectors. Domestic heating also forms a significant source in urban areas.

In general the levels of Nitrogen dioxide peak in urban areas during the two rush hour periods of the day. The greatest levels are generally on cold days with low wind speeds when a blanket of cold air traps the nitrogen dioxide at ground level, allowing levels to build.

Nitrogen Dioxide has shown to be an irritant with the ability to increase sensitivity to allergens at high levels. There is evidence that exposure can increase the risk to children of respiratory infections and cause impairment of lung functions in later life. 

NO2 diffusion tube on a lamppost in Odd Down, Bath

Asthmatics and those suffering from emphysema and other breathing problems are thought to be especially sensitive to the levels of Nitrogen Dioxide.

In Bath and North East Somerset two methods of Nitrogen Dioxide measuring are used. The first is diffusion tubes which consist of open tubes with a pollutant absorbing gel at one end. The relative cheapness of this method allows for sampling at a large number of sites - currently about 100 in Bath & North East Somerset. The tubes can be used to measure the average levels of pollutants but are unable to measure peak values. The second measurements are done using continuous analysers which measure the oxides of nitrogen using chemi-luminescence. Four of these analysers are located at London Road (2), Windsor Bridge and the Guildhall.


Ozone (O3) is a very reactive chemical formed by the reaction of nitrogen dioxide and sunlight. The formation of ozone in the atmosphere is also contributed to by the presence of Volatile Organic Compounds (VOC).

Ozone is removed at night and inside buildings by reactions with surfaces. Ozone is found in lowest concentrations next to busy roads where to the release of nitric oxide (NO) from vehicles are highest. Nitric oxide reacts with ozone and removes it from the atmosphere. The highest concentrations of ozone occur during the summer months when sunlight is at its strongest in rural areas where there is little nitric oxide from vehicles to remove the ozone.

High concentrations of ozone at ground level can irritate the delicate surface tissues of the body, including lungs, eyes and nose.

Ozone is monitored using 2 indicative mobile monitors that are lamp-post mounted.

Particles (PM10)

Particles are a mixture of organic and inorganic matter. The size of the particle determines the time it remains in the air and it interaction with humans. Particles above a diameter of 10 micrometres (µm) will be trapped by the nose and pharynx whilst those smaller will be able to penetrate the lung and alveoli. For this reason the monitoring of particles usually concentrates on the particles likely to be deposited in the lungs, referred to as PM10.

Particles are derived from a number of sources. Primary particles are those emitted directly into the atmosphere (such as in vehicle exhaust). Secondary particles are formed by chemical reactions

Some are released directly into the environment by power stations, factories and motor vehicles. Vehicles contribute approximately 25% of particle emissions across the UK but this figure is thought to be much higher in urban areas. 

Monitoring enclosure at Lower Bristol Road nr Windsor Bridge

Of this 25% Diesel vehicles are responsible for 19%. Other sources of particles include those formed as sulphates and nitrates from Sulphur Dioxide and Nitrogen Dioxide and natural particles from spores and grains of pollen.

Particles are implicated in the increase of airway obstruction and underlying lung disease conditions. Also some particles (including hydrocarbons) may be carcinogenic.

There are two sites in Bath & North East Somerset where PM10 measurements take place. They are located at Windsor Bridge and at an enclosure on London Road and use a BAM 1020 to take the readings.


Pollen is a grain released from a plant to transport the male gamete to the female part of a plant.  1 in 5 of the population are allergic to these grains and suffer with a condition called Hay Fever.  Further information is available on our Pollen Monitoring webpage.


Smoke is defined as a suspension of particles less than 5µm in diameter. Smoke can act as a carrier for other gaseous or liquid pollutants and can cause ill health especially when in combination with sulphur dioxide.

The highest levels of smoke are generally found during the winter months due to an increase in the burning of bonfires especially around Guy Fawkes night.

Monitoring of smoke and black carbon were carried out at Bathwick Street in Bath until 2011.

The city of Bath is a Smoke Control Area.  Smoke must not be discharged from domestic chimneys.  Further information is available on our Smoke Control webpage.

Sulphur Dioxide

Sulphur dioxide (SO2) is one of the pollutants that led to the introduction of atmospheric pollution legislation. The main pollutant responsible for acid rain sulphur dioxide dissolves easily in water to form Sulphuric acid.

The main source of sulphur dioxide is the burning of fossil fuels in power stations and refineries. The use of coal as a domestic fuel is also a significant source. 

Sulphur dioxide is bronchoconstrictor causing a narrowing of the airways. Asthmatics are more sensitive to Sulphur dioxide than most others although at high concentrations it acts as an irritant and provokes wheezing.

Monitoring of Sulphur dioxide was carried out in Bath and North East Somerset at the Guildhall in Bath until December 2007.  All monitoring data was lower than the Government's Objectives.

Monitoring Sites

The council operates seven continuous monitoring sites providing up to date information on various pollutants.

  • London Road*- nitrogen dioxide and benzene
  • London Road Enclosure - particulates (PM10) and nitrogen dioxide
  • Guildhall - nitrogen dioxide
  • Lower Bristol Road nr Windsor Bridge - nitrogen dioxide and particulates (PM10)
  • Bathwick Street - nitrogen dioxide, nitric oxide and ozone (indicative)
  • Dorchester Street - nitrogen dioxide, nitric oxide and ozone (indicative)

* For up to date monitoring information from the UK Air Quality Archive visit their website at  http://uk-air.defra.gov.uk.

There is also a network of diffusion tubes covering background and roadside locations in Bath and North East Somerset.  These are collected monthly and provide annual mean concentrations of Nitrogen Dioxide.

Help us improve our website

Help us understand how people group our service.

Take part

Become a website tester

If you would like to be contacted by a member of our team to help us understand how people use our website please leave your details below.


To prevent automated spam submissions leave this field empty.

Your rating: 

Your rating: None Average: 2 (5 votes)
To prevent automated spam submissions leave this field empty.