Air quality

About this service

Clean air is essential for our health and quality of life. People expect that the air they breathe will not harm them. Although air quality in the UK is generally good, unacceptable levels of pollution are known to exist in some areas. Wiltshire Council has a statutory duty under the 1995 Environment Act to review and assess air quality within the county.

The Environment Act 1995 places responsibilities on local authorities to measure and manage air quality. This Act, and the National Air Quality Strategy, has set health-based standards for the seven main pollutants in the UK. They also set specific dates by which those standards must be met.

Some of the areas of work that we cover can be found here:

Frequently asked questions

If you have any concerns about Air Quality please contact us.

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North

View the Statement on the air quality situation in North Wiltshire, last assessed in the year 2000, in accordance with the National Air Quality Strategy, and confirms that there is no requirement to designate an Air Quality Management Area in North Wiltshire. Please click on the following links to view the various main sections of the report:

Updating and Screening Assessment Report

You will need Adobe Acrobat Reader to view the PDF documents on this page, which is available as a free download.

Please click on the following link to access the Updating and Screening Assessment Report.

Please click on the following links to access the progress reports on the review and assessment of Air Quality in North Wiltshire:

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South

In April 2006 we completed a detailed assessment report on Air quality in Salisbury.

This work resulted in the need to declare revised air quality management in the area which covers the whole city centre and two air quality management areas on London Road (A30) and Wilton Road (A36). These were made because of excessive levels of nitrogen dioxide in these areas.

We have now gone on to quantify the level of the problem in even more detail in a further Local air quality management assessment (2007) 5mb which looks at the types of vehicles that cause the greatest problem and how much pollutant levels must be reduced by in order to comply with air quality objectives set down in law.

For the latest annual report download the Air Quality Progress Report 2008.

Air quality trends at a glance

Below are links to graphs of nitrogen dioxide levels for the main areas we are keeping a watch on. The graphs represent the annual (12 month) average level of nitrogen dioxide. Nationally, it is proving the most difficult objective to meet. There is also short-term limit (15 minute average), which Salisbury easily achieves.

Notice the peak on each of the graphs for 2003. This was a brilliant hot summer but nationally bad for pollution levels. Also notice the drop in levels on Wilton Road. This was when Skewbridge was being rebuilt. There was a big drop in traffic and consequently a big drop in nitrogen dioxide.

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East

Air quality affects us all and is given a high priority by the Council.

Our Environmental Protection Officer completes an annual Air Quality Report for submission to the government.

Local Air Quality Management Report - Shanes Castle, Devizes - Sept 2009

Air Quality Annual Report 2007

To help with the completion of the report, we carry out monitoring of Nitrogen Dioxide levels at 25 sites across the East Wiltshire area. Monitoring has been carried out since 1994 and monitoring results are available on request.

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West

Monitoring for nitrogen dioxide using diffusion tubes has been undertaken at various locations within West Wiltshire for a number of years. The Government and the devolved administrations have adopted an annual mean Air Quality Objective for nitrogen dioxide of 40µg/m3.

Use of nitrogen dioxide passive diffusion tubes

Passive diffusion tubes are not as accurate as real time monitoring, however they do give a good indication of what is happening with air quality.

West Wiltshire currently has 11 sites within the county to monitor for nitrogen dioxide. Five of these sites are outside Air Quality Management Areas (AQMAs) and six are within an AQMA. View map of location sites.

A nitrogen dioxide passive diffusion tube is a clear plastic tube open at one end and at the closed end a mesh is impregnated with a pollutant absorbing chemical. The diffusion tube collects the pollutant during the exposure period and then is resealed and returned to a laboratory for analysis. Each tube is exposed for a period of a month. The laboratory then assesses the quantity of the pollutant absorbed by calculating the average ambient NO2 concentration over the exposure period.

Each tube is mounted on a lamp-post or similar structure ensuring that the open end is at the bottom to prevent rainwater collection.

Photo of diffusion tube in use

West Wiltshire utilises diffusion tubes prepared and analysed by Bristol City Scientific Services. The laboratory participates in the Workplace Analysis Scheme for Proficiency (WASP) for nitrogen dioxide tubes.

They analyse a solution supplied by Netcen as part of the QA/QC scheme that they run.

The laboratory also participates in a field inter-comparison scheme which is controlled by Netcen and organised by the Health and Safety Laboratory. Three tubes are co-located with a continuous analyser which provides a reference value.

The tubes are prepared by pipetting 30l of solution of 20% triethanolamine in water onto the metal grids in the end of the cap, then assembling the tube components. A fresh batch of tubes is prepared each month ready to dispatch in time for the required exposure date.

Laboratory blanks are retained so that at least one is run alongside each batch of samples. Travel blanks are supplied every three months as required by the UK survey procedure.

Below are the nitrogen dioxide diffusion tube annual average results expressed in µg/m3 since 2000 and the results from the automatic analyser for nitrogen dioxide located in St Margarets Street, Bradford On Avon.

Bradford On Avon site locations 2002 - 2007, corrected annual average data of nitrogen dioxide from diffuion tubes (µg/m3)

Note: Government target levels for Nitrogen Dioxide is an annual average of 40µg/m3

Location 2002 2003 2004 2005 2006 2007
Masons Lane 58 59 59 59 66 53
Silver Street - 36 34 35 36 31
New Road - 25 22 25 23 19
St Margaret's St 1 - 33 31 30 30 27
St Margaret's St 2 - 35 32 29 32 27
St Margaret's St 3 - 32 31 30 31 27

Bradford On Avon automatic site location 2004 - 2007, annual average data of nitrogen dioxide (µg/m3)

 2004 2005 2006 2007
St Margarets Street 27 28 29 26

Bradford On Avon site locations 2007, corrected monthly data of nitrogen dioxide from diffuion tubes (µg/m3). West Wiltshire bias correction factor of 0.68 used

Note: Government target levels for Nitrogen Dioxide is an annual average of 40µg/m3

Site Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
BOA 9 Masons Lane 50 48 51 60 52 51 53 40 53 55 66 56
BOA St Margaret C/L 27 26 26 22 25 23 24 25 28 32 29
BOA St Margaret C/L 27 26 26 24 26 22 24 26 27 34 27
BOA St Margaret C/L 27 28 27 26 23 28 22 25 25 28 33 28
BOA Silver Street 33 31 34 27 26 26 31 30 31 36 0
BOA New Road 20 20 19 16 15 15 0 18 0 18 26 26
BOA Rear of 9 Masons Lane 16 20 16 13 10 11 8 11 14 16 22 20

Westbury site locations 2007, corrected monthly data of nitrogen dioxide from diffuion tubes (µg/m3). West Wiltshire bias correction factor of 0.68 used

Note: Government target levels for Nitrogen Dioxide is an annual average of 40µg/m3

Location Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Warminster Road - post 76 28 35 31 39 29 35 29 36 33 40 43 37
Warminster Road - post 90 39 45 39 53 23 48 38 39 42 53 51 56
Haynes Road 28 35 40 56 31 38 26 41 44 16 24 19
Danvers Way 13 15 12 0 8 7 0 0 12 0 19 16
Oldfield Park 12 17 14 16 0 8 13 0 13 51 52 37
Oldfield Road 18 22 19 19 15 17 0 0 0 0 0 0

Trowbridge site locations 2007, corrected monthly data of nitrogen dioxide from diffuion tubes (µg/m3). West Wiltshire bias correction factor of 0.68 used

Note: Government target levels for Nitrogen Dioxide is an annual average of 40µg/m3

Location Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
County Way, Trowbridge 27 29 28 29 20 29 25 27 27 34 37 36
Hill Street, Trowbridge 21 34 24 27 23 27 22 26 26 30 36 34

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Last updated: 3 February 2010