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Data and Statistics

Welcome to the Welsh Air Quality Data and Statistics Database. These pages contain options for you to retrieve data relating to Air Quality in Wales from the present day back to 1986.

The database contains tables of measured concentration data and statistics from the air quality monitoring sites operated by the National Assembly for Wales and other members of the Welsh Air Quality Forum. Estimates of emissions - the amount of pollution produced by a range of activities can be obtained from the National Atmospheric Emissions Inventory (NAEI).This link opens in a new window

Emissions and concentration statistics shown in this database are National Statistics. National Statistics are produced to high professional standards set out in the National Statistics Code of Practice. They undergo regular quality assurance reviews to ensure that they meet customer needs. They are produced free from any political interference. Further National Statistics are available at from Defra's Environment Protection Statistics and Information Management Division (EPSIM) at http://www.defra.gov.uk/statistics/environment/This link opens in a new window

Monitoring data

Automatic Networks produce hourly pollutant concentrations, with data being collected from individual sites by dial-up modem. The data go back as far as 1986 at some sites. By clicking on the map on the homepage of this web site you can get detailed information for each site presently in operation.

Non-automatic Networks measure less frequently - either daily, weekly or monthly - and samples are collected by some physical means (such as diffusion tube or filter). These samples are then subjected to chemical analysis, and final pollutant concentrations calculated from these results.

Simple Statistics

A range of simple statistics are routinely calculated by the database for the automatic monitoring data each night. These include:

  • Daily mean, maximum and minimum values for all pollutants.
  • 8-hour running mean values for ozone and carbon monoxide.
  • Daily maximum 8-hour running means for ozone.
  • Running 24-hour means for PM10 particulate matter.

Data Output

There are three options for the output of your database download, according to the size of the data request. Small enquiries can be shown on your screen using minimum HTML, moderately sized enquiries can be e-mailed to you as an attachment in comma separated format, or the largest enquiries will be left on an ftp site, also in comma separated format, for you to collect. The data on the ftp site will be wiped within seven days if it is not retrieved.

The comma-separated format should make it easy to load the file into a spreadsheet once saved to your local machine. If the program does not recognise the format automatically, you will need to set the file type to "Text" and the separator as "Comma" for Lotus, or rename the file to [NAME].csv for Excel.

Data Verification and Ratification

A description of the data verification and ratification process can be found here.