Diffusion Tube Data

Diffusion tubes are small, relatively inexpensive air pollution (nitrogen dioxide) monitors.  They are small plastic tubes, open at one end with a gauze at the other end.  The gauze is soaked in a chemical that captures the pollution and lets us work out the average amount of pollution in the air. This data has all of the monthly pollution levels measured in Calderdale using diffusion tubes since 1993.  The older measurements (1993-2003) were in “parts per billion”.  One part per billion means that in one cubic metre of air there was one cubic millimetre of pollution.  This unit can be converted to the one in use now, micrograms per cubic metre, by multiplying by 1.91.  More recent measurements are reported in these units. The diffusion tubes have been placed in many locations over the years, to investigate where the air pollution ‘hot spots’ might be, so the files may show different tubes for different years.  Most of the tube locations are shown on [Calderdale Maps Online](https://www.calderdale.gov.uk/v2/maps/environmental "Maps online").