NO2 Diffusion Tube Monitoring Calendar

Change Over Dates 2025

Suggested Exposure Periods (2025)
Period	Start Date	End Date	Duration (weeks)
January	8 January	5 February	4
February	5 February	5 March	4
March	5 March	2 April	4
April	2 April	30 April	4
May	30 April	4 June	5
June	4 June	2 July	4
July	2 July	6 August	5
August	6 August	3 September	4
September	3 September	1 October	4
October	1 October	5 November	5
November	5 November	3 December	4
December	3 December	7 January	5

The start and end dates of the exposure months are on Wednesdays and exposure periods still consist of 4 or 5 whole weeks, i.e. 28 or 35 days.
Tubes should be changed on the specified date. If not tubes may be changed within ±2 days of the due date.
The Diffusion Tube Data Processing Tool has been developed to assist local authorities in processing their NO₂ diffusion tube monitoring data. The outputs of this tool can be directly uploaded into Diffusion Tube Data Entry System (English local authorities, Scotland and Wales).
The Diffusion Tube Data Processing Tool can accept data from exposure periods other than those above, but data will not be eligible for inclusion in the Air Quality Archive.
Please keep a record of site irregularities that may occur in monitoring, for example, building work, changes in traffic flow, etc. This information may be helpful in explaining any unusual results.
For a PDF copy of the current calendar, please contact the LAQM Helpdesk.

Suggested Exposure Periods (2024)
Period	Start Date	End Date	Duration (weeks)
January	3 January	31 January	4
February	31 January	6 March	5
March	6 March	3 April	4
April	3 April	1 May	4
May	1 May	5 June	5
June	5 June	3 July	4
July	3 July	31 July	4
August	31 July	4 September	5
September	4 September	2 October	4
October	2 October	6 November	5
November	6 November	4 December	4
December	4 December	8 January	5

For older versions of the Diffusion Tube Monitoring Calendar please contact the LAQM Helpdesk for further assistance.

Cookie	Duration	Description
_ga	2 years	The _ga cookie, installed by Google Analytics, calculates visitor, session and campaign data and also keeps track of site usage for the site's analytics report. The cookie stores information anonymously and assigns a randomly generated number to recognize unique visitors.
_gat_UA-28909098-1	1 minute	A variation of the _gat cookie set by Google Analytics and Google Tag Manager to allow website owners to track visitor behaviour and measure site performance. The pattern element in the name contains the unique identity number of the account or website it relates to.
_gat_UA-6712674-5	1 minute	A variation of the _gat cookie set by Google Analytics and Google Tag Manager to allow website owners to track visitor behaviour and measure site performance. The pattern element in the name contains the unique identity number of the account or website it relates to.
_gid	1 day	Installed by Google Analytics, _gid cookie stores information on how visitors use a website, while also creating an analytics report of the website's performance. Some of the data that are collected include the number of visitors, their source, and the pages they visit anonymously.