Guide to using a lichen-based index to nitrogen air quality

Reactive nitrogen in the atmosphere is a threat to the condition and integrity of many sensitive habitats, potentially altering the competitive balance between different species.

The regulatory authorities, as part of their duties, have to consider the adverse effects of such pollutants on ecological biodiversity and to take cognisance of these effects. The current policy assessment of nitrogen impacts at a UKscale uses the critical loads and levels approach. However, it is recognised that the critical loads/levels approach is limited and does not make a direct link to site condition.   In order to quantify the nitrogen threat more effectively and support decision making, robust bio-monitoring methods are needed that can provide an appropriate evidence base.

The key objective of this project was to further develop and improve the methodologies for using lichens and other epiphytic species as indicators for assessing reactive atmospheric nitrogen (N) impacts at designated sites and semi-natural/natural habitats.  

This was achieved principally through: 

  • expanding and further developing the nitrophile (nitrogen tolerant)-nitrophobe (nitrogen sensitive) methodology, particularly through the use of lichens that are prevalent across a range of habitat types and present on a range of surfaces found in a rural setting, into a field guide;
  • improving the identification of which lichen species are sensitive; and
  • testing the finalised methodology through field trials.

The primary output of this project, a laminated field guide, will enable specialists and non-specialists to determine air quality, with respect to nitrogen (N) pollution by using common lichen to calculate an air quality index for a site. This information will tell you the relative health of your site and its risk of being compromised by N air pollution.

Copies of the field guide can be ordered from the Field Studies Council (FSC) for £3 plus postage. However, staff working for the organisations who participated in this project may be able to acquire a copy internally.


The research on which this fully developed methodology is based and supported is captured in two data reports, as well as – at least in part – in the PhD thesis of the student who undertook much of the research. You can access the thesis at The two supporting data reports, as well as a low-resolution version of the field guide, can be downloaded from this project page.

The information supporting the protocols that underpin this guide, as well as recording sheets for use in the field, can be found in the associated field manual at The field manual will be revised and augmented as required in response to use of the field guide.

Add This sharing button

Sign up to our ebulletin

Get email updates from Sniffer delivered straight to your inbox.

* means a required field.