Guide to Using a Lichen Based Index to Nitrogen Air Quality provides a simple method for determining gaseous nitrogen pollution that can be used by anyone interested in the impacts of gaseous N on sensitive habitats in the UK. It includes a simple identification key to epiphytic lichens growing on oak and birch that show sensitivity to, or tolerance of, atmospheric N pollution. The lichen species present at your location are used to calculate a lichen indicator score (LIS), which is then converted into a standardised nitrogen air quality index (NAQI), showing the nitrogen air quality at your location.