This advisory document is intended to take ecologists (and air quality specialists) through the issues that they should consider in order to make an informed judgement as to the ecological effects of changes in pollution concentrations and deposition rates.

This advice aims to provide the reader with a consistent approach to understanding such effects, without prescribing the conclusion that should be drawn in any given situation. It does not set out definitive steps to be followed but is written to aid ecologists in making a balanced and informed judgement as to ‘risk’.