OPAL air survey resources

Introduction

The OPAL Air Survey allows participants to find out about the air quality in their local area and across the country, and discover how the natural environment is affected by air pollution. It uses ‘bioindicators’, species whose presence or performance is sensitive to changes in environmental conditions. The OPAL Air Survey contains two activities, using different bioindicators of air pollution.

Activity 1: Lichens on trees

The survey recorded the abundance of nine different types of lichen growing on trees. This provided a bioindicator system for nitrogenous air pollutants, by including lichens that are nitrogen-sensitive (declining where pollution is high), nitrogen-tolerant (increasing where pollution is high) or intermediate (no strong preference).

Activity 2: Tar spot fungus on Sycamore

The tar spot fungus is sensitive to sulphur dioxide (SO2) pollution, and is less common where levels are high. Even though SO₂ pollution has reduced over the past 50 years, recent observations suggest that tar spots are still less frequent closer to city centres. Activity 2 tested two hypotheses as to why this might be:

• Street cleaning in city centres removes fallen leaves, which are a source of the fungus that causes tar spot
• Other types of air pollution, particularly nitrogen dioxide (NO₂) from road traffic, reduce tar spot formation

Survey results

Over 5,980 survey responses were submitted for the Air Survey, including observations of lichens growing on over 15,000 trees and tar spots on over 24,000 Sycamore leaves.  These rich datasets have formed the basis of several academic analyses, some key findings of which are outlined below. The survey has now been completed and results can be accessed at https://www.imperial.ac.uk/opal/surveys/airsurvey/.

The resources can be used by students for fieldwork investigations and can be downloaded by clicking the icons below.