Air Quality Survey

On the 1st May we carried out our first Meadow air quality (lichen) survey, developed by the Natural History Museum as a country-wide OPAL initiative.

What is air pollution?

Much of the air pollution in Britain today is largely invisible and is difficult to detect, although you may be able to smell the pollutants from car exhausts, farmyards and heavy industry. These include ammonia and oxides of nitrogen. Although nitrogen is essential for the growth of all living organisms, too much nitrogen can cause problems.

So what it all has to do with lichens?

Nitrogen can stimulate the growth of some plants and fungi but stop others from developing. In our survey we were looking for lichens that are known to grow particularly well when they are close to sources of ammonia, as well as lichens that do not like excessive nitrogen in any form. Lichens are well known for their sensitivity to air pollution, which is why they are being used in our survey.

What are lichens?

Main kinds of lichen

Lichens are made up of two or more different organisms living together, a fungus and an alga. You can read a lot about them on the OPAL website.

What were we looking for?

We were looking for the nine most common types of lichen: three types which were indicators of very clear air; three types which were nitrogen loving and were indicators of the polluted air, and three types which can grow anywhere. You can find a nice guide here.

What did we find?

Nitrogen-loving Xanthoria

We found a lot of trees covered by nitrogen-loving species: Cushion Xanthoria, Leafy Xanthoria and Physcia. You can easily see them all over the Meadow, on tree trunks and lower branches.

Nitrogen-loving Physcia

We spent the whole morning doing detective work studying the lichens and after a considerable effort we found five samples of Evernia and one sample of Usnea (although we were not 100 % sure about the Usnea). They both are indicators of the clean air.

Clean air loving Evernia

We found them near the fish gate – the furthest corner away from A34! They grew on young branches, which mean that they were also young and that the air on the Meadow might be improving! We submitted our results into the national database and you can see our survey on their map, shown here.

What do our results mean?

Whitchurch air pollution score

Unfortunately, the air on the Meadow is not so clean. No surprises here: A34! The good news is that it might be improving: there were clean air lichens on very young branches. Maybe trees are getting bigger and screen the Meadow better from the A34. Maybe cars are getting cleaner. Maybe recession is kicking in and reduces traffic along the A34. We are not sure.

The pollution scale used by OPAL ranges from +54 (very clean air) to -54 (very polluted air).

The Meadow’s pollution score was calculated to be: -15! This was calculated using an average of all the trees we analysed on the Meadow.

What would we like to do next?

Meadow detectives investigating lichens

First of all, we would like to keep repeating the survey twice a year and record our results. This way we will be able to tell if the air is changing. Who knows, maybe in 20-30 years when we run out of oil, our grandchildren will be hunting that precious sample of bright yellow pollution-loving lichen which is so abundant on the Meadow now!

How can you help?

We have another idea you can help us with! Help us to plot the Whitchurch map of air pollution!

We would like to know: How far away from the A34 do you need to go to find clean air lichens?

Lichen pocket guide (Adobe Acrobat pdf)

Are you a keen walker? Print out the OPAL pocket guide to lichens (or contact us and we will get one to you) and then let us know where in Whitchurch (or surroundings) you can spot any of the three clean air lichens: Usnea, Evernia and Hypogymnia. The first two are easy to identify: they are sticking out of the branches. The last one is closely attached to the tree but should be easily recognisable by its puffed hollow lobes.