OPAL Air Survey analysis

What have you helped us to find out about lichens so far?

In 2013, OPAL scientists* published an article in the scientific journal Environmental Pollution which looked at the results from the lichen activity in the OPAL Air Survey and investigated the link between lichens and air pollution.

Lichen expert Pat Wolseley and OPAL data manager Laura Gosling explain the science behind that article and what your hard work has helped us to discover.

Pat Wolseley at the air survey launch

Our methods

To examine the effect that air pollution has on lichens, the OPAL scientists* used lichen data submitted between August 2009 and September 2011.

You contributed a total of 4,093 surveys on 13 different deciduous tree species.

The tree sampled most often was Oak, where 1,456 surveys were carried out. We wanted to compare results from the same tree species across the country (because lichens are sensitive to different bark types from different tree species) so we first analysed the results from Oak trees. 

Data about lichen frequency on Oak trees was compared with air pollution maps using a 5km grid across the UK. These maps were made from modelled data, meaning that because air pollution sensors are not present in every 5km grid square, the data in between is estimated using a range of computer methods and climate data.

Different types of air pollution were investigated, including two different types of nitrogen pollution; ammonia from agricultural sources and oxides of nitrogen from car exhausts and industry. 

A value, or index, was given to each grid square, based on the amount of nitrogen-sensitive lichens minus the amount nitrogen-loving lichens, so squares with a negative value have mainly nitrogen-loving lichens and squares with a positive value have mainly nitrogen-sensitive lichens.

The lichen data was also compared with maps for climatic conditions of humidity, precipitation and average annual temperature.

The results

So now you know how we analysed your data. But what did all this modelling and mapping reveal?

Notes:

  • *The OPAL Scientists are the authors of the article.
  • The full reference for the article is as follows: Seed, Lindsay; Wolseley, Pat; Gosling, Laura; Davies, Linda; Power, Sally (2013): Modelling relationships between lichen bioindicators, air quality and climate on a national scale: results from the UK OPAL Air Survey. Environmental Pollution, 182:437–47.

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