Citizen science identifies the effects of nitrogen dioxide and other environmental drivers on tar spot of sycamore

Laura Gosling, Mike Ashmore*, Tim Sparks, Nigel Bell

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Elevated sulphur dioxide (SO2) concentrations were the major cause of the absence of symptoms of tar spot (Rhytisma acerinum) of sycamore (Acer pseudoplatanus), in urban areas in the 1970s. The subsequent large decline in SO2 concentrations has not always been accompanied by increased tar spot symptoms, for reasons that have remained unresolved. We used a large citizen science survey, providing over 1000 records across England, to test two competing hypotheses proposed in earlier studies. We were able to demonstrate the validity of both hypotheses; tar spot symptoms were reduced where there were fewer fallen leaves as a source of inoculum, and elevated nitrogen dioxide concentrations reduced tar spot symptoms above a threshold concentration of about 20 μg m-3. Symptom severity was also lower at sites with higher temperature and lower rainfall. Our findings demonstrate the power of citizen science to resolve competing hypotheses about the impacts of air pollution and other environmental drivers.

Original languageEnglish
Pages (from-to)549-555
Number of pages7
JournalEnvironmental Pollution
Early online date29 Apr 2016
Publication statusPublished - 1 Jul 2016

Bibliographical note

© 2016, The Author(s).


  • Acer pseudoplatanus
  • Citizen science
  • Nitrogen dioxide
  • Rhytisma acerinum
  • Tar spot

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