When the prominent nitrophile Sunburst Lichen (Xanthoria parietina) is abundant on roadside trees and twigs next to busy main roads in English cities, what is the minimum NO2/NOx levels that make this possible?
In parts of NW England, such as Northenden, roadside trees of major highways are often plastered with bold colonies of Sunburst Lichen, a well-known nitrophile. In some instances, the colonies are large enough to be visible on Google Earth Street View.
The abundance of the nitrophile colonies invariably declines sharply away from the kerbside, and the colonies are generally rare or absent on roadside trees more than 100 metres away from the busy road. The limit of the nitrophile shows quite good spatial relationship to the computed boundaries of the Greater Manchester Air Quality Management Area (AQMA) that have been computed entirely from NO2 static diffusion tubes merged with traffic flow models.
So far, our team has found more than 20 urban shopping centres along busy roads have roadside trees with the Sunburst Lichen, such as Northenden, Wythenshaw, Chorlton, Stockport, Stretford etc. By this means we are achieving a much more detailed fact-based resolution of NOx polluted areas than possible with the AQMA, including in some instances intense hotspots at school gates and congested bus stops.
Therefore we are seeking experimental data on the NO2/NOx limits for abundant Xanthoria parietina as a simple indicator of levels of NO2/NOx.
Our fast-track method is yeilding good results and we are interested in linking with a) community-based mappers and b) scientists able to conduct experiments on Xanthoria parietina's NOx junkie-like distribution.
Robin Francis Grayson
Northenden, Manchester
I do not know the answer but this is a very interesting question. Perhaps co-locating passive NO2 samplers would shed some light on this?
Regarding NO2/NOx, until about last decade or so, NOx were mostly emitted as NO, with NO2 forming gradually in the air. Oxidation catalysts in many newer diesel engines cause the share of NO2 in NOx to be in tens of percent. Is the nitrophile abundance a recent observation, possibly correlated with increase in NO2/NOx ratio in emissions?
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