Application of lichen-biomonitoring to assess spatial variability of urban air quality in Manchester, UK

Airborne pollutants are increasingly impacting on urban populations, contributing to acute and chronic human health issues, e.g. cardiovascular and lung diseases, leading to approximately 40,000 premature deaths within the UK. Within the City of Manchester, two automated monitoring stations record atmospheric pollutants (i.e. CO, SO2, NOx and PM), but do not record airborne metal and PAH concentrations and are restricted in number, thus only recording localised air quality. This necessitates the application of additional monitoring methods to assess spatial variability of air quality, i.e. using biomonitors and passive monitoring devices. Lichens are proven biomonitors for atmospheric pollution, due to their morphology, lacking roots, cuticle and stomata, and thus absorbing, adsorbing and accumulating nutrients and atmospheric pollutants within their biological tissue. The aim of the study was to document and assess spatial variability of air quality in the City of Manchester, by applying a high spatial resolution lichen biomonitoring approach. Xanthoria parietina and Physcia spp. lichens (N=94) were analysed for carbon, nitrogen and sulphur contents and their stable-isotope-ratio signatures (δ13C, δ15N and δ34S). Furthermore, a new method was developed to extract nitrate and ammonium from lichen material, to investigate relative importance of both compounds on bulk nitrogen and δ15N values. Airborne metal and polycyclic aromatic hydrocarbon concentrations were further analysed to investigate potential sources (i.e. vehicular emissions) and potential human health risks. Lichen chemical data, was in part, ground-truthed by NOx diffusion tube analysis for NO2 concentrations. Findings indicated the beneficial use of lichens to biomonitor air quality at a high spatial resolution. Elevated pollutant loadings in lichens illustrated deteriorated air quality in Manchester. However, a complex mixture of pollutants affecting air quality in Manchester were indicated, with regard to its urban layout (i.e. road network, traffic counts and building heights) and subsequent dispersion and distribution of pollutants. This work contributed to a better insight into the variability of urban air quality, which could then be applied to (comparable) urban environments. Moreover, a high spatial lichen biomonitoring approach can be used to investigate and identify areas of concern regarding human health risks.