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ECN contributes to major review of air pollution

Environmental Change Network data feature in a major new review of transboundary air pollution in the UK and other parts of Europe.

The Review of Transboundary Air Pollution (RoTAP) concludes that the chemical climate of the UK has changed dramatically over the last 30 years, and continues to change as a consequence of UK and European policies to solve air pollution problems.

Overall, sulphur emissions and sulphur concentrations and the acidity of rainfall have declined greatly, and soils and freshwaters are slowly recovering.

Compilation of the RoTAP review, led by the NERC Centre for Ecology & Hydrology (CEH), involved 60 scientists and reviewers over three years, including ECN’s Coordinator, Don Monteith. Among the many sources of evidence considered are soil water chemistry data from three non-agricultural ECN terrestrial sites (Glensaugh and Sourhope in Scotland and Moor House in England), and ECN vegetation data.

Overall, sulphur emissions and sulphur concentrations and the acidity of rainfall have declined greatly, and soils and freshwaters are slowly recovering

The soil chemistry data presented for the two Scottish sites show similar trends, with a marked decrease in acidic sulphate concentrations since 1993. Both sites show clear evidence of reduced acidity and therefore recovery in mineral soil horizons, but no overall change in the (more acid) organic horizons, consistent with data from other sources and locations.

Data from Moor House also indicate a recovery from acidity, but in this case there has been no change in either sulphate or nitrate concentrations in soil waters. Instead, the Moor House data suggest that human-produced hydrogen chloride (HCl) is the main acidifying pollutant involved. Most HCl is deposited close to source (mainly coal-burning power stations) and the potential for longer range transport of this pollutant has been rather overlooked (a separate paper by Chris Evans and colleagues addresses this topic). The gradual decrease in acidity at Moor House may be mainly due to a reduction in UK hydrogen chloride emissions, which declined by 94% between 1990 and 2006.

The co-location of measurements at ECN sites allows direct comparisons to be made between air pollution drivers and biogeochemical and ecological responses

In relation to nitrogen deposition, the RoTAP report draws upon evidence from ECN vegetation monitoring, which indicates only limited change in plant species composition over the last 10-20 years, consistent with data from other sources. Nitrogen is a major plant nutrient and increasing nitrogen deposition is expected to change species composition, and may reduce species richness, by favouring  those species adapted to quick exploitation of additional nitrogen. Nitrogen is deposited on vegetation and soils in a wide variety of forms (e.g. as ammonia, nitric acid and nitrogen dioxide) and as both ‘dry’ (gaseous form) and ‘wet’ (dissolved in precipitation) deposition. The total deposition of nitrogen has changed little over the period 1987 to 2006.

In compiling the RoTAP report, the authors reviewed a wide range of spatial and temporal physical, biogeochemical and ecological datasets in order to describe the current status of air quality and recent trends. While relatively small in number, the co-location of measurements at ECN sites allows direct comparisons to be made between air pollution drivers and biogeochemical and ecological responses, and thus provides a unique contribution to the wider national evidence base.

 

Further information

  • The Review of Transboundary Air Pollution was published in June. Download the RoTAP report here.
  • The RoTAP project was funded by the Department for Environment, Food and Rural Affairs (Defra), the Natural Environment Research Council (NERC) and the UK’s Devolved Administrations.  The latest report is the first detailed analysis since 2001, and shows the effects of policies introduced throughout Europe to mitigate long range transport of pollutants in Europe.
  • For more concerning hydrochloric acid impacts on soils see Evans, C.D., et al. (2011). Hydrochloric Acid: An Overlooked Driver of Environmental Change. Environ. Sci. Technol. 45(5), pp 1887–1894. DOI: 10.1021/es103574u
  • Using ECN’s Time Series Viewer it is possible to look at trends in parameters such as sulphate concentration and pH at terrestrial sites. Select ‘Chemistry: Soil solution’ (shallow or deep samplers).
  • Details of what we measure at ECN sites, and the methods used can be found in the Measurements section.

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