Impacts Of Vehicle Emissions on Vegetation

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Pollutants derived from vehicle emissions now pose a major threat to human health and urban ecology. This project aims to evaluate the impacts of urban pollutants on vegetation, water relations and plant-insect interactions to provide generic information for future remediation and conservation of vegetation in urban areas. Specifically the project aims to:

  • evaluate the impacts of urban air pollution climates on a range of plant species and their insect herbivores using a combination of roadside transects and controlled exposure studies
  • study the effects of these pollutants on leaf function and enzyme activities
  • determine the effects of these pollutants on leaf chemistry and plant-herbivore interactions
  • identify the relative importance of different components of urban air pollution in adversely affecting plants and their insect herbivores
  • evaluate the importance of vehicle pollutants as a limiting factor for lichen recolonisation of urban areas
  • identify and characterise the abiotic stresses in the urban plant environment that affect growth, and the uptake and response to air pollutants
  • derive initial estimates of critical levels of pollutant mixtures for urban ecosystems
  • identify which types of plant species are tolerant of urban pollution climates




The project will use both in situ and controlled environment experiments. It will evaluate impacts on a range of vegetation of contrasting morphologies and functional types. The controlled experiments will be conducted in the Solardome exposure system developed in a previous URGENT feasibility study. The in situ experiments will be carried out at sites in Newcastle, Manchester and Central London.

The Newcastle In Situ Studies - effects of urban pollutants on urban shrubs

Transects will be set up on a major road/open parkland interface near the University where traffic densities and pollutants are monitored. Insecticides will be used to manipulate effects of hervibory on established vegetation. Impacts of pollution atmospheres on leaf surfaces, growth and physiological processes will be assessed.

Imperial College experiments in the Natural History Museum Wildlife Garden

This group will examine the effects of urban pollutants on herbaceous plant species. Transects will be set up within the established wildlife garden and pots of other herbaceous plants will be added. A range of plant growth and physiological factors will be monitored. The effects of artificially increased daylength through street lighting will be assessed

Manchester in Situ Studies - effects of urban pollutants on trees

This study will investigate the health of plants along existing gradients. Plant growth and physiological aspects will be monitored.

Bradford University effects on lichens and bryophytes

Impacts of vehicle pollutants, directly or indirectly via changes in bark chemistry, will be assessed by transplanting lichen and bryophyte species from relatively unpolluted sites in North Wales to the Solardomes and field sites of other collaborators.

Solardome Experiments

The Solardome provides realistic urban atmospheres, including VOCs and particulates. A range of species, including those in the field based trials will be exposed in the Solardome. Impacts of pollution treatments will be measured including visible injury, leaf canopy development and turnover, rates of photosynthesis and stomatal conductance. The Solardomes will be used to conduct controlled complementary studies to confirm in situ effects from the field monitoring and experiments.

Start date/duration

October 1999 Three years

Lead Organisations

CEH Bangor

University of Newcastle

Imperial College London

CEH Pencuik

University of Bradford

Manchester Metropolitan University


All experimental data will be placed on an Oracle based Integrated Data System to facilitate access and transfer to other users. The project will bring the following benefits/deliverables:

  • Identification of tolerant plant species for urban planting programmes
  • Identification of risks to urban vegetation from invertebrate attack and influencing factors
  • Development of bio-indicators of exhaust-related emissions for widespread use in cities, for spatial and temporal monitoring
  • Initial estimates of critical levels of pollutants for urban areas
  • Better understanding of the exchange of VOCs and deposition of particulates to foliage
  • Better understanding of pest/host relationships in perturbed environments
  • Pointers to future research areas (e.g. into individual components of vehicle emission control (as affecting urban vegetation/air)


Local Authorities


English Nature

Countryside Council for Wales

Welsh Office

Further details

Further information is available from the following contacts:

Lead Researcher: Professor T.W. Ashenden

Tel: 01248 370045, Fax: 01248 355365, email:

URGENT Programme Manager: Graham Leeks

Tel: 01491 692203, Fax: 01491 692313, e-mail: