Researchers study the effects of air pollution on European ecosystems
Rising air pollution has been a concern for governments, business and environment campaigners for some time. Until very recently, little attention was given to the accelerator effects of climate change on nitrogen and ozone air pollution, and their consequences for Europe's ecosystems.
The European Union (EU)-funded research project ECLAIRE seeks to better understand these effects, which may both alter the air pollution threat and entail feedbacks that increase greenhouse gas emissions.
“Europe's ecosystems are under significant threat from nitrogen and ozone air pollution,” says project coordinator Mark Sutton of United Kingdom’s Natural Environment Research Council. “The emerging message of ECLAIRE is that climate change is likely to increase agricultural and biogenic air pollution, contributing to higher emissions of ammonia and volatile organic compounds in particular. These changes are likely to make mitigation actions under revision of the National Emissions Ceilings Directive even more important if the air pollution threat to natural habitats across the EU is to be reduced.” he adds.
The ECLAIRE team is investigating those implications at a number of European sites, both natural habitats and agricultural areas. Using a combination of field observations, experimental data and sophisticated modelling, the project team is examining the links between the strength of air pollution and likely effects on the ecological habitat.
The researchers are examining two pollutants in particular. The first one is nitrogen (N), a chemical element that makes up around 78% of the planet's atmosphere, but which also exists in several pollution forms, such as nitrogen oxides (NOx) and ammonia (NH3). In excessive amounts these affect plant competition, so threatening Europe’s native ecosystems. The second one is ozone (O3), which is formed from a cocktail of NOx and volatile organic compounds. Ozone is highly reactive and affects both natural and agricultural ecosystems, significantly crop production.
Field measurements are being carried out at locations with widely differing local environments across Europe. Sites are located, for example, near Edinburgh in Scotland, the surroundings of Paris, Bosco Fontana near Mantova in Italy, Speuld near Utrecht in the Netherlands, Brandbjergin in Denmark, and near Odessa in the Ukraine.
Taking the Bosco Fontana mixed oak forest near Mantova in Italy's Po Valley as an example, the ECLAIRE team is investigating in detail the effects of air pollution on the site, which is part of a heavily industrialised region – contributing high NOx emissions – as well as hosting intensive agriculture – contributing high NH3 emissions. The researchers have identified how chemical conversions in the forest canopy process this air pollution cocktail, enhancing the formation of fine particulate matter in the air (PM2.5) that also threatens human health. Together with on-the-ground measurements across the Po Valley, they have been building up a picture to increasing ly verify new methods for satellites to monitor these air pollution levels.
With the information from such field measurements, the ECLAIRE team is then modelling past and expected future changes in local climates for the period 1900–2050, and their likely impact on European forests and other ecosystems.
Now halfway through its term, the project has already produced some interesting results. The discovery of microscopic aerosol-particle uptake into the pores of leaves, for example, has ended a 40-year-old paradigm. “Our existing understanding of clean, hydrophobic (repelling water) leaf surfaces supported the fact that absorption of water into plant leaves was impossible due to water surface tension,” explains Sutton. “However, actual leaves are not clean – pollutant deposits on their surfaces can change leaf hydrophobicity – and since such deposits are always present and accumulate, plants can absorb waterborne pollutants this way,” he says, explaining that this effect can actually induce drought effects in plants as they are less able to reduce water loss in dry polluted conditions.
Critically, ECLAIRE's research team has also presented the important initial hypothesis, that climate warming is likely to worsen the threat of airborne pollutants to Europe’s ecosystems. Sutton explains: “Under warmer conditions gases are less soluble. The result is that the air pollutants like NH3 and volatile organic compounds are emitted in even larger amounts from agricultural and forest systems. These larger emissions mean that it will be even more important for Europe to take action to reduce emissions of these gases if the pollution threat to Europe’s Natura 2000 network is to be reduced.” These results are highly relevant as Member States now begin to consider the Commission’s proposals for revision of the National Emissions Ceilings Directive.
ECLAIRE researchers stress that the full quantitative analysis of the interaction between mitigation and adaptation measures has yet to be completed. However, the findings so far highlight the need for action to cut air-pollution emissions to avoid a further potential worsening of the air-pollution threat to Europe’s ecosystems.