Monitoring atmospheric composition & climate
Poor air quality over north-west Europe

ENS_pm2p5_2014040300_SFC_010_small.pngThe United Kingdom and the Netherlands have been confronted this week by poor air quality. Forecasts from the UK Met Office and DEFRA showed high levels of pollution for most of the week, which were confirmed by observations, especially today in the London area. MACC-II has been following the developments closely, analysing its own global and European forecasts.

While the media coverage in the UK focused significantly on the flow of Saharan desert dust over Europe, the MACC-II analysis provides a more complicated picture. The global forecasts show indeed plumes of desert dust moving all the way to the UK and the Benelux, but this is quite normal for the time of the year. The dust is visible as a slight haze but remains mostly at higher altitudes unless it is captured by rain droplets. The layer of dust on cars is a clear sign of this.

More important in the current situation is the weather pattern, which is relatively stagnant and which puts a cap on the lowest layer of the atmosphere, trapping emissions of small particles as well as other reactive gases. The MACC-II European air quality forecasts clearly show this effect for the UK/Netherlands region. Both PM10 (small particles) and PM2.5 (very small particles) are enhanced over a large area. In the Netherlands this has resulted in moderate smog as published by the Dutch National Institute for Public Health and the Environment (RIVM). In the UK PM10 and PM2.5 have reached even higher values through the combination with strong local emissions in the London area. It shows all too well that forecasting air quality is complex and long-range transport, weather, regional and local emissions all play a role.

OVM_ENSEMBLEMEDIAN_pm2p5_2014040200_006_small.pngThe image on the left shows the MACC-II forecast of PM2.5 for Wednesday 2 April for Europe based on its ensemble of regional air quality models. On top of the forecast are coloured dots representing actual observations (click on image for larger version). It is clear that the MACC-II forecast captures the large scale pollution pattern very well, but underestimates some of the local effects, most notably in the large English cities (London, Birmingham and Manchester). The daily forecast from the MACC-II ensemble can be found on the forecast web pages.

Finally the animation below illustrates the flow of desert dust from the Sahara, which has left its trace on cars as well as contributing to the amount aerosol particles in the atmosphere. Especially in spring, when weather patterns change from winter to summer regimes, Saharan dust can be transported far North by the prevailing winds.

MACC-II supports both the UK and Dutch air quality forecasting communities by providing boundary conditions for the relevant domains.