Urban Centers With Most Polluted Air: North East Of Barcelona And South East Of Madrid

To determine the most polluted areas of north east and central Spain in the summer, a team of researchers from the Universidad Politécnica de Cataluña (Polytechnic University of Catalonia) (UPC) and the Barcelona Supercomputing Centre (BSC) has quantified with great precision the atmospheric processes that contribute to the concentration of pollutants.

"The worst air quality levels are observed in areas leeward of Barcelona and Madrid, due to the plume of urban contamination that affects the south-south-east region of Madrid and north-north-east of Barcelona", María Gonçalves, principal author of the study and researcher at BSC, explains to SINC.

The work, led by José María Baldasano and Pedro Jiménez of BSC and recently published in Atmospheric Chemistry and Physics, has been centred around Catalonia and the Autonomous Community of Madrid as they are home to the two most populated cities, Barcelona and Madrid, "where episodes of atmospheric contamination are frequent", the scientist adds.

On 17th and 18th June 2004, the researchers selected one of the most acute episodes of photochemical contamination in these areas; a meteorological phenomenon "which occurs in 78% of cases in the summer", the researcher emphasizes.

Atmospheric contamination mainly comes from emissions derived from urban activities, particularly traffic, "although industrial emission points or activities carried out at the port, especially in Barcelona, cannot be discounted", Gonçalves stresses.

How are pollutants dispersed?

In the centre and north east of Spain there are different methods for the dispersion of pollutants. In the coastal area of Barcelona, the nature of the breezes and the complex topography create layers of elevated contamination, which, during the night, "can act as a reserve of pollutants over the Mediterranean area", the chemical engineer points out.

In the case of Madrid, which is more continental, transport is dominated by "the formation of a convection cell" -a bubble created by the rise and fall of air due to temperature differences- caused by surface heating". The nitrogen oxides emitted in urban areas and by the road network "are transported leeward where they undergo a chemical reaction or are deposited at surface level", states Gonçalves.

During the days observed, the two cities exhibited high concentration levels of dust particles (PM10) and nitrogen dioxide (NO₂) above the urban area. "During the selected episode, higher concentrations of ozone (O3) were observed over Madrid and higher levels of NO₂ and PM10 in Barcelona", the researcher reports.