Analysis of a severe pollution episode in Valencia (Spain) and its effect on ground level particulate matter

This study analyzes the atmospheric particles concentration at ground level during a severe pollution event that took place in Valencia (Spain) from 7 to 12 February 2011. The episode was related to a subtropical anticyclone system that affected the Iberian Peninsula and western Europe. The dominant anticyclone imposed an extended low gradient pressure system and a low mixing layer height in the region that caused the accumulation of pollutants over the western Mediterranean. Moreover, the stagnant conditions led to the formation of the local sea breeze, accompanied by an increase of relative humidity and the decrease of ambient temperature. Our study is mainly focused on the analysis of particulate matter levels (PM10 and PM2.5) and the concentration of black carbon (BC) measured at the Burjassot station, Valencia (Spain). BC and PM levels were found to steadily increase during the event (from 3.2μg/m3 and 33μg/m3 before the event to 4.9μg/m3 and 61μg/m3 for BC and PM2.5, respectively) and abruptly decreased to 1.3μg/m3 and 14μg/m3, respectively, after a cold front swept the Iberian Peninsula, bringing fresh air from the Atlantic and increasing the mixing layer height, thus ventilating and diluting the accumulated pollutants. As a consequence, the EU limit of 50μg/m3 for PM10 size fraction was exceeded during days 7 to 12 February 2011 at Valencia, Spain.