PM2.5 sampling. The PM2.5 sample collection was performed simultaneously at Centro (8 m above ground level) and Miravalle (10 m above ground level) sites, by means of a Partisol 2300 model (Rupprecht and Patashnick Co.) sampler, for 24 h (00:00 to 24:00 h) at a rate of 16.7 L min–1 every six days between January and August 2008.