Analysis of PM10 and PM2.5 Concentrations in an Urban Atmosphere in Northern Spain

This work analyses levels of particles PM10 and PM2.5 recorded at four air-quality monitoring stations located in the urban area of Valladolid (Spain) during 2015-2016. To achieve this, the evolution of particle concentrations at different time scales was determined. Average concentrations ranged from 15.3 to 17.6 µg m^-3 for PM10 and between 8.9 and 14.8 µg m^-3 for PM2.5. The highest monthly means were recorded in autumn and winter. The difference between mean concentrations at weekends and on weekdays for PM10 was around 3 µg m^-3 at most of the measuring stations and was 1 µg m^-3 for PM2.5. Two concentration peaks were found during the day, one in the morning and the other in the evening, which evidenced the influence of traffic and other anthropogenic activities on PM concentrations. Their mean values were approximately 21 and 17-21 µg m^-3, respectively, for PM10. Mean maximum values for PM2.5 were 12 µg m^-3, except at one of the measuring sites, with 17 µg m^-3 for the morning maximum and 1 µg m^-3 more for the nocturnal peak. In addition, the impact of long-distance transport of air masses in the study area was analysed by applying a HYSPLIT trajectory model, taking into account backward trajectories of European, African, and Atlantic origins as well as local conditions. In particular, high concentration events due to Saharan dust intrusions are presented. Finally, background levels of particle concentrations estimated at most sampling areas were around 15 and 7.7 µg m^-3 for the PM10 and PM2.5 particle fractions, respectively.