Particulate matter and black smoke concentration levels in central Athens, Greece

This study presents the statistical analysis of PM10 and PM2.5 concentrations (measured at a central site, in the Athens area), along with black smoke (BS) data, for a 2-year period. The biennial average concentrations of PM10 and PM2.5 were 75 and 40 μg m−3. The respective average concentration of BS, as estimated by the OECD method, was 108 μg m−3. Severe exceedances of the PM10 air quality standards were recorded. The seasonal variation of PM10 and BS was less pronounced than the variation of PM2.5, which concentration was elevated by 14.2% during the cold period. Concentrations of all three pollutants were significantly lower during weekends; however, PM2.5 and BS displayed a more uniform weekly distribution pattern. PM10 particles were found to be almost equally comprised by PM2.5 and PM10-2.5 particles (PM2.5/PM10 ratio=0.53±0.09 μg/m3). The average PM10/BS value was found lower than unity revealing the inappropriateness of the used reflectance conversion method, for the estimation of mass-equivalent BS concentrations, in the study area, where diesel-powered vehicles mainly control emissions of light-absorbing substances. Important reductions in concentrations were observed during days when drivers of diesel-powered taxies and transportation buses went on strike (reaching 40% for BS). Calm wind conditions were found to have an incremental effect on particle concentrations and were also associated with the appearance of persistent episodic events. Increased PM levels were also observed during southern-southwestern wind flows while significantly lower-than-average concentrations were measured during precipitation events. Separate regression analyses were performed for PM10, PM2.5 with BS and NOx as independent variables, in an attempt to estimate the relative contribution of specific source types (diesel-powered vehicles) to measured particle levels. The contribution of the diesel-exhaust component to PM10 mass was estimated at 49.9%, while the corresponding contributions to PM2.5 mass concentrations was 53.8%. These results may have important implications with the oncoming decision of national authorities to allow the purchase of diesel-powered private cars to the residents of the Greater Athens Area, which was forbidden up to this day.