A Method to Identify Traffic-Related Particulate Matters in Urban Air

Abstract:

With economic prosperity and urbanisation, traffic-related air pollution is becoming a major concern to many developing Asian cities. Before any effective measures to address PM pollution problems in urban air could be effectively adopted, the sources of PM as well as their contribution to the ambient air concentrations should be known. In this work, a method was developed to identify traffic-related PM in urban air. At a heavily trafficked site in Stuttgart Neckartor (Germany), the daily limit value of 50 µg/m³ for PM10 prescribed by the European legislation was exceeded more than 170 times per year. In 2006, the PM10 annual average value was 55 µg/m³ which exceeded the EU limit value of 40 µg/m³ by approximately 38 %. PM samplings were conducted by means of cascade impactors during the PM10 pollution episodes from 12 January to 26 March 2006 at the traffic site of Neckartor and an urban background site in Schlosspark. The sites were characterised by different exposure to traffic emissions, enabling the assessment and comparison of PM concentration levels and particle size distributions between the traffic and urban background sites. After sampling, the size, morphology, elemental composition and mineralogy of PM from the respective impactor stages were individually analysed with Scanning Electron Microscopy (SEM) with an integrated Energy Dispersive X-ray analysis (EDX) system. Three main potential PM sources were identified from an average of ten samples with PM10 concentrations greater than 80 µg/m³: 44 % of the PM10 as resuspended road dust (2.1-10.0 µm), 38 % of the PM10 as urban background dust load (0.7-2.1 µm), and 18 % of the PM10 as diesel soot particles (<0.7 µm). Considering PM abatement strategies, the dominance of resuspended road dust shows that the reduction of this PM fraction is an important goal for successful reduction measures for urban PM10. Although the studied site was in the city of Stuttgart, the successful implementation of the method could be adopted in Asian cities as well.

Keywords: urban air quality, particulate matters, cascade impactors, SEM/EDX