Source apportionment analysis at an urban background site, a roadside site, and the resulting roadside increment in London, UK

<p>Traffic remains a key source of PM_2.5 and PM₁₀ in urban environments and contributes to PM in the form of exhaust related particles and non-exhaust related particles (Grigoratos and Martini, 2014). It is expected that due to traffic fleet changes and stricter exhaust emissions controls the relative contribution of non-exhaust traffic related particles, such as brake and tyre wear, but also of other urban sources, such as wood smoke and cooking aerosols, will become more significant. To understand these changes in relative contribution, sources need to be identified and quantified in different urban environments. High time resolution measurements of PM composition, such as those from the Xact instrument allow for a more accurate identification and quantification of sources as the high time resolution reflects short term changes due to emission and atmospheric processing. Here we present a comparison of positive matrix factorisation (PMF) analysis at an urban background site, a roadside site, and of the resulting roadside increment. This work aims to improve the identification of non-exhaust traffic emissions.</p> <p>Hourly PM₁₀ measurements of a range of elements were made with the Xact at an urban background and a roadside location in London between Aug. 2019 and Aug. 2020. Source contributions were determined with PMF using the Source Finder software (SoFi) (Canonaco et al., 2013). PMF is carried out in steps: i) initial factor profiles are established for the roadside and background location; ii) factor profiles of the roadside increment are established; iii) the roadside increment profiles are used to improve the factor identification at the roadside and background and results evaluated in comparison with the initial profiles. Black carbon, PM₁₀, PM_2.5 mass concentrations and NO_x were used to verify PMF results.</p> <p>PMF analysis was initially performed on roadside increment data. The profiles identified were then used to improve the combined PMF for both sites. In this novel approach, the advantages of utilizing the roadside increment are explored to investigate the identification of factors which can be used to quantify traffic impact more accurately at roadside and background locations.</p> <p>This work was supported by the Natural Environment Research Council (NERC) under grant NE/T001909/2.</p> <p>References</p> <p>Canonaco et al, (2013). AMT 6, 3649-2013</p> <ul> <li>Grigoratos and G. Martini, 2014; Non-exhaust traffic-related emissions - Brake and tyre wear PM. Report no. Report EUR 26648 EN</li> </ul>