PM2.5 source apportionment and transport cluster analysis

Abstract

Introduction Source apportionment studies of particulate matter are common and have either been performed as source region analyses or by source type. The first type use air mass back trajectories and the latter one uses source apportionment techniques such as principal component analysis, chemical mass balance or positive matrix factorisation (PMF). However, by combining the two approaches it is possible to estimate the relative importance of emitters in different regions. Methods In this study we have collected one year of daily PM2.5 samples and made elemental analysis of the samples using EDXRF. Source apportionment was carried out using PMF with the US EPA PMF5.0 software. The sources long-range transport (LRT), LRT-Pb (lead containing LRT), ship emissions, combustion, marine, and resuspension were identified. We also calculated air mass trajectories using the HYSPLIT (version 4.9) model. Six transport clusters were identified, South Scandinavia (S-Scandic), North Scandinavia (N-Scandic), Baltic Sea (BalticS), Eastern Europe (E-Eur), UK/North Sea/Denmark (UK-NorthS-DK) and North Atlantic Ocean (N-Atlantic. The frequency of occurrence was 28, 21, 107, 38, 76, and 91 days, respectively. Results From the PMF analysis we found that LRT is the dominating contributor to PM2.5 levels and across all six transport clusters. LRT contributes 48% of the PM2.5 levels followed by ship emissions (20%) and combustion (19%). The transport cluster associated with the highest PM2.5 levels was E-Eur followed by S-Scandic, UK-NorthS-DK, and BalticS. After considering the frequency of the transport clusters during the study period, the transport clusters associated with the highest PM2.5 levels were UK-NorthS-DK, S-Scandic and N-Atlantic, while E-Eur only contributed 9% towards PM2.5 levels. Conclusion Our study adds knowledge to one of six research directions identified in a review, namely the combination of back-trajectory modelling with source apportionment analyses.