Source apportionment of highly time resolved trace elements during a firework episode from a rural freeway site in Switzerland

This is the authors' abstract. We don't add key points for this paper.

Trace element measurements in PM10 were performed with 1 h time resolution at a rural freeway site during summer 2015 in Switzerland using the Xact multi-metals monitor. On average the Xact 625 elements (without accounting for oxygen and other associated elements) make up about 20 % of the total PM10 mass (14.6 µg m−3). Subsequently, a source apportionment by positive matrix factorization (PMF) implemented via the Source Finder software (SoFi Pro) was applied. Eight different sources were identified (notable elements in brackets) for PM10: fireworks-I (K, S, Ba, Cl), fireworks-II (K), sea salt (Cl), secondary sulfate (S), background dust (Si, Ti), road dust (Ca), traffic-related (Fe) and industrial (Zn, Pb). The major components were secondary sulfate and traffic-related followed by background dust and road dust factors, explaining 21 %, 20 %, 18 % and 16 % of the analysed PM10 elemental mass, respectively, with the factor mass not corrected for oxygen content. Further, there are minor contributions (on the order of a few percent) of sea salt and industrial sources. The regionally influenced secondary sulfate factor experiences negligible resuspension, and concentrations are similar throughout the day. The significant loads of the traffic-related and road dust factors with strong diurnal variations highlight the continuing importance of vehicle-related air pollutants at this site. Enhanced control of PMF using SoFi Pro allowed for a successful apportionment of transient sources such as the two firework factors and sea salt, which remained mixed when analysed by unconstrained PMF.