Source apportionment of indoor PM2.5 at a residential urban background site in Malta

Abstract

In this study we carry out receptor modelling via Positive Matrix Factorisation (PMF) to identify and quantify the main natural and anthropogenic sources of indoor PM2.5 at an urban background site in the island of Malta. Quartz and PTFE filters were collected, analysed gravimetrically and chemically, using ICP-MS, IC and an OC-EC aerosol analyser to determine the concentrations of PM2.5, 18 elements, 5 ions, organic carbon (OC) and elemental carbon (EC). The EPA PMF was used to identify 8 factors that were affecting the receptor site. Seven outdoor sources were identified: ammonium sulfate (31%), traffic (10%), shipping (10%), sea salt (9%), fireworks (4%), Saharan dust (2%) and industrial (2%). An indoor factor was also identified, which contributed 26% to the indoor PM2.5. Cooking and e-cigarette smoking were identified as the main contributors to the indoor factor. The mean indoor PM2.5 concentration (5.7 μg m−3) at the receptor site was slightly higher than the WHO AQG limit of 5 μg m−3. Uniquely for Malta, we have isolated a fireworks factor for indoor PM2.5. Fireworks have been identified as being responsible for most of the Sb and Ba and hence are of great concern due to the health implications of these toxic elements.