Cross-validation of methods for quantifying the contribution of local (urban) and regional sources to PM2.5 pollution: Application in the Eastern Mediterranean (Cyprus)
Elie Bimenyimana, Jean Sciare, Konstantina Oikonomou, Minas Iakovides, Michael Pikridas, Emily Vasiliadou, Chrysanthos Savvides, Nikos Mihalopoulos
Abstract
A comprehensive (1-year-long) daily-resolved filter-based PM 2.5 chemical speciation database was built over Cyprus (Eastern Mediterranean), encompassing various sites with different typologies (urban traffic, urban background and regional background). Such experimental strategy was designed and implemented with the view to quantify the contribution of local (Cypriot cities) versus regional (Eastern Mediterranean & Middle East) pollution sources on fine PM levels in Cyprus using the “Lenschow” approach (Lenschow et al., 2001). On an annual basis, fine PM fraction originated mainly from regional sources (53–61 %), while during winter a totally different pattern was observed, with local PM sources being the dominant ones (up to 70 %) due to enhanced biomass burning for domestic heating and unfavorable meteorological conditions enhancing stagnation and accumulation of air pollution close to the ground. At that period, the urban PM 2.5 was found to be predominantly made of carbonaceous species (> 70 %). Dust from local sources unexpectedly dominated the summertime local PM 2.5 (37–47 %). The results derived from “Lenschow” approach were quantitatively compared against an independent PM source apportionment approach using Positive Matrix Factorization (US EPA PMF 5.0) to assess more-local versus more-regional PM sources. We show here that both approaches applied over Cyprus have led to consistently similar results, further cross-validating the robustness of the two techniques. The influence of regional hotspots was further confirmed by using the Potential Source Contribution Function (PSCF) model which pinpointed the Middle East as the main source region of fine PM pollution affecting Cyprus. • Major impact (58% on average) of regional sources on PM 2.5 levels in Cypriot cities • Middle East identified as the main fine PM pollution hotspot affecting Cyprus • Locally emitted combustion-related carbonaceous aerosols dominate (>70 %) the fine PM in Cypriot cities during winter • Re-suspended dust is the main constituent (37–47 %) of the summertime local fine PM in Cyprus • Strong agreement between Lenschow and PMF approaches to quantify the respective contribution of local (urban) versus regional sources to PM 2.5 pollution