Multi-year chemical composition of the fine-aerosol fraction in Athens, Greece, with emphasis on the contribution of residential heating in wintertime

Abstract

Abstract. In an attempt to take effective action towards mitigating pollution episodes in Athens, precise knowledge of PM2.5 composition and its sources is a prerequisite. Thus, a 2-year chemical composition dataset from aerosol samples collected in an urban background site in central Athens from December 2013 to March 2016 has been obtained and a positive matrix factorization (PMF) was applied in order to identify and apportion fine aerosols to their sources. A total of 850 aerosol samples were collected on a 12 to 24 h basis and analyzed for major ions, trace elements, and organic and elemental carbon, allowing us to further assess the impact of residential heating as a source of air pollution over Athens. The ionic and carbonaceous components were found to constitute the major fraction of the PM2.5 aerosol mass. The annual contribution of the ion mass (IM), particulate organic mass (POM), dust, elemental carbon (EC), and sea salt (SS) was calculated at 31 %, 38 %, 18 %, 8 %, and 3 %, respectively, and exhibited considerable seasonal variation. In winter, the share of IM was estimated down to 23 %, with POM + EC being the dominant component accounting for 52 % of the PM2.5 mass, while in summer, IM (42 %) and carbonaceous aerosols (41 %) contributed almost equally. Results from samples collected on a 12 h basis (day and night) during the three intensive winter campaigns indicated the impact of heating on the levels of a series of compounds. Indeed, PM2.5, EC, POM, NO3-, C2O42-, non sea salt (nss) K+ and selected trace metals including Cd and Pb were increased by up to a factor of 4 in the night compared to the day, highlighting the importance of heating on air quality in Athens. Furthermore, in order to better characterize wintertime aerosol sources and quantify the impact of biomass burning on PM2.5 levels, source apportionment was performed. The data can be interpreted on the basis of six sources, namely biomass burning (31 %), vehicular emissions (19 %), heavy oil combustion (7 %), regional secondary (21 %), marine aerosols (9 %), and dust particles (8 %). Regarding night-to-day patterns their contributions shifted from 19 %, 19 %, 8 %, 31 %, 12 %, and 10 % of the PM2.5 mass during day to 39 %, 19 %, 6 %, 14 %, 7 %, and 7 % during the night, underlining the significance of biomass burning as the main contributor to fine particle levels during nighttime in winter.

Carbonaceous Aerosols in Contrasting Atmospheric Environments in Greek Cities: Evaluation of the EC-tracer Methods for Secondary Organic Carbon Estimation

“…The large R 2 values (0.72-0.92) in Ioannina and Athens largely indicate the impact of local primary sources (mainly traffic and biomass burning). A strong linear association (R 2 = 0.88; slope = 2.36) has been reported at the same site in Athens during the three winter periods (2013/2014, 2014/2015, 2015/2016), revealing the continuous, long-term effect of primary RWB emissions in the area [24]. In contrast, the much lower OC/EC correlation in Heraklion (R 2 = 0.45) possibly suggests increased SOC formation (photochemical formation is possible even during winter in Southern Greece due to fair weather conditions) and the influence from regional background carbonaceous aerosols.…”

“…The EC mean concentration in Ioannina (4.14 ± 3.67 µg m −3 ; range of 0.14-24.42 µg m −3 ) was found to be about double that of those in Athens (2.44 ± 3.28 µg m −3 ) and Heraklion (2.29 ± 2.40 µg m −3 ) ( Table 1), and much higher than previously reported values in Athens, for instance, 2.8 ± 1.2 µg m −3 during the winters of 2013-2015 [24]. Other studies have measured average winter BC concentrations in Athens in the range of 2.4-3.0 µg m −3 [25,30,32,34], much lower than the EC levels in Ioannina, whereas the pre-recession EC levels in Greek cities were even lower [20,28,36,56].…”

“…The bulk air-sample (TSP) measurements in Heraklion were also performed separately for daytime and night-time during January to February 2013, using the same sampling device as in Ioannina (Table S1). In Athens, PM 2.5 sample measurements were performed at the atmospheric monitoring station in Thissio (Figure 1), an urban-background site located in the city center [24,46]. Particles were collected using a Dichotomous Partisol Sampler 2025 (Thermo Scientific Inc.), at a flow rate of 16.7 l min −1 , also at 12 h (day/night) intervals (Table S1).…”

“…The interference from other coarse OC particles (e.g., bio-aerosols) is expected to be low [36]. The detection limits for OC and EC were 0.26 and 0.05 µg C cm −2 , respectively, and the final concentrations were blank corrected [24]. In addition, water-soluble species (Cl − , SO 4 2− , NO 3 − , C 2 O 4 2− , NH 4 + , K + , Na + , Mg 2+ , Ca 2+ ) at all stations were detected from filters using ion chromatography [20].…”

“…Biomass burning (BB) is a major source of carbonaceous aerosols in the atmosphere [1,15,16] and contributes to the production of secondary organic aerosol (SOA) [17,18]. Since the winter of 2012-2013, the atmospheric composition in Athens and other major Greek cities has been substantially modified due to enhanced emissions from residential wood burning (RWB), as a consequence of the economic recession and the increase in the price of heating oil [19][20][21][22][23][24]. The result was a remarkable escalation in winter night-time concentrations of particulate matter (PM), carbonaceous aerosols, and biomass-burning tracers, documented mainly in Athens [25,26], but also in other Greek cities such as Thessaloniki [19] and Patras [27].…”