SECONDARY INORGANIC VERSUS CARBONACEOUS FRACTION AND MASS CLOSURE OF PM2.5 IN URBAN ENVIRONMENT (ATHENS, GREECE)

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1 Proceedings of the 13 th International Conference on Environmental Science and Technology Athens, Greece, 5-7 September 213 SECONDARY INORGANIC VERSUS CARBONACEOUS FRACTION AND MASS CLOSURE OF PM2.5 IN URBAN ENVIRONMENT (ATHENS, GREECE) E. REMOUNDAKI 1, E. MANTAS 1, C. THEODOSI 2, P. KASSOMENOS 3 and N. MIHALOPOULOS 2 1 Laboratory of Environmental Science and Engineering, School of Mining and Metallurgical Engineering, National Technical University of Athens, Heroon Polytechniou 9, 1578 Zografou, Greece. 2 Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, PO Box 228, 713 Heraklion, University of Crete, Greece. 3 Laboratory of Meteorology, Department of Physics, University of Ioannina, University Campus GR-4511, Ioannina, Greece. remound@metal.ntua.gr EXTENDED ABSTRACT To identify the contribution of secondary inorganic and carbonaceous components in PM 2.5, 24-h mass and chemical composition measurements were carried out in the frame of a systematic monitoring at an urban site, at the National Technical University of Athens campus. In this paper the results concerning the period from February 211 to September 212 are presented. Mean and median daily concentrations of PM 2.5 for the studied period were 17 and 15 μg/m 3 respectively, showing a decreasing tendency compared to previous years data. PM 2.5 concentrations did not presented significant seasonal variation. Secondary inorganic ions (SIA=sum of sulfates, nitrates and ammonium) and carbonaceous material (organic carbon (OC) and elemental carbon (EC)) were the most abundant constituents of PM 2.5. SIA represents 89% of the total mass of inorganic ions determined. Ionic balance calculations revealed a well balanced inorganic ionic content with a slight cation deficit. Sulfates concentrations increased during the summer months while nitrates presented the opposite pattern. EC concentrations were higher during the cold season than those observed for the warm season. Although the upward trend of OC concentrations during the months of April-July, pointing out that photochemically produced secondary OC becomes significant, organic carbon concentrations did not present a significant seasonal pattern and this is mainly due to the reduction of the primarily emitted OC during the summer months. The ratio OC/EC presented a significant seasonal pattern with higher values during the warm season. For the mass closure calculations, six components were considered: SIA, Organic Matter (OM), Elemental Carbon (EC), Dust, Mineral anthropogenic component (MIN) and Sea Salt (SS). SIA, OM and EC contribute in PM 2.5 mass about 33%(±9), 32%(±9) and 5%(±3) respectively representing a fraction greater than 7% of PM 2.5 mass. Dust contribution became significant in cases of Saharan dust transport events (12-5%) and was calculated to be about 3-5% in absence of dust events. The anthropogenic mineral fraction contribution was calculated to be about 3%. Finally, a mean value of 4% for sea salt contribution in PM 2.5 was calculated from the whole data set. Keywords: Secondary Inorganic Aerosol, Organic Matter, Elemental Carbon, mass closure. 1. INTRODUCTION Enhanced concentrations of locally emitted and long range transported particulate matter, absence of precipitation from spring to late autumn, favorable conditions for the formation of photochemical smog and unfavorable topography for dispersion of air pollutants

2 characterize the Greater Athens Area (GAA), a region of 45 km 2 where half of the population of the country is accumulated (> 4 million). Vehicular traffic is the main cause of air pollution-related problems. Emissions from the use of fuel oil in central heating and those from the industrial activity in the Thriassion plain, located to the west of the GAA, constitute the main local contributors in the atmospheric particulate charge. Although the chemical composition and mass closure of PM 1 is enough documented for Greek urban environments (Gerasopoulos et al., 26; Grivas et al., 28; Terzi et al., 21; Theodosi et al., 211), results on PM 2.5 composition are few and recent covering relatively short sampling campaigns (Karageorgos et al., 27; Sillanpaa et al., 26; Theodosi et al., 211). Simultaneous quantitative estimation of secondary inorganic and carbonaceous components in PM 2.5 for long time series and the corresponding mass closure are not reported in literature in our knowledge for the Greater Athens Area. The present paper reports results on the mean daily concentrations and composition of PM 2.5, focusing on secondary inorganic and carbonaceous components, from 24-hour PM 2.5 samples at an urban site in Athens. The composition of PM 2.5 is discussed in terms of, ionic, EC/OC and elemental concentrations levels, their relative contribution in PM 2.5 and their correlations. The temporal and seasonal variability of the determined species are also presented and discussed. The ionic balance is presented and the neutralization capacity of the atmospheric acidity is discussed. Finally, mass closure is attempted considering the following components: Secondary Inorganic Aerosol (SIA), Organic Matter (OM), Elemental Carbon (EC), Dust, Mineral anthropogenic component (MIN) and Sea Salt (SS). 2. MATERIALS AND METHODS The methodology followed is already presented in detail in previous papers (Remoundaki et al., 211; Remoundaki et al., 213a; Remoundaki et al., 213b) and is briefly described following. Twenty four hours aerosol samples were collected at the top of the building of the School of Mining and Metallurgical Engineering at the National Technical University of Athens campus at 14 m above ground level. The sampling point is fully exposed to wind and free all around of other obstacles (Remoundaki et al., 211). PM 2.5 sampling was carried out using a TCR TECORA (Sentinel PM) operating at l/min, constructed and calibrated in order to comply with European Standard EN1497 for standard sampling of PM 2.5. Aerosol samples were collected on PTFE membranes (PM 2.5 air monitoring membranes Whatman). The results of 148 samples are reported in the present paper corresponding to the period form February 211 to March 212. For organic carbon (OC) and elemental carbon (EC) determinations high purity quartz filters were used prefired at 45 for 12 h. Sampling on quartz filters was carried out with a time span of 1 sample/week. Seventy five samples have been collected between February 211 and September 212. In order to determine PM 2.5 concentrations, the membranes were weighted before and after sampling according to the procedure described in EN12341 (Annex C) using a Mettler Toledo MS15 with a resolution of 1 μg in the air conditioned weighing room of the laboratory. The pre weighted membranes were charged to the filter supports and sampler cassette under the laminar flow hood. Filter blanks and blank field samples were also prepared and analyzed together with samples. The elemental determinations for Al, Si, Fe, Ca, K, Ti and S have been carried out by WDXRF (Thermo ARL Advant XP, sequential XRF) with Rh X-ray tube at 3 kv, 3 ma. The concentrations of Cl -, NO 3-, SO 4 2-, Na +, K +, NH 4+, Ca 2+, Mg 2+ were determined by a Metrohm 732 IC Separation Center connected to a 732 IC conductivity detector and 753 Suppressor Module for anions determination. A Metrosep Anion Dual 2 column was used for anions determinations (eluent: 2 mmol/l NaHCO mmol/l Na 2CO 3 with chemical suppression, flow:.8 ml/min) and a Metrosep C415/4. was used for cations determinations (eluent: 1.7 mmol/l HNO 3,.7 mmol/l dipicolinic acid, Flow:.9 ml/min). Trace metals: Zn, Pb, Cu, Ni, Cr have been determined by GFAAS. Organic carbon (OC)

3 and elemental carbon (EC) analysis concentrations were determined on quartz filters by Thermal Optical Transmission method in a Sunset Laboratory OC/EC Analyser using EUSAR2 protocol (Koulouri et al., 28; Terzi et al., 21). Following OC/EC analysis, the remaining part of the quartz filters was extracted with 1 ml of ultrapure water for ion chromatography analysis. 3. RESULTS AND DISCUSSION 3.1. Summary of PM 2.5 mass and species concentrations The mass concentration of PM 2.5 and the concentrations of all the species determined are shown on Figure 1 which is a graphical representation of key values from summary statistics. PM 2.5 arithmetic mean and median concentrations were calculated to be 17 μg/m 3 and 15 μg/m 3 respectively while only 15% of the values determined exceeded the target value of 25 μg/m 3. These values are lower to those presented in a previous paper for the same sampling site and for the year 21 where PM 2.5 mean and median concentrations were calculated to be 2 μg/m 3 and 19 μg/m 3 respectively (Remoundaki et al., 213a; Remoundaki et al., 213b). Another difference between year 21 and the period of the present study, is that, during 21, the exceedances of the target value were more frequent, corresponded to 22% of the values measured and the highest values corresponded to Saharan dust transport episodes. Mean concentration for dust events was equal to 29 μg/m 3 while in absence of dust event was equal to 17 μg/m 3 (Remoundaki et al., 213a; Remoundaki et al., 213b) identical to that reported in this study. Moreover, the reduction of the vehicular traffic due to the economic crisis may also be a reason of the observed trend. Three distinct groups of species can be seen from figure 1: 1. The most abundant species in PM 2.5: Sulfates (sulfur), nitrates, ammonium, organic and elemental carbon. These species of anthropogenic origin present concentration levels of 1 ng/m 3 and above. 2. The elements which are characteristic of natural sources: crustal origin elements (Al, Si) and elements of mixed origin with a significant crustal component such as Fe, Ca, K as well as Na representing the tracer of the marine source, belong to the second group. The concentrations of these elements are at the level of 1 ng/m Trace elements and heavy metals belong to the third group with concentrations at the level of 1-1 ng/m Species of anthropogenic origin: Secondary inorganic ions, organic and elemental carbon. Table 1 (a) presents the mean values and the range of the concentrations of the ionic species and organic and elemental carbon. On the same table, 1(b) are shown the correlation coefficients between the species. Sulfates and organic carbon are by far the most abundant species among those reported on table 1 and their mean concentrations are quite similar. The mean concentrations of the species are in good agreement with respective values reported for the same site (Remoundaki et al., 213a) and in literature for both ionic (Karageorgos et al., 27; Theodosi et al., 211) and carbonaceous components (Grivas et al., 212). Especially for the carbonaceous component, the most recent average values for OC: 6.8 μg/m 3 and EC:2.2 μg/m 3 have been reported for central Athens and for PM 1 by Grivas et al. (Grivas et al., 212). Our results on OC and EC concentrations in PM 2.5 can be considered reasonable if we also take into account a mean PM 2.5/PM 1 ratio of about.5 reported for Athens in previous studies (Theodosi et al., 211).

4 Figure 1. PM 2.5 and determined species concentrations. Multiplication sign: percentiles (1 99 %), small open square: mean, box: % percentile, dash: median The sum of the mean concentrations of Secondary Inorganic Aerosol (SIA) (sum of sulfates, nitrates and ammonium) and of the carbonaceous fraction (OC and EC) (Table 1(a)) is equal to 11.3 μg/m 3 representing 66% of the mean mass of PM 2.5 (17μg/m 3 ). Moreover, SIA represents 36% and the sum of OC and EC represents 3% of the mean mass of PM 2.5 respectively. If now we transform organic carbon (OC) to organic matter (OM), by multiplying the concentration of OC by 1.6 (Grivas et al., 212; Remoundaki et al., 213a; Terzi et al., 21), the sum of SIA and the carbonaceous component (OM+EC) is equal to 13.8 μg/m 3 representing 81% of the mean mass of PM 2.5 (17 μg/m 3 ). The carbonaceous fraction (OM+EC) represents 45% of the mean mass of PM 2.5. These results are in good agreement with those reported in literature for the contribution of SIA and the carbonaceous component in the total mass of PM 2.5 for Athens (Grivas et al., 212; Karageorgos et al., 27; Sillanpaa et al., 26; Theodosi et al., 211). From table 1(b), it is important to point out that the highest correlation observed is between sulfates and ammonium which seems to be the main neutralizing agent of sulfates. Important correlations are also observed between OC and ionic components except Na, Mg and Cl. EC, nitrates and potassium are highly correlated due to their emissions mainly by vehicular traffic. Fig. 2(a) presents the mean relative contribution of the main inorganic ionic species for the period of sampling. Sulfates, ammonium and nitrates represent 89% of the total mass of inorganic ions determined. Sulfates percentage is at the same level to that reported for the fine fraction and taking also into consideration the sulfates levels reported for urban and background sites in the region, it is apparent that sulfates levels above Greece are also largely controlled by long-range transport and processes evolving at a large spatial scale (Koulouri et al., 28; Theodosi et al., 211). The results from the calculation of the ionic balance are shown on Fig. 2(b). The slope of the regression line is equal to 1.8 meaning a well balanced aerosol with a slight cation deficit.

5 (a) Ion Concentration (ng/m 3 ) n=148 Mean Range 2- SO (S) (1671) (191-49) + NH NO Ca Na K Mg Cl OC/EC Concentration (ng/m 3 ) n=75 Mean Range OC EC (b) OC EC Cl NO 3 SO 4 Na NH 4 K Ca Mg OC 1 EC,74 1 Cl,32,67 1 NO 3,62,7,57 1 SO 4,64,26 -,3,39 1 Na -,12 -,1,31,9 -,5 1 NH 4,78,46,15,57,91 -,18 1 K,81,7,29,59,53 -,1,68 1 Ca,32,11 -,5,22,26,3,18,29 1 Mg -,4 -,8 -,6 -,1,5 -,2,8 -,17,5 1 Table 1. (a) Mean and range of concentrations of ionic species, organic and elemental carbon, (b) Correlation coefficients among the species. Figure 2. (a) Mean relative contribution of the main inorganic ionic species (b) Ionic balance (equivalents) From figure 3, a seasonal trend is observed for nitrates with higher values during winter and lower values during summer mainly for the first year. This trend, already observed in previous studies (Remoundaki et al., 213a; Theodosi et al., 211), is due to the instable ammonium nitrate formation during winter, while ammonium nitrate formation does not occur during summer because of the higher temperature of the air. The higher values of sulfates concentrations for the summer are associated to enhanced photochemistry, lack of precipitation, low air masses renovation at regional scale or the increment of the summer mixing layer depth favoring the regional mixing of polluted air masses. Moreover, during summer, long range transported sulfur from northern regions is added on top of the locally emitted (Mihalopoulos et al., 27; Terzi et al., 21; Theodosi et al., 211). Ammonium concentrations do not present a significant seasonal trend. EC concentrations show a net seasonal trend with higher values during the cold season and lower values during the warm season due to the reduction of vehicular traffic. Although the clear upward trend of OC concentrations during the months April-July, the seasonal trend is not clear because during the cold season, vehicular traffic contributes significantly in primarily emitted OC while the emissions of this source are much lower during the summer months. The reduction of emissions of OC is balanced by an amount of secondary produced OC by photochemistry during the warm season. The ratio OC/EC presents, as

6 expected, a net seasonal pattern with higher values during the warm season and lower values during the cold season Mass closure For the purpose of chemical mass closure, the following components have been considered: Secondary Inorganic Aerosol (SIA), Organic Matter (OM), Elemental Carbon (EC), Dust, Mineral anthropogenic (MIN) and Sea Salt (SS). The way each component was calculated is presented in detail in Remoundaki et al. (Remoundaki et al., 213a). Briefly, Secondary Inorganic Aerosol (SIA) is represented by the sum of nss-so 4 2-, NH 4 + and NO 3-. Particulate organic matter was estimated by multiplying OC by a conversion factor which corresponds to the organic molecular carbon weight per carbon weight. A conversion factor of 1.6 was chosen to be in accordance with other studies for Greek urban environments and Athens (Grivas et al., 212; Terzi et al., 21). The results reported on figure 4(a), show that SIA, OM and EC contribute in PM 2.5 mass about 33%(±9), 32%(±9) and 5%(±3) respectively justifying more than 7% of PM 2.5 mass. Figure 4(b) presents the contributions of SIA, dust, mineral fraction of anthropogenic origin (MIN) and sea salt (SS) determined in PTFE samples. From this figure, which also confirms SIA percentage shown in Figure 4(a) from quartz samples, it can be seen that dust contribution became significant in cases of Saharan dust transport events (12-5%) and was calculated to be about 3-5% in absence of dust events. The anthropogenic mineral fraction contribution was calculated to be about 3%. A mean value of 4% for sea salt contribution in PM 2.5 was calculated from the whole data set. These results are in agreement and confirm the results obtained in a previous study for the same sampling point for a shorter period of time (Remoundaki et al., 213a). Summarizing the above results, a quantitative estimation was possible of the main constituents of PM 2.5 from a significant data set. Secondary inorganic and carbonaceous component are the major constituents of PM 2.5 justifying over 7% of their mass while main natural sources and mineral anthropogenic dust contribute about 1-12% in the PM 2.5 mass in absence of African dust transport events. 4. CONCLUSIONS Results from a systematic monitoring of PM 2.5 concentrations and composition at an urban site in Athens (NTUA campus) have shown that secondary inorganic and carbonaceous fractions were the major constituents of PM 2.5 Secondary inorganic ions (sum of sulfates, nitrates and ammonium) concentrations represent 89% of the total mass of inorganic ions determined, (with sulfates being the most abundant: 65%) and were at the same level with those of organic matter. PM 2.5 concentrations did not presented significant seasonal variation. Sulfates concentrations increased during the summer months while nitrates presented the opposite pattern. EC concentrations were higher during the cold season than those observed for the warm season. Although the upward trend of OC concentrations during the months of April-July, pointing out that photochemically produced secondary OC becomes significant, organic carbon concentrations did not present a significant seasonal pattern and this is mainly due to the reduction of the primarily emitted OC during the summer months. The ratio OC/EC presented a significant seasonal pattern with higher values during the warm season. For the mass closure calculations, six components were considered: SIA, Organic Matter (OM), Elemental Carbon (EC), Dust, Mineral anthropogenic component (MIN) and Sea Salt (SS). SIA, OM and EC contribute in PM 2.5 mass about 33%(±9), 32%(±9) and 5%(±3) respectively representing a fraction greater than 7% of the PM 2.5 mass. Dust contribution became significant in cases of Saharan dust transport events (12-5%) and was calculated to be about 3-5% in absence of dust events. The anthropogenic mineral

7 fraction contribution was calculated to be about 3%. Finally, a mean value of 4% for sea salt contribution in PM 2.5 was calculated from the whole data set. SO 4 2- NH Concentration (ng/m 3 ) Concentration (ng/m 3 ) NO 3-14 Concentration (ng/m 3 ) OC (ng/m3) EC (ng/m3) OC/EC Concentration (ng/m 3 ) Figure 3. Mean monthly concentrations in ng/m 3 for sulfates, ammonium, nitrates, organic and elemental carbon and mean monthly values of the ratio OC/EC (a) % EC % OM % SIA (b) % contribution in PM /6/11 6/7/11 27/7/11 18/8/11 7/12/11 15/12/11 3/12/11 14/1/12 25/1/12 1/3/12 14/3/12 28/3/12 13/4/12 26/4/12 1/5/12 23/5/12 6/6/12 2/6/12 4/7/12 18/7/12 1/8/12 15/8/12 5/9/12 19/9/12 Date Figure 4. Percentage of (a) SIA, OM, EC and (b) SIA, dust, MIN and SS in PM 2.5 concentrations.

8 Acknowledgements The present study was financially supported by PEVE 21(Program for the Support of Basic Research) of the NTUA. The authors thank Dr. D. Vassilakopoulos for technical assistance with WDXRF analysis (School of Chemical Engineering, NTUA) and Dr. N. Xirokostas for technical assistance with ICP-MS analysis. REFERENCES 1. Gerasopoulos, E., Kouvarakis, G., Babasakalis, P., Vrekoussis, M., Putaud, J.P. & Mihalopoulos, N. (26) Origin and variability of particulate matter (PM1) mass concentrations over the Eastern Mediterranean, Atmos Environ, 4, Grivas, G., Chaloulakou, A. & Kassomenos, P. (28) An overview of the PM1 pollution problem, in the Metropolitan area of Athens, Greece. Assessment of controlling factors and potential impact of long range transport, Sci Total Environ, 389, Grivas, G., Cheristanidis, S. & Chaloulakou, A. (212) Elemental and organic carbon in the urban environment of Athens. Seasonal and diurnal variations and estimates of secondary organic carbon, Sci Total Environ, 414, Karageorgos, E.T. & Rapsomanikis, S. (27) Chemical characterization of the inorganic fraction of aerosols and mechanisms of the neutralization of atmospheric acidity in Athens, Greece, Atmos Chem Phys, 7, Koulouri, E., Saarikoski, S., Theodosi, C., Markaki, Z., Gerasopoulos, E., Kouvarakis, G., Makela, T., Hillamo, R. & Mihalopoulos, N. (28) Chemical composition and sources of fine and coarse aerosol particles in the Eastern Mediterranean, Atmos Environ, 42, Mihalopoulos, N., Kerminen, V.M., Kanakidou, M., Berresheim, H. & Sciare, J. (27) Formation of particulate sulfur species (sulfate and methanesulfonate) during summer over the Eastern Mediterranean: A modelling approach, Atmos Environ, 41, Remoundaki, E., Bourliva, A., Kokkalis, P., Mamouri, R.E., Papayannis, A., Grigoratos, T., Samara, C. & Tsezos, M. (211) PM(1) composition during an intense Saharan dust transport event over Athens (Greece), Sci Total Environ, 49, Remoundaki, E., Kassomenos, P., Mantas, E., Mihalopoulos, N. & Tsezos, M. (213a) Composition and mass closure of PM 2.5 in urban environment (Athens, Greece), Aerosol and Air Quality Research, 13, Remoundaki, E., Papayannis, A., Kassomenos, P., Mantas, E., Kokkalis, P. & Tsezos, M. (213b) Influence of Saharan dust transport events on PM 2.5 concentrations and composition over Athens during 21, Water, Air and Soil Pollution, 224, Sillanpaa, M., Hillamo, R., Saarikoski, S., Frey, A., Pennanen, A., Makkonen, U., Spolnik, Z., Van Grieken, R., Branis, M., Brunekreef, B., Chalbot, M.C., Kuhlbusch, T., Sunyer, J., Kerminen, V.M., Kulmala, M. & Salonen, R.O. (26) Chemical composition and mass closure of particulate matter at six urban sites in Europe, Atmos Environ, 4, S212-S Terzi, E., Argyropoulos, G., Bougatioti, A., Mihalopoulos, N., Nikolaou, K. & Samara, C. (21) Chemical composition and mass closure of ambient PM1 at urban sites, Atmos Environ, 44, Theodosi, C., Grivas, G., Zarmpas, P., Chaloulakou, A. & Mihalopoulos, N. (211) Mass and chemical composition of size-segregated aerosols (PM(1), PM(2.5), PM(1)) over Athens, Greece: local versus regional sources, Atmos Chem Phys, 11,