Long-term variability, source apportionment and spectral properties of black carbon at an urban background site in Athens, Greece. (1st February 2020)

• Record Type: Journal Article
• Authors: Liakakou, E.; Stavroulas, I.; Kaskaoutis, D.G.; Grivas, G.; Paraskevopoulou, D.; Dumka, U.C.; Tsagkaraki, M.; Bougiatioti, A.; Oikonomou, K.; Sciare, J.; Gerasopoulos, E.; Mihalopoulos, N.
• Is Part Of: Atmospheric environment. Volume 222(2020)
• Publication Date: 2020-02-01
• Subjects: Black carbon -- Wood burning -- Source apportionment -- Mixing layer -- Biomass burning tracers -- Athens; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2019.117137
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: This study aims to delineate the characteristics of Black Carbon (BC) in the atmosphere over Athens, Greece, using 4-year (May 2015–April 2019) Aethalometer (AE-33) measurements. The average BC concentration is 1.9 ± 2.5 μg m −3 (ranging from 0.1 to 32.7 μg m −3 ; hourly values), with a well-defined seasonality from 1.3 ± 1.1 μg m −3 in summer to 3.0 ± 4.0 μg m −3 in winter. Pronounced morning and evening/night peaks are found in the BC concentrations in winter, while during the rest of the seasons, this diurnal cycle appears to flatten out, with the exception of the morning traffic peak. On an annual basis, the biomass-burning fraction (BB%) of BC accounts for 22 ± 12%, while the fossil-fuel combustion (BCff ) component (traffic emissions and domestic heating) dominates during summer (83%) and in the morning hours. BCwb exhibits higher contribution in winter (32%), especially during the night hours (39%). BC levels are effectively reduced by precipitation, while they significantly build-up for wind speeds <3 m s −1 and mixing-layer height (MLH) < 500 m. Normalizing the BC diurnal course by the MLH variations on a seasonal basis reveals that the residential wood-burning emissions are mostly responsible for the large BC increase during winter nights, whereas the low BC levels during daytime in the warm season are mainly attributed to dilution into a deeper MLH. BCwb is highly correlated with other BB tracers during winter nights (e.g. levoglucosan, non-sea-salt-K +, m/z 60 fragment), as well as with the fine fraction (PM2.5 ) OC and EC. The Delta-C, which represents the spectral dependence of BC as the absorption difference between 370 and 880 nm, is analyzed for the first time in Athens. It exhibits a pronounced seasonality with maximum values in winter night-time, and it appears as a valid qualitative marker for wood combustion. Highlights: 4-years assessment of BC concentrations and emission sources in Athens. Biomass-burning tracers justify the high wood-burning emissions in winter. The winter-time residential wood-burning persists during the study period. Remarkable effects of low wind speed and mixing-layer height in BC levels. Equal BC contribution from fossil fuel and wood burning during winter nights.