Long-term characterization of organic and elemental carbon in the PM2.5 fraction: the case of Athens, Greece.

Organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and main ions were measured in a total of 1510 PM_2.5 daily aerosol samples collected from May 2008 to April 2013 in Athens, Greece. OC and EC concentrations were 2.1 ± 1.3 μgm^-3 and 0.54 ± 0.39 μgm^-3 , accounting for 11 ± 3 % and 3 ± 1 % of PM2.5 mass, respectively, with an average OC / EC ratio of 4.7 ± 3.1. Significant correlation was found between OC and EC during the whole period, indicating emissions by common primary sources on a regional scale. WSOC concentration ranged from 0.03 to 10.6pgm^-3 , with an average of 1.5 ± 0.9 μgm^-3 . By considering the Finokalia (Crete) station as a reference, it was estimated that, during the warm season in Athens, 67 ± 7% of emitted OC and 53 ± 12% of emitted EC is regional, while, during cold months, the regional contribution of OC is only 33 ± 7 % and of EC 29 ± 8 %. Furthermore, secondary organic carbon (SOC) was calculated for the warm period of the year (April to October). The estimated SOC constituted about 75 ± 6 % of PM_2.5 organic carbon in Athens, highlighting significant aging processes on a regional scale. In the period 2011-2013 and during wintertime, an increase in OC and EC levels was observed, attributed to an increase in wood burning for domestic heating due to the economic crisis. [ABSTRACT FROM AUTHOR]