LAUSR

Abstract This study aims to characterize the variability and sources of water-soluble organic nitrogen (WSON), in aerosol over Cyprus in the Eastern Mediterranean. Measurements of PM10 particles were conducted during the calendar year of 2011 at two sites, located at a roadside location in Nicosia (urban traffic) and in the rural area of Agia Marina Xyliatou (regional background). Filter samples were analyzed for water-soluble total nitrogen (WSTN), nitrate and ammonium, to determine WSON. Additional analyses were performed, for water-soluble organic carbon (WSOC), organic and elemental carbon (OC and EC), major ions and trace metals. Annual mean WSON concentrations of 0.20 and 0.16 μgN m-3 were determined at the urban traffic and regional background sites, respectively. The organic fraction of WSTN was about 20%, with limited inter-site and seasonal variability. Distinct seasonal patterns were observed at the two sites, with warm-period concentrations being significantly higher at the regional background site, while the enhanced local emissions during winter at the traffic site smoothed out the observed variability. Mean WSON/WSOC ratios of 0.09-0.12 were calculated at the two sites, with the two parameters being weakly correlated. A roadside WSON enhancement was verified, although moderate on an annual basis (9%). However, concentrations in Nicosia were more than one time higher than the background during winter. The observed temporal and inter-site variability highlighted the necessity of source apportionment, which was performed using Positive Matrix Factorization (PMF) modeling, utilizing the analytical datasets at the two sites. In this way, the estimated contribution of regional transport of processed aerosols was found to be more pronounced at the regional background site (59% vs. 38%), while a sizeable input (35%) was linked to vehicular emissions at the traffic site. An additional anthropogenic impact, probably related to biomass burning, was estimated at both sites (16%), while contributions of natural sources like mineral dust (4-8%) and marine aerosol (2-3%) were smaller.