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. In the framework of the TRANSport Emissions and Mitigation in the EastMediterranean (TRANSEMED/ChArMEx) program, volatile organic compound (VOC)measurements were performed for the first time in Istanbul (Turkey) at anurban site in September 2014. One commercial gas chromatograph coupled to aflame ionization detector (GC–FID) and one proton transfer mass spectrometer(PTR-MS) were deployed. In addition, sorbent tubes and canisters wereimplemented within the megacity close to major emission sources. More than70 species including non-methane hydrocarbons (NMHCs), oxygenated VOCs (OVOCs),and organic compounds of intermediate volatility (IVOCs) have beenquantified. Among these compounds, 23 anthropogenic and biogenic specieswere continuously collected at the urban site. VOC concentrations show a great variability with maxima exceeding 10 ppb(i.e., n-butane, toluene, methanol, and acetaldehyde) and mean values between0.1 (methacrolein + methyl vinyl ketone) and 4.9 ppb (methanol). OVOCs represent43.9 % of the total VOC concentrations followed by alkanes (26.3 %),aromatic compounds (20.7 %), alkenes (4.8 %), terpenes(3.4 %), and acetonitrile (0.8 %). Five factors have been extracted from the Positive Matrix Factorizationmodel (EPA PMF 5.0) and have been compared to source profiles established bynear-field measurements and other external variables (meteorologicalparameters, NOx, CO, SO2, etc.). Surprisingly, road transportis not the dominant source, only explaining 15.8 % of measured VOCconcentrations contrary to the local emission inventory. Other factors aretoluene from solvent use (14.2 %), biogenic terpenes (7.8 %), naturalgas evaporation (25.9 %) composed of butanes, and a last factorcharacterized by mixed regional emissions and composed of most of thespecies (36.3 %). The PMF model results point out the influence of industrialemissions while there is no clear evidence of the impact of ship emissionson the measured VOC distribution. For the latter additional measurements oforganic compounds of lower volatility like IVOC would be helpful. Thesensitivity of PMF results to input data (time resolution, meteorologicalperiod, peak episode, interpolation method) was tested. While some PMF runs do not perform as well statistically as the reference run, sensitivity testsshow that the same factors (number and type) are found with slightly differentfactor contributions (up to 16 % of change). Finally, the emission ratios (ERs) of VOCs relative to carbon monoxide (CO)were established. These ratios are usually higher than the ones of othercities worldwide but in the same range of magnitude. These ERs and the roadtransport factor from PMF were used to estimate VOC emissions and toevaluate three downscaled global emissions inventories (EDGAR, ACCMIP, andMACCity). It was found that the total annual VOC anthropogenic emissions byglobal inventories were either within the same range by a factor of 2 to3 for alkanes and aromatics or underestimated by an order of magnitude,especially for oxygenated VOCs.

atmospheric chemistry and physics

Composition and variability of gaseous organic pollution in the port megacity of Istanbul: source attribution, emission ratios, and inventory evaluation