Composition and variability of gaseous organic pollution in the port megacity of Istanbul: source attribution, emission ratios, and inventory evaluation
Authors: Thera Baye T. P. , Dominutti Pamela , Öztürk Fatma , Salameh Thérèse , Sauvage Stéphane , Afif Charbel , Çetin Banu , Gaimoz Cécile , Keleş Melek , Evan Stéphanie , Borbon Agnès 
Published: December 2019

Abstract. In the framework of the TRANSport Emissions and Mitigation in the East
Mediterranean (TRANSEMED/ChArMEx) program, volatile organic compound (VOC)
measurements were performed for the first time in Istanbul (Turkey) at an
urban site in September 2014. One commercial gas chromatograph coupled to a
flame ionization detector (GC–FID) and one proton transfer mass spectrometer
(PTR-MS) were deployed. In addition, sorbent tubes and canisters were
implemented within the megacity close to major emission sources. More than
70 species including non-methane hydrocarbons (NMHCs), oxygenated VOCs (OVOCs),
and organic compounds of intermediate volatility (IVOCs) have been
quantified. Among these compounds, 23 anthropogenic and biogenic species
were 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 between
0.1 (methacrolein + methyl vinyl ketone) and 4.9 ppb (methanol). OVOCs represent
43.9 % 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 Factorization
model (EPA PMF 5.0) and have been compared to source profiles established by
near-field measurements and other external variables (meteorological
parameters, NOx, CO, SO2, etc.). Surprisingly, road transport
is not the dominant source, only explaining 15.8 % of measured VOC
concentrations contrary to the local emission inventory. Other factors are
toluene from solvent use (14.2 %), biogenic terpenes (7.8 %), natural
gas evaporation (25.9 %) composed of butanes, and a last factor
characterized by mixed regional emissions and composed of most of the
species (36.3 %). The PMF model results point out the influence of industrial
emissions while there is no clear evidence of the impact of ship emissions
on the measured VOC distribution. For the latter additional measurements of
organic compounds of lower volatility like IVOC would be helpful. The
sensitivity of PMF results to input data (time resolution, meteorological
period, peak episode, interpolation method) was tested. While some PMF runs do not perform as well statistically as the reference run, sensitivity tests
show that the same factors (number and type) are found with slightly different
factor 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 other
cities worldwide but in the same range of magnitude. These ERs and the road
transport factor from PMF were used to estimate VOC emissions and to
evaluate three downscaled global emissions inventories (EDGAR, ACCMIP, and
MACCity). It was found that the total annual VOC anthropogenic emissions by
global inventories were either within the same range by a factor of 2 to
3 for alkanes and aromatics or underestimated by an order of magnitude,
especially for oxygenated VOCs.