Non Methane Hydrocarbons variability in Athens during winter-time: The role of traffic and heating

Abstract

Abstract. Non-methane hydrocarbons (NMHCs) play an important role in atmospheric chemistry, contributing to ozone and secondary organic aerosol formation. They can also serve as tracers for various sources such as traffic, solvents, heating and 15 vegetation. The current work presents, for the first time to our knowledge, time-resolved, uninterrupted data of NMHCs, from two to six carbon atoms, during a period of five months (mid-October 2015 to mid-February 2016) in the Great Athens Area (GAA), Greece. The measured NMHC levels are among the highest reported in literature for the Mediterranean area and the majority of the compounds demonstrates a remarkable day to day variability. Their levels increase by up to factor of four from autumn (October-November) to winter (December-February). Local meteorology and especially wind speed seems 20 to control the variability of NMHC levels, with an increase up to a factor of 10 occurring under low wind speed (<3 m s -1 ), reflecting the impact of local sources rather than long range transport. All NMHCs demonstrated a pronounced bimodal, diurnal pattern with a morning peak followed by a second one before midnight. The amplitude (intensity) of both peaks is gradually increasing towards winter, respectively to autumn, by a factor of 3 to 6 and nicely follow that of carbon monoxide (CO), indicating contribution from additional sources e.g. heating. By comparing the NMHC diurnal variability with that of 25 black carbon (BC), its fractions associated with wood burning (BC wb ) and fossil fuel combustion (BC ff ), as well as with source profiles we conclude that the morning peak is attributed to traffic while the night one mainly to heating. However, the present data set does not allow for quantification of the relative contribution of fossil fuel and wood burning for heating purposes, although tracers and source profiles clearly indicate the presence of both sources.