Exploring the seasonal NMHC distribution in an urban area of the Middle East during ECOCEM campaigns: very high loadings dominated by local emissions and dynamics

Abstract

Environmental context Non-methane hydrocarbons play an important role in the formation of photochemical oxidants such as ozone. We investigate factors controlling the distribution of non-methane hydrocarbons in an urban area of the Middle East. The study highlights the importance of local emissions and atmospheric dynamics, and the limited effect of photochemistry at the measurement site. Abstract Measurements of over 70 C2-C16 non-methane hydrocarbons (NMHCs) were conducted in suburban Beirut (1.3 million inhabitants) in summer 2011 and winter 2012 during the Emission and Chemistry of Organic Carbon in the East Mediterranean (ECOCEM) field campaign. The levels of NMHCs observed exceeded by a factor of two in total volume the levels found in northern mid-latitude megacities (Paris and Los Angeles), especially for the unburned fossil fuel fraction. Regardless of the season, the major compounds, explaining 50% of the concentrations, were toluene, isopentane, butane, m,p-xylenes, propane and ethylene, emitted by mobile traffic and gasoline evaporation sources. Most NMHCs show a distinct seasonal cycle, with a summer maximum and a winter minimum, unlike seasonal cycles usually observed in the northern mid-latitude urban areas. We show that NMHC distribution is mainly driven by strong local emissions and local atmospheric dynamics, with no clear evidence of photochemical removal in summer or influence from long-range transport.

Source apportionment vs. emission inventories of non-methane hydrocarbons (NMHC) in an urban area of the Middle East: local and global perspectives

“…A certified NPL (National Physical Laboratory) standard of NMHC mixture (∼ 4 ppbv) was used to determine and check the stability of the GC carbon response during both measurement periods. The data have been published in Salameh et al (2015).…”

“…The wind direction was mostly from the northeast and slightly from south, southwest at night. During the winter measurement campaign, the temperature ranged from 7 to 22 • C with an average of 13 • C. The average wind speed was 2 m s −1 and the wind direction was mostly coming southeasterly and easterly (Salameh et al, 2015).…”

“…By taking into consideration the different existing reactivities, mainly with OH radical within the NMHC species, the profile of each source may change temporally during transport of emission plumes. Nevertheless, we have examined the factors influencing the distribution of NMHCs (Salameh et al, 2015) and we concluded that NMHCs were freshly emitted from local sources in winter but also in summer, and the chemical losses of NMHC species, even for the most reactive species, were likely not significant.…”

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

“…with long-term observations is possible only with Beirut (Salameh et al, 2015) and Bilbao (Durana et al, 2006). The levels observed in Athens are significantly higher even by more than 100%, with the exception of propane, butanes and toluene for Beirut and n-butane, benzene and toluene for Bilbao, which are quite similar to Athens.…”

“…NMHCs' oxidation contributes to the formation of secondary organic aerosols (SOA), which in turn affects light scattering, visibility and CCN formation (Tsigaridis and Kanakidou, 2003;Seinfeld and Pandis, 2016 and references therein). They mainly originate from anthropogenic sources such as traffic, solvents' use, residential heating, natural gas use, industrial activity, but also emit from natural sources such as vegetation (Guenther et al, 1995;Barletta et al, 2005;Kansal, 2009;Sauvage et al, 5 2009;Salameh et al, 2015;Baudic et al, 2016b;Jaimes-Palomera et al, 2016). Besides their key role as secondary pollutants precursors, NMHCs are of interest regarding their association with health issues (EEA report, N o 28/2016(EEA report, N o 28/ , 2016.…”