Abstract
We investigate the composition of 63 C2-C10 nonmethane hydrocarbons (NMHCs), methane (CH4) and carbon monoxide (CO), in Jeddah, Mecca, and Madina (Saudi Arabia), in Lahore, (Pakistan), and in Singapore. We established a database with which to compare and contrast NMHCs in regions where ambient levels and emissions are poorly characterized, but where conditions are favorable to the formation of tropospheric ozone, and where measurements are essential for improving emission inventories and modeling. This dataset will also serve as a base for further analysis of air pollution in Western Saudi Arabia including, but not limited to, the estimation of urban emissions and long range pollution transport from these regions. The measured species showed enhanced levels in all Saudi Arabian cities compared to the local background but were generally much lower than in Lahore. In Madina, vehicle exhaust was the dominant NMHC source, as indicated by enhanced levels of combustion products and by the good correlation between NMHCs and CO, while in Jeddah and Mecca a combination of sources needs to be considered. Very high NMHC levels were measured in Lahore, and elevated levels of CH4 in Lahore were attributed to natural gas. When we compared our results with 2010 emissions from the MACCity global inventory, we found discrepancies in the relative contribution of NMHCs between the measurements and the inventory. In all cities, alkenes (especially ethene and propene) dominated the hydroxyl radical (OH) reactivity (k OH) because of their great abundance and their relatively fast reaction rates with OH.
Highlights
Nonmethane hydrocarbons (NMHCs) are an important component of volatile organic compounds (VOCs)
Similar to the data set collected in Saudi Arabia, we observe a high variability in the ambient mixing ratios measured in Lahore and Singapore, which is characteristic of urban environments where emission sources, transport/mixing, boundary layer fluctuations and diurnal variability in photochemistry all contribute to the observed NMHC levels
The ground-based samples collected in October–November 2012 and April 2013 in Jeddah, Mecca, and Madina were analyzed for carbon monoxide (CO), CH4, and a large suite of NMHCs and compared to the local background and to samples collected around the same period in Lahore and Singapore
Summary
Nonmethane hydrocarbons (NMHCs) are an important component of volatile organic compounds (VOCs). To determine the relative importance of the different hydrocarbons toward O3 production, a detailed speciation of NMHCs in urban areas is needed For this reason, in the present study we characterize the composition of carbon monoxide (CO), methane (CH4), and NMHCs in the urban atmosphere of three cities in Saudi Arabia and we compare them with the tropospheric composition of two other Asian urban centers, namely Lahore (Pakistan) and Singapore. The NMHC composition from the Saudi Arabian urban areas was compared to data gathered in Lahore (samples collected from December 29 and 31, 2012) and Singapore (August–October, 2012 sampling) This comparison has two main purposes: to characterize and compare the NMHC profiles in different Asian cities and to expand the NMHC data sets currently available for populated cities in Asia, in order to improve existing emission inventories. Ground-based measurements are essential for improving emission inventories that characterize surface emissions used in air quality modeling
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