Abstract
Continuous measurements of a wide range of non-methane hydrocarbons (NMHC) have been performed since 2001 in Paris megacity and three French medium-sized cities (Grenoble, Marseille, and Strasbourg). After a careful verification of the data measured, the ambient concentrations are used to analyze the spatial and seasonal variability of the anthropogenic NMHC and determine the present NMHC emission ratios relative to acetylene, a useful metric to evaluate and constraint emission inventories. We show that NMHC urban composition is consistent between all cities with no industrial influence and characteristic of the urban emission mixtures, which are mostly dominated by vehicle exhaust emissions. In winter, the urban NMHC composition generally shows an enhancement in combustion-derived products (alkenes, acetylene), C2–C3 alkanes and benzene, which presumes seasonal changes in emission ratio values. Present emission ratios of NMHC relative to acetylene are determined in Paris and Strasbourg both in summer and winter. They generally compare within a factor of two except for C7–C9 aromatics in Paris. On a seasonal basis, summertime emission ratios are three times higher than wintertime ones while they stay constant for combustion derived product (alkenes) and benzene. The unburned gasoline fraction (alkanes and C7–C9 aromatics) shows the maximum difference up to a factor of seven. These findings suggest that the emission ratios reflect seasonal changes in emissions and can be a useful metric to constraint temporally resolved emission inventories at different time of the year.
Highlights
Volatile organic compounds (VOC) are important chemical constituents of urban air pollution, as precursors of tropospheric ozone (O3) (Seinfeld, 1989) and secondary organic aerosols (SOA) (e.g. Odum et al, 1997; Kroll and Seinfeld, 2008)
We show that non-methane hydrocarbons (NMHC) urban composition is consistent between all cities with no industrial influence and characteristic of the urban emission mixtures, which are mostly dominated by vehicle exhaust emissions
While on a global scale VOC emissions are dominated by biogenic sources (Guenther et al, 2006), in most urban areas the anthropogenic emissions are the principal contributor to NMHC sources
Summary
Volatile organic compounds (VOC) are important chemical constituents of urban air pollution, as precursors of tropospheric ozone (O3) (Seinfeld, 1989) and secondary organic aerosols (SOA) (e.g. Odum et al, 1997; Kroll and Seinfeld, 2008). Volatile organic compounds (VOC) are important chemical constituents of urban air pollution, as precursors of tropospheric ozone (O3) (Seinfeld, 1989) and secondary organic aerosols (SOA) Several papers have shown the importance of VOC emissions on both ozone and SOA formation through air quality modeling studies Non-methane Hydrocarbons (NMHC), a subset of VOC, are emitted by both anthropogenic and biogenic sources. While on a global scale VOC emissions are dominated by biogenic sources (Guenther et al, 2006), in most urban areas the anthropogenic emissions are the principal contributor to NMHC sources. NMHC can be separated into several classes including alkanes associated with the incomplete combustion of tailpipe emissions and fuel evaporation from vehicles and gas stations (Watson et al, 2001); aromatics found as components of vehicle exhaust, fuel evaporation and solvent use; alkenes and alkynes mainly associated with combustion processes. Note that lighter alkanes (C2eC4) are components of natural gas and liquefied petroleum gas (LPG) (Harley et al, 1992; Blake and Rowland, 1995; Chen et al, 2001)
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