Abstract
Ambient mass concentrations of benzene and toluene were measured at 12 different road junctions of Ahmedabad city in India during the pre-monsoon season of year 2015. A Thermal Desorption-Gas Chromatography-Flame Ionization Detector (TD-GC-FID) technique was used for the analysis of aromatic volatile organic compounds (VOCs) in air samples. In each of both inner and outer ring roads, air samples were collected at 6 sites to investigate the spatial variation of benzene and toluene. The mass concentrations of benzene and toluene show strong site-to-site and day-to-day variations. The average mass concentration of benzene varied in the ranges of 11-35 μg m^(-3) and 4-12 μg m^(-3) along the inner and outer roads, respectively. The mass concentration of toluene varied in the ranges of 43-142 μg m^(-3) and 11-28 μg m^(-3) along the inner and outer roads, respectively. Overall, the mass concentrations of VOCs along the inner road were 3-5 times higher than those measured along the outer road.The mass concentrations of benzene and toluene show good correlation suggesting their common emission sources (mostly vehicular). However, the enhancement ratios of ΔToluene/ΔBenzene (~4.0 μg μg^(-1)) along both the roads were higher than the typical ratios (1.5-3.5 μg μg^(-1)) reported for vehicular emissions. The higher values of ΔToluene/ΔBenzene are due to the emissions of VOCs also from industrial and other non-traffic sources. During the daytime, the lower mass concentrations of VOCs and lower ΔToluene/ΔBenzene (~2 μg μg^(-1)) indicate the role of photochemical aging. The combined diurnal trend of ΔToluene/ΔBenzene agrees well with that measured at central Ahmedabad using the proton-transfer-reaction time of flight mass spectrometer (PTR-TOF-MS). However, compared to weekdays, the mass concentrations of VOCs show reduction and increase during the Sunday and Saturday, respectively. The mass concentration of VOCs and their ratio were towards the higher side of data reported for different urban sites of the world.
Highlights
In the global atmosphere, volatile organic compounds (VOCs) are ubiquitous and play important role in the earth’s environment and climate change (Velasco et al, 2008)
VOCs are emitted from a variety of both natural and anthropogenic sources, their predominant contribution varies from the region to region (Goldstein and Galbally, 2007)
Photo-oxidation of VOCs leads to the production of simple and multifunctional oxygenated-VOCs (OVOCs) which are transformed to secondary organic aerosols (SOA) through gas-particle partitioning (Seinfeld and Pandis, 2006)
Summary
Volatile organic compounds (VOCs) are ubiquitous and play important role in the earth’s environment and climate change (Velasco et al, 2008). Relevant to the rural regions of developing countries, the incomplete combustion of biomass burning and biofuel are still important source of VOCs (Sahu and Lal, 2006a, Sahu et al, 2015). The increasing level of VOCs and relatively faster consumption of OH can significantly reduce the oxidation capacity of the atmosphere. Most VOCs that are very reactive can significantly affect the radical chemistry including the heterogeneous interactions. VOCs are important precursors of ground-level ozone (O3) production in the presence of NOx (= NO + NO2) and sunlight (Sahu et al, 2013; Yadav et al, 2014; Yadav et al, 2016). Longterm exposure to the high concentrations of such VOCs above the permissible exposure limits can cause acute and chronic
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