Mixing ratios of volatile organic compounds (VOCs) in the atmosphere of Karachi, Pakistan

Abstract

Mixing ratios of carbon monoxide (CO), methane (CH 4), non-methane hydrocarbons, halocarbons and alkyl nitrates (a total of 72 species) were determined for 78 whole air samples collected during the winter of 1998-1999 in Karachi, Pakistan. This is the first time that volatile organic compound (VOC) levels in Karachi have been extensively characterized. The overall air quality of the urban environment was determined using air samples collected at six locations throughout Karachi. Methane (6.3 ppmv) and ethane (93 ppbv) levels in Karachi were found to be much higher than in other cities that have been studied. The very high CH 4 levels highlight the importance of natural gas leakage in Karachi. The leakage of liquefied petroleum gas contributes to elevated propane and butane levels in Karachi, although the propane and butane burdens were lower than in other cities (e.g., Mexico City, Santiago). High levels of benzene (0.3-19 ppbv) also appear to be of concern in the Karachi urban area. Vehicular emissions were characterized using air samples collected along the busiest thoroughfare of the city (M.A. Jinnah Road). Emissions from vehicular exhaust were found to be the main source of many of the hydrocarbons reported here. Significant levels of isoprene (1.2 ppbv) were detected at the roadside, and vehicular exhaust is estimated to account for about 20% of the isoprene observed in Karachi. 1,2-Dichloroethane, a lead scavenger added to leaded fuel, was also emitted by cars. The photochemical production of ozone (O 3) was calculated for CO and the various VOCs using the Maximum Incremental Reactivity (MIR) scale. Based on the MIR scale, the leading contributors to O 3 production in Karachi are ethene, CO, propene, m-xylene and toluene.

Source attributions of hazardous aromatic hydrocarbons in urban, suburban and rural areas in the Pearl River Delta (PRD) region

“…These ratios consistent with the ratio observed in urban Guangzhou in 2005 (0.41, [5]), but lower than the ratio from boreal forest fire (0.80) [66]. Benzene, as a carcinogenic compound forbidden to be used in industry, were mainly from automobile exhausts in urban areas [5,24,64], so dominant contribution from vehicle exhausts in the urban site GEMC explained the higher benzene/acetylene ratio than at other sites [5,28]. As toluene, C 8 -aromatics and C 9 -aromatics were widely used as solvents in painting, coating, printing and cleaning processes in the highly industrialized PRD region [3,26,33,67], their high ratios to acetylene at WQS suggested substantial contribution of AHs from industrial emissions in the upwind city of Dongguan, a worldknown manufacturing center in the region.…”

“…Acetylene, for example, had been used extensively as a tracer for combustion [4,28,[60][61][62][63][64][65], and the ratios of hydrocarbons to acetylene were widely used to examine the impact of other emissions sources relative to combustion emissions. The ratios of propane, n-butane and i-butane to acetylene, for example, have been used to indicate their contribution from LPG leakage [28,60].…”

“…The first source is solvent use which is characterized by a significant amount of aromatics species and n-hexane which are major components in various solvents commonly used in manufacturing industries, such as n-hexane in electronics industry particularly the PRD region [3,67]. Source 2 is considered to be LPG/LNG related emissions with a dominance of propane, isobutene, n-butane and ethane, which are typical tracer of emission from LPG/LNG [5,64]. Vehicle exhaust is identified as source 3 by a significant presence of acetylene, C 3 -C 4 alkanes, and aromatics [36].…”

Species profiles and normalized reactivity of volatile organic compounds from gasoline evaporation in China

“…In the present study, benzene ranged 0.71e1.37% in refueling vapors and averaged 0.44% in headspace vapors; the latter was comparable to that of 0.37% reported by Harley et al (2000) or 0.56% by Na et al (2004) in headspace vapors, but much lower than that of 4.49% previously reported in China by Liu et al (2008a). Table 2 presents ratios of paired VOCs that have been widely used to indicate relative contributions from different emission sources (Barletta et al, 2002(Barletta et al, ,2008Jobson et al, 2004;Chan et al, 2006;de Gouw et al, 2006;Karl et al, 2007;Simpson et al, 2011). Toluene to benzene (T/B) ratios ranged 2.0e5.8 in refueling vapors from the present study, and ranged 1.5e6.5 in headspace vapors from this study and previous works (Harley et al, 2000;Na et al, 2004;Liu et al, 2008a).…”

Emission profiles of carbonyl compounds at a Brazilian charcoal plant

“…[2][3][4] These compounds are of great concern not only because they are ozone precursors, but also because some of them are carcinogenic chemicals. 5 The carbonyl compounds have been attracting much attention because of their adverse health effects.…”