Abstract
In the efforts at controlling automobile emissions, it is important to know in what extent air pollutants from on-road vehicles could be truly reduced. In 2014 we conducted tests in a heavily trafficked tunnel in south China to characterize emissions of volatile organic compounds (VOC) from on-road vehicle fleet and compared our results with those obtained in the same tunnel in 2004. Alkanes, aromatics, and alkenes had average emission factors (EFs) of 338, 63, and 42mgkm-1 in 2014 against that of 194, 129, and 160mgkm-1 in 2004, respectively. In 2014, LPG-related propane, n-butane and i-butane were the top three non-methane hydrocarbons (NMHCs) with EFs of 184±21, 53±6 and 31±3mgkm-1; the gasoline evaporation marker i-pentane had an average EF of 17±3mgkm-1; ethylene and propene were the top two alkenes with average EFs of 16±1 and 9.7±0.9mgkm-1, respectively; isoprene had no direct emission from vehicles; toluene showed the highest EF of 11±2mgkm-1 among the aromatics; and acetylene had an average EF of 7±1mgkm-1. While EFs of total NMHCs decreased only 9% from 493±120mgkm-1 in 2004 to 449±40mgkm-1 in 2014, their total ozone formation potential (OFP) decreased by 57% from 2.50×103mgkm-1 in 2004 to 1.10×103mgkm-1 in 2014, and their total secondary organic aerosol formation potential (SOAFP) decreased by 50% from 50mgkm-1 in 2004 to 25mgkm-1 in 2014. The large drop in ozone and SOA formation potentials could be explained by reduced emissions of reactive alkenes and aromatics, due largely to fuel transition from gasoline/diesel to LPG for taxis/buses and upgraded vehicle emission standards.
Highlights
Volatile organic compounds (VOCs) are precursors of tropospheric ozone and secondary organic aerosols (SOA) (Carter, 1994; Finlayson-Pitts and Pitts, 1999; Atkinson and Arey, 2003)
With the fast changing vehicle numbers and fleet compositions, vehicle emission standards and fuel quality in the last decade, it is important to see what really happened to the vehicle emission, and to get up-to-date emission factors
As tunnel measurement has its advantages to obtain absolute emission levels by capturing a snap-shot of the on-road vehicle fleet and representing real-world operation conditions, in 2014 we carried out measurements in the Zhujiang Tunnel, a busy tunnel with over 40,000 motor vehicles passing through in each direction per day in urban Guangzhou, and compared the results for speciated VOC emissions with that obtained in the same tunnel in 2004
Summary
Volatile organic compounds (VOCs) are precursors of tropospheric ozone and secondary organic aerosols (SOA) (Carter, 1994; Finlayson-Pitts and Pitts, 1999; Atkinson and Arey, 2003). They are emitted from both biogenic and anthropogenic sources. In the Pearl River Delta (PRD) region of the South China, bottom-up estimates suggest that motor vehicles contribute to 40e57% of VOCs from anthropogenic emission sources (Zhang et al, 2009; Zheng et al, 2009b; Che et al, 2011; Lu et al, 2013). Field measurements in the PRD region have demonstrated that vehicle exhaust may constitute 20e53% of anthropogenic VOCs (Guo et al, 2007a; Liu et al, 2008b; Zhang et al, 2012, 2013; Ling et al, 2011) and 24e40% of the ozone formation potentials (OFPs) (Zheng et al, 2009a; Cheng et al, 2010; Zhang et al, 2012)
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