Emissions of nitrogen oxides and volatile organic compounds from liquefied petroleum gas-fueled taxis under idle and cruising modes.

Liquefied petroleum gas (LPG) as an alternative fuel is increasingly used in mainland China, few reports are however available about emissions from LPG-fueled vehicles. In this study, 26 LPG-fueled taxis in Guangzhou, south China were tested using a chassis dynamometer to obtain their emission factors of nitrogen oxides (NO) and volatile organic compounds (VOCs) under idle and cruising (10-60 km h) modes. The emission factors of NO on average increased with speed from 4.13 g kg-fuel at idling to 71.1 g kg-fuel at 60 km h at a slope of 10.6 g kg-fuel per 10 km h increase in speed. Alkanes were the most abundant (71.9%) among the VOCs in the exhaust, followed by alkenes (25.2%), ethyne (2.7%), and aromatic species (0.2%). Emission factors of VOCs at idling averaged 8.24 g kg-fuel, higher than that of 6.23-7.36 g kg-fuel when cruising at 10-60 km h, but their ozone formation potentials (OFPs) were lower at idling (15.8 g kg-fuel) than under cruising (19.1-23.8 g kg-fuel) largely due to higher emission of more reactive alkenes under cruising mode. Emissions of both NOx and VOCs increased significantly with mileages. Measured emission factors of NO and reactive VOCs in this study suggested that replacing the gasoline-powered taxis with the LPG-fueled taxis with LPG-gasoline bi-fuel engines and no efficient after-treatment devices would not benefit in reducing the emissions of ozone precursors, and strengthening the emission control for LPG vehicles with dedicated LPG engines and after-treatment converters, as did in Hong Kong, could further benefit in reducing the emission of photochemically active species when using LPG as alternative fuels.