Emission Characteristics and Factors of Fine Particulate Nitrated Phenols from Various On-road Vehicles

Abstract:

Nitrated phenols, which are recognized as important components of brown carbon, can strongly absorb near-UV light and visible light, and thus affect the radiation balance and further influence the regional climate. In addition, nitrated phenols also harm plant growth and human health. Nitrated phenols in the atmosphere originate from the primary emissions of combustion processes and the secondary formation from aromatic precursors. Vehicle exhaust has been supposed to be one of the major emission sources of nitrated phenols, however, there is a lack of comprehensive understanding on the direct emissions of nitrated phenols from various motor vehicles.

In this study, a mobile measurement system was deployed to collect fine particulate samples and to measure the related pollutants and parameters from the exhausts of eight passenger vehicles, eight trucks, and two taxis under real driving conditions. The test vehicles were classified by vehicle load, i.e., light-duty, medium-duty, and heavy-duty, and fuel types, e. g., diesel, gasoline, and compressed natural gas. Then twelve nitrated phenols collected in the fine particulate samples from various vehicles exhaust were detected using ultrahigh performance liquid chromatography-mass spectrometry. Finally, the emission characteristics, profiles, and factors of fine particulate nitrated phenols were determined, and the emission amounts of various vehicles in China were estimated.

The results show that the concentrations and emission profiles of fine particulate nitrated phenols varied with vehicle load and fuel type. The 4-nitrophenol and its methyl derivatives were the dominant nitrated phenol species from vehicle exhausts. The emission factors also exhibited large variations across vehicle type, fuel type and emission standards, with relatively low values for gasoline vehicles and taxis fueled by compressed natural gas and high values for diesel vehicles. This work highlights the high emission level of nitrated phenols from diesel vehicles and provides an essential basis for atmospheric modeling and effective pollution control.