ABB LGR | Emissions of Ammonia and Other Nitrogen-Containing Volatile Organic Compounds from Motor V

Emissions of Ammonia and Other Nitrogen-Containing Volatile Organic Compounds 

from Motor Vehicles under Low-Speed Driving Conditions

Ammonia (NH₃) and amines are major alkaline gases in the atmosphere. Despite their relatively low ambient concentrations (a few ppbv for NH₃ and several pptv for amines), these trace gases can significantly impact atmospheric chemical processes. Globally, agriculture-related activities and anthropogenic sources are recognized as the important NH₃ source. And recent field studies found that motor vehicles are also a potential source of amines that could be responsible for the enhanced nucleation events in Beijing, China. As organic derivatives of NH₃, amines often share with NH₃ their source profiles, but the magnitude of amine emissions is still unknown. In light of the drastically increased personal car ownership in China, motor vehicles are expected to play a progressively more important role in primary air pollutant emissions, particularly in urban environments. Therefore, an in-depth investigation of vehicular emissions of NH₃ and amines is of practical importance for formulating air pollution abatement strategies.

Based on this, in this study, a group of Chinese scientists deployed a water-cluster chemical ionization mass spectrometer along with other trace gas monitors on the roadside of the campus of Nanjing University Information Science and Technology (NUIST; N32°12′27″, E118°42′31″) to characterize individual in-use motor vehicle’s emission ratios (ER) for NH₃ and nine amine-derived nitrogen-containing volatile organic compounds (NVOCs) that contain 1 to 3 carbon atoms (i.e., C₁₋₃-amines, C₁₋₃-imines, and C₁₋₃- amides). These results are analyzed to identify the individual emission profiles of gasoline-powered passenger cars (GP), diesel-powered light-duty trucks (DT), and natural-gas powered taxis (NT).

Among the other trace gas monitors, the concentration of carbon dioxide (CO₂) was measured with a commercial instrument (Los Gatos Research, LGR), which can simultaneously detect dry mixing ratios of CO₂, methane (CH₄), and water vapor based on a fourth-generation cavity enhanced absorption technique. CO₂ within the vehicle exhausts was measured at a time resolution of 10 Hz with a noise level of 1.4 ppmv. Given the typical high concentrations of CO₂ within the exhaust (∼1000 ppmv), the uncertainty associated with CO₂ measurements is around 0.1%.

[Results]:

 The total emission strength of diesel trucks was the greatest followed by those of gasoline cars and natural gas cars. NH3 emission per vehicle was found to be 2−3 orders of magnitude greater than that of all NVOCs, regardless of the type of vehicle. Although much lower than the emissions of amides or imines, emissions of amines were sufficient to produce atmospheric concentrations exceeding the threshold level for amines to enhance atmospheric nucleation by several orders of magnitude. Different engine emission reduction technologies (e.g., three-way catalytic converter vs selective catalytic reduction) can lead to different NH3 and NVOC emission profiles. During the lifetime of a vehicle, its emission level was most likely to increase with its mileage. Source profiles of NH3 and NVOC emissions from the three types of vehicles were also obtained from the measurements.

Table 1. Summary of Emission Ratios (avg ± σ) of NH₃ and NVOCs for: Gasoline-Powered Passenger Cars (GP), Diesel-Powered Light-Duty Trucks (DT), and Natural Gas-Powered Taxis (NT).

Figure 2. Emission profiles of GP, DT, and NT vehicles obtained from the mass spectra generated by the water cluster-CIMS. The statistics shown in the legend are based on a sample space of 63 GP, 14 DT, and 12 NT vehicles, respectively.

Figure 3. Emission ratios of NH₃ and NVOCs of gasoline-powered passenger cars segmented by vehicle mileage (panel a), years in service (panel b), and emission standards implemented (panel c), that is, Chinese national standard IV (China IV) and V (China V), respectively.

[Conclusion]:

The authors concluded that these profiles can be a valuable contribution to the air pollution management system in terms of source apportionment, elucidating the emission contributions from a specific type of vehicle.