Application of a Diffusion Charger to Quantify Real-Time Particle Emissions from Light-Duty Vehicles: a Comparison Study with a Particle Size Spectrometer

Measurement methods for vehicle-emitted particulate matter (PM) have evolved as vehicle emission standards have become more stringent. For example, the filter-based gravimetric method has been demonstrated feasible to measure emissions at levels below 1 mg/mi from light-duty vehicles. However, while regulatory methods and instruments for measuring PM emissions are rigorous and accurate, there is a need to continue evaluating alternatives for use in the laboratory, as well as simple and robust instruments for screening that can be used for detecting high emissions on the roadside and evaluating the effectiveness of repairs in support of inspection and maintenance (I/M) programs. This study investigated the performance of an aerosol diffusion charger (TSI Electrical Aerosol Detector) by comparing its raw signal (aerosol active surface area) and its conversion to particle number and mass emission rates with those reported or calculated from a multi-channel electrometer-based particle size spectrometer (TSI Engine Exhaust Particle Sizer) and various condensation particle counters (CPCs). Four light-duty vehicles were tested, including gasoline port fuel injection (PFI), gasoline direct injection (GDI), and a diesel vehicle equipped with a diesel particulate filter (DPF). Results show that the diffusion charger was responsive over a wide particle size and concentration range, exhibiting sufficient signal-to-noise ratio during transient measurements of the gasoline PFI vehicle and light-duty diesel vehicle with a DPF (both certified below 1 mg/mi). High sensitivity at low concentrations suggests that the diffusion charger may have potential for identifying failures of emission control systems at lower concentrations than methods designed to report real-time suspended particle number or mass metrics directly. Systematic and fundamental data from our study underscore the challenge with “black box” equipment calibrated to calculate total particle number and mass from surface area measurements based on constant unimodal fit parameters. Future work could focus on the applications from deploying active surface area monitors at the roadside or for using surface area measurements to evaluate repair effective in support of I/M programs.