Vehicle Exhaust Remote Sensing Device Method to Screen Vehicles for Evaporative Running Loss Emissions

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Automotive Engineering

Background:

• Vehicle emissions contribute to air pollution, with both tailpipe and non-tailpipe sources.
• Understanding the apportionment of hydrocarbon (HC) emissions is crucial for effective air pollution control policies.
• Evaporative emissions, particularly running losses, represent a significant non-tailpipe source.

Purpose of the Study:

• To develop and apply a method for detecting evaporative running loss emissions using roadside exhaust sensors.
• To estimate the fleet-wide prevalence of evaporative running loss emissions.
• To identify vehicle types most associated with these emissions.

Main Methods:

• Utilized roadside exhaust sensor data measuring hydrocarbon (HC) and carbon dioxide (CO2).
• Defined a running loss index (RLI) based on the 90th percentile of HC/CO2 correlation residuals.
• Screened vehicle emission databases from West Los Angeles (2013, 2015) using the RLI method, identifying measurements exceeding three standard deviations above instrument noise.

Main Results:

• The RLI method successfully identified potential evaporative running loss emissions.
• An estimated 0.09% (2013) and 0.18% (2015) of measurements indicated evaporative running loss.
• California LEV I certified vehicles (1994-2003) were the predominant age group associated with these emissions.
• Instrument detection limits were significantly higher than federal standards.

Conclusions:

• Roadside exhaust sensors can be adapted to detect non-tailpipe evaporative HC emissions.
• Evaporative running loss emissions, though infrequent, are detectable in real-world vehicle fleets.
• Older vehicle fleets, specifically California LEV I models, show a higher propensity for these emissions, informing targeted policy interventions.