Quantification of Self Pollution from Two Diesel School Buses using Three Independent Methods

Area of Science:

• Environmental Science
• Air Quality Research
• Transportation Emissions

Background:

• School buses contribute to air pollution, impacting passenger health.
• Understanding self-pollution (SP) within buses is crucial for assessing exposure.
• Particulate matter (PM) and its constituents are key indicators of air quality.

Purpose of the Study:

• To quantify self-pollution (SP) inside school buses using multiple methods.
• To identify the primary sources of SP, specifically tailpipe and crankcase emissions.
• To compare the effectiveness of different monitoring techniques for in-cabin air quality.

Main Methods:

• Monitoring of particulate matter (PM) and constituents (EC/OC, particle counts) inside buses and a lead vehicle (LV).
• Utilized three distinct methods: dual tracers (DT), lead vehicle (LV), and chemical mass balance (CMB).
• Collected source samples from tailpipe and crankcase emissions using an on-board dilution tunnel.

Main Results:

• In-cabin PM concentrations were higher than in the LV.
• Dual tracer (DT) method estimated significant contributions from tailpipe (1.1 µg/m³) and crankcase (6.8 µg/m³) emissions.
• Crankcase emissions were identified as the dominant SP source, particularly with windows closed.

Conclusions:

• Three independent methods confirmed significant self-pollution (SP) in school buses.
• Crankcase emissions represent the major contributor to in-cabin particulate matter (PM).
• Further calibration of lead vehicle (LV) measurements is needed for precise SP quantification.