Clean Air Task Force Investigations of School Bus Engine Crankcase Emissions and Controls

The document reports that engine crankcase emissions are the primary source of PM2.5 mass in conventional school bus cabins, while the tailpipe is the main source of ultrafine particles, black carbon, and particulate polycyclic aromatic hydrocarbons. Research across four US cities indicates that while diesel particulate filters (DPFs) and ultra-low sulfur diesel (ULSD) reduce ultrafines and black carbon to ambient levels, they do not significantly reduce PM2.5. The installation of a closed-crankcase filtration device, specifically the Donaldson Spiracle™, was found to be critical and necessary to reduce cabin PM2.5 levels to near ambient levels across all tested bus and fuel combinations.

• The engine crankcase is identified as the largest source of PM2.5 mass affecting the interior air quality of conventional school buses, with emissions entering the cabin from below the door.
• Tailpipe emissions are the primary source of ultrafine particles, black carbon, and particulate polycyclic aromatic hydrocarbons (PPAH) in the cabin, though they contribute little to no PM2.5 mass.
• Retrofitting buses with diesel particulate filters (DPFs) and using ultra-low sulfur diesel (ULSD) effectively reduces ultrafines, black carbon, and PPAH to ambient levels, but fails to substantially reduce PM2.5 mass.
• The use of a closed-crankcase filtration device, specifically the Donaldson Spiracle™, is the only method tested that consistently reduces cabin PM2.5 to near ambient levels, regardless of other retrofits or fuel types used.

APA

Hill, L. B. (2006). Clean Air Task Force Investigations of School Bus Engine Crankcase Emissions and Controls. Clean Air Task Force. https://cdn.catf.us/wp-content/uploads/2019/10/21093425/Diesel_Crankcase_Emissions_and_Controls.pdf

Chicago

Hill, L. B. Clean Air Task Force Investigations of School Bus Engine Crankcase Emissions and Controls. Clean Air Task Force, 2006. https://cdn.catf.us/wp-content/uploads/2019/10/21093425/Diesel_Crankcase_Emissions_and_Controls.pdf.

Wikipedia

{{cite report |last1=Hill |first1=L. B. |title=Clean Air Task Force Investigations of School Bus Engine Crankcase Emissions and Controls |publisher=Clean Air Task Force |date=30 January 2006 |url=https://cdn.catf.us/wp-content/uploads/2019/10/21093425/Diesel_Crankcase_Emissions_and_Controls.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{hill2006clean, author = {Hill, L. B.}, title = {{Clean Air Task Force Investigations of School Bus Engine Crankcase Emissions and Controls}}, institution = {Clean Air Task Force}, year = {2006}, month = jan, url = {https://cdn.catf.us/wp-content/uploads/2019/10/21093425/Diesel_Crankcase_Emissions_and_Controls.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }