Transportation: Trailer Refrigeration & More…

Diesel TRUs run at low engine loads and are frequently in Stop/Start mode, which promotes incomplete combustion and elevated diesel particulate matter (DPM) output. Unlike trucks that operate at steadier loads, TRU engines can emit up to 10 times more DPM than much larger, modern diesel truck engines.

Because TRUs are concentrated at distribution centers, loading docks, and retail delivery points, their emissions are disproportionately impactful in populated areas, making emission control a pressing operational and compliance concern.

Retrofitting your existing TRUs with a diesel particulate filter (DPF) is one of the most direct and cost-effective ways to reduce DPM emissions without replacing your equipment. A properly designed DPF captures soot from exhaust before it enters the atmosphere, significantly reducing particulate output while keeping refrigeration operations fully intact.

Retrofit costs typically run well below the cost of full unit replacement, making this approach practical for fleets managing tight budgets while facing tightening compliance requirements.

Take a closer look at how active DPF technology supports fleet transitions.

High-efficiency DPF systems can reduce diesel particulate matter emissions by up to 95%, including in the stop-and-go duty cycles typical of cold chain delivery routes. This level of reduction applies across a range of operating conditions, from urban distribution runs to extended dock-side idling.

See this article for a detailed look at the black carbon and particulate emissions profile of TRUs and how active DPF technology addresses them.

No. A DPF is installed in the engine exhaust system and has no connection to the refrigeration circuit, so it does not interfere with temperature setpoints, load protocols, or refrigeration performance. Your cold chain operating procedures remain completely unchanged.

The most immediate step is retrofitting existing TRUs with verified diesel particulate filters, which can capture up to 95% of DPM at the source without disrupting cold chain operations or delivery schedules. Beyond retrofits, fleets can also monitor engine performance and maintenance schedules, implement cleaner fuel strategies where available, incorporate lower-emission units into future procurement decisions, and align reductions with broader sustainability goals.

For more, see these strategies to help retail grocery and food distribution operations reduce their environmental impact.

An active DPF uses an onboard heating element to initiate regeneration on a scheduled basis, burning off accumulated soot regardless of exhaust temperature. This is critical for TRUs, which run at low loads and rarely generate the exhaust heat needed for passive regeneration on their own.

Because the regeneration process is automated and independent of duty cycle, drivers do not need to adjust their routines, and refrigeration setpoints are not affected.

Yes. DPFs designed for transport refrigeration units can be verified by the California Air Resources Board (CARB) to meet the Ultra-Low Emission TRU (ULETRU) particulate matter standard of 0.02 g/bhp-hr. CARB verification requires independent testing and confirms the system consistently reduces particulate emissions to compliant levels under real-world operating conditions.

Fleets operating CARB-verified DPF systems can meet ULETRU requirements while continuing to use their existing TRU equipment. Click here for a practical breakdown of the compliance and operational reasons to install a DPF.

Most TRUs on the market can be retrofitted with a diesel particulate filter. Rypos currently offers retrofit DPF systems compatible with Thermo King and Carrier trailer refrigeration units, covering a large share of fleets in operation today. Some units may be incompatible or may already meet applicable emissions standards without a retrofit.

Contact Rypos directly with your specific fleet details to confirm compatibility and identify the right system for your application.

Rypos DPF systems use active regeneration to continuously burn off accumulated soot, which means the filter itself never needs to be replaced or removed for routine service. This is a key advantage of active DPF technology over passive systems, which may require periodic physical cleaning or filter changeouts.

CARB-verified ULETRU DPFs provide ongoing, evergreen compliance with CARB requirements as long as the TRU is registered in the ARBER system and carries a current CARB decal on the unit housing. There is no compliance expiration tied to the DPF itself, provided the system continues to perform to its verified specification and registration remains current.

Yes. Even without California’s specific regulatory requirements, TRU emissions concentrated at a facility can have measurable health consequences for employees working at and around loading docks and staging areas. Diesel particulate matter is classified as a toxic air contaminant, and high-exposure environments like distribution centers warrant attention regardless of state.

Beyond employee health, organizations in all states face growing expectations from customers, partners, and investors around emissions reporting and reduction. Reducing DPM from your TRU fleet is one of the more direct ways to address emissions in a cold chain operation.