Question

Under what specific regulatory condition is a Portable Emission Measurement System (PEMS) required to supplement laboratory testing for real-world compliance?

Accepted Answer

A Portable Emission Measurement System, or PEMS, is required to supplement laboratory testing when a vehicle manufacturer must demonstrate compliance with Real Driving Emissions, or RDE, regulations. Laboratory testing occurs under controlled conditions on a chassis dynamometer, which is a stationary treadmill for cars that simulates driving patterns. Because laboratory tests cannot capture every variable of the real world, regulators require PEMS to ensure vehicles remain clean during actual road usage. A PEMS is a set of portable sensors and analyzers installed on the back of a vehicle to measure tailpipe pollutants like nitrogen oxides and carbon monoxide while the car is driven on public roads. The specific regulatory condition triggering this requirement is the need to close the gap between controlled laboratory results and the actual emissions performance observed during daily operation, accounting for factors like varying traffic, altitude, ambient temperatures, and aggressive driving styles that stationary equipment cannot replicate.

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Under what specific regulatory condition is a Portable Emission Measurement System (PEMS) required to supplement laboratory testing for real-world compliance?