This is the catalytic converter. You may notice that it is about a foot-and-a-half longer than the average import car’s converter. This is not because the Insight emits more that most cars. Just the opposite. The Insight runs a very lean air-to-fuel ratio, about 25% leaner than other cars. When very lean mixtures are used, the engine will produce more NOx emissions. NOx contributes to the orange hazy smog we see on sunny days. This converter reduces HC, CO, and NOx as do all converters on modern cars, but in addition it is also designed to absorb and store NOx during times when the internal combustion engine is running lean. At times, the IC engine control unit will cause the mixture to go rich in order to reduce and release the NOx being stored in the converter. This keeps the overall NOx emissions low.