An analysis of real-world exhaust emission control deterioration in the California light-duty gasoline vehicle fleet

Abstract

The understanding of vehicle exhaust emission control deterioration is important for developing accurate emission inventories and for evaluating emission reduction regulation effectiveness. We show that a common practice of conducting deterioration analysis for multiple-model-year groups may produce unrealistic deterioration rates, because the samples' model year constitution usually varies with age. As a more reliable approach, we analyze the deterioration for individual model years. We apply this approach to light-duty gasoline vehicle exhaust emission measurements conducted using remote sensing devices at a West Los Angeles location during seven campaigns between 1999 and 2015. Vehicles of 1985–1993 model years (termed herein as “pre-LEV” model years for predating California's Low-Emission Vehicle regulations), most of them older than 10 years when sampled, did not exhibit strong and consistent deterioration with age for carbon monoxide (CO) and hydrocarbon (HC) emissions, whereas their nitric oxide (NO) emissions appeared to deteriorate approximately linearly with age. The 1994–2003 model-year vehicles, subject to California's original Low-Emission Vehicle standards (LEV I standards) and up to about 20 years old when sampled, deteriorated approximately linearly with age for the three species. Our limited measurement records for the 2004–2014 model-year vehicles, subject to California's second-generation Low-Emission Vehicle standards (LEV II standards) and up to about 10 years old when sampled, did not exhibit consistent deterioration with age. Here we propose an empirical model to describe those deterioration patterns for the pre-LEV and LEV I vehicles.