Three decades of on-road mobile source emissions reductions in South Los Angeles

Abstract

In May 2018, the University of Denver repeated on-road optical remote sensing measurements at two locations in Lynwood, CA. Lynwood area vehicle tailpipe emissions were first surveyed in 1989 and 1991 because the area suffered from a large number of carbon monoxide (CO) air quality violations. These new measurements allow for the estimation of fuel-specific CO and total hydrocarbon (HC) emissions reductions, changes in the longevity of emission-control components, and the prevalence of high emitters in the current fleet. Since 1989 CO emissions decreased approximately factors of 10 (120 ± 8 to 12.3 ± 0.2 gCO/kg of fuel) and 20 (210 ± 8 to 10.4 ± 0.4 gCO/kg of fuel) at our I-710/Imperial Highway and Long Beach Blvd. sites, respectively. These reductions are also reflected in the local ambient air measurements. Tailpipe HC emissions have decreased by a factor of 25 (50 ± 4 to 2.1 ± 0.3 gHC/kg of fuel) since 1991 at the Long Beach Blvd. location. The decreases are so dramatic that the vast majority of vehicles now have HC measurements that are indistinguishable from zero. The decreases have increased the skewedness of the emissions distribution with the 99th percentile now responsible for more than 37% (CO) and 28% (HC) of the totals. Ammonia emissions collected in 2018 at both Lynwood locations peak with 20-year-old vehicles (1998 models), indicating long lifetimes for catalytic converters. In 1989 and 1991, the on-road Lynwood fleets had significantly higher emissions than fleets observed in other locations within the South Coast Air Basin. The 2018 fleets now have means and emissions by model year that are consistent with those observed at other sites in Los Angeles and the U.S. This indicates that modern vehicle combustion management and after-treatment systems are achieving their goals regardless of community income levels. Implications: Recent on-road vehicle emission measurements at two locations in the Lynwood, CA area, first visited in 1989, found significant fuel specific CO and HC emission reductions. CO emissions have decreased by a factor of 10 and 20 at each location and HC emissions have declined by a factor of 25. This has increased the skewedness in both species emissions distribution. The 2018 fleets have means and emissions by model year that are now consistent with those observed at other U.S. sites indicating that modern vehicle emissions control advancements are achieving their goals regardless of community income levels.

Leveraging Citizen Science and Low-Cost Sensors to Characterize Air Pollution Exposure of Disadvantaged Communities in Southern California

“…Lynwood (north of our study area) showed the highest average concentrations and larger variations compared with the lowest values in San Pedro (south of our study area); this result is presumably attributable to the fact that our monitored household in Lynwood was located between westbound I-710 and southbound I-105, two of the major highways in the area. This finding suggests that Lynwood may be heavily impacted by on-road mobile source emissions over time, consistent with the finding of another local study [ 38 ]. While San Pedro is located near the Port of LA, a study has found that freeway emissions were the major sources of PM 2.5 and had much higher emission rates (2–5 times) compared with sources at the Port of LA [ 39 ].…”

Large Decreases in Tailpipe Criteria Pollutant Emissions from the U.S. Light-Duty Vehicle Fleet Expected in 2020–2040

“…As shown in Figures and and Figure S2, dramatic progress has been made over the past 20 years in reducing criteria pollutant emissions from the U.S. on-road light duty vehicle fleet, and this progress is expected to continue over the next 20 years. This is a continuation of the trend of reduced emissions from the ICEV fleet over the past 60 years. − , The downward trend of absolute emissions in Figure is even more impressive compared to the concurrent increases in vehicle stock and vehicle miles traveled (Figure ). Separate from the introduction of new ICEVs with modern emission control technology and lower criteria pollutant emissions, a large-scale transition to BEVs is underway in the automotive industry.…”

The Influence of Seasonal Climate Variability on Vehicle Exhaust PM2.5 in the State of California: A Hybrid Approach based on Artificial Neural Network and Spatial Analysis

“…This is because the study's focus was PM2.5 from vehicle emissions, and to the date, there has not been any direct measurement available for car emissions. The only available data was Don Stedman's group at the University of Denver [23] but, the temporal and spatial resolution of this data was not enough to serve the purpose of this study.…”