Secondary Particulate Matter Exceed Primary Emissions from Current Gasoline Vehicles: Air Quality and Public Health Implications

A comprehensive study on the effects of photochemical aging on exhaust emissions from a vehicle equipped with a gasoline direct injection engine when operated over seven different driving cycles was assessed using an oxidation flow reactor. Both primary emissions and secondary aerosol production were measured over the Federal Test Procedure, LA92, New European Driving Cycle, US06, and the Highway Fuel Economy Test, as well as over two real-world cycles developed by the California Department of Transportation mimicking typical highway driving conditions. The research team showed that the emissions of primary particles were largely dependent on cold-start conditions and acceleration events. Secondary organic aerosol (SOA) formation also exhibited strong dependence on the cold-start cycles and correlated well with SOA precursor emissions (i.e., non-methane hydrocarbons [NMHCs]) during both cold-start and hot-start cycles (correlation coefficients 0.95–0.99), with overall emissions of about 68–94 mg SOA per g NMHC. SOA formation significantly dropped during the hot-running phases of the cycles, with simultaneous increases in nitrate and ammonium formation as a result of the higher nitrogen oxide (NOx) and ammonia emissions. The findings suggest that more SOA will be produced during congested, slow-speed, and braking events in highways. Fuel type and composition also affect tailpipe emissions and secondary aerosol production from mobile sources. Therefore, the researchers assessed the influence of gasoline fuels with varying levels of aromatics and ethanol on the primary emissions and secondary aerosol formation from a flexible fuel vehicle equipped with a port fuel injection engine. The vehicle was exercised over the LA92 and US06 driving cycles using a chassis dynamometer. Secondary aerosol formation potential was measured using a fast oxidation flow reactor. Results showed that the high-aromatic fuels led to higher gaseous-regulated emissions, as well as particulate matter, black carbon, and total and solid particle number. The high ethanol content fuel (E78) resulted in reductions for the gaseous-regulated pollutants and particulate emissions. Secondary aerosol formation potential was dominated by the cold-start phase and increased for the high aromatic fuel. Secondary aerosol formation was seen in lower levels for E78 due to the lower formation of precursor emissions using this fuel. In addition, operating driving conditions and aftertreatment efficiency played a major role on secondary organic and inorganic aerosol formation, indicating that fuel properties, driving conditions, and exhaust aftertreatment should be considered when evaluating the emissions of secondary aerosol precursors from mobile sources.

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Supplemental Notes:
- This document was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
Corporate Authors:
Center for Advancing Research in Transportation Emissions, Energy, and Health (CARTEEH)

,

Office of the Assistant Secretary for Research and Technology

University Transportation Centers Program
Department of Transportation
Washington, DC United States 20590
Authors:
- Karavalakis, Georgios
- 0000-0001-5011-8371
Publication Date: 2021-4

Language

English

Media Info

Media Type: Digital/other
Edition: Final Report

Subject/Index Terms

TRT Terms: Aerosols; Air quality; Exhaust gases; Gasoline engines; Particulates; Public health
Subject Areas: Environment; Highways; Society;

Filing Info

Accession Number: 01789292
Record Type: Publication
Report/Paper Numbers: UCD-01-14
Contract Numbers: 69A3551747128
Files: UTC, NTL, TRIS, ATRI, USDOT
Created Date: Nov 23 2021 9:01AM