Control Technology-Driven Changes to In-Use Heavy-Duty Diesel Truck Emissions of Nitrogenous Species and Related Environmental Impacts

• Published in: Environmental science & technology 2019-12, Vol.53 (24), p.14568-14576
• Main Authors: Preble, Chelsea V, Harley, Robert A, Kirchstetter, Thomas W
• Format: Article
• Language: English
• Subjects: Air Pollutants; Ammonia; Automotive engines; Black carbon; byproducts; Carbon dioxide; Carbon dioxide emissions; catalytic reactions; Climate change; Diesel; Emission standards; Environment; Environmental effects; Environmental impact; Environmental Monitoring; environmental pollution; ENVIRONMENTAL SCIENCES; Global warming; Motor Vehicles; Nitrogen; Nitrogen dioxide; Nitrogen oxides; Nitrous oxide; Oxides; Photochemicals; Redox reactions; San Francisco; Selective catalytic reduction; Trucks; Vehicle Emissions
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.9b04763

Emissions from thousands of in-use heavy-duty diesel trucks were sampled at a highway and an arterial street location in the San Francisco Bay Area, spanning a time period when use of diesel particle filters (DPFs) and selective catalytic reduction (SCR) increased rapidly. At the highway site where a diverse mix of trucks is observed, SCR systems on 2010 and newer engines reduce emitted nitrogen oxides (NO x ) by 87 ± 5% relative to pre-2004 engines. SCR also mitigates DPF-related increases in nitrogen dioxide (NO2) emissions. However, a majority of trucks had in-use NO x emission rates that exceeded applicable emission standards. SCR systems increase emissions of nitrous oxide (N2O) and ammonia (NH3) from near-zero levels to 0.93 ± 0.13 and 0.18 ± 0.07 g kg–1, respectively. Emissions of all nitrogenous species and especially NH3 are skewed; 10% of trucks contribute 95% of the on-road fleet’s total NH3 emissions. Similar emission changes are observed at the arterial street site where exclusively drayage trucks operate. The environmental effects of decreased black carbon, NO x , and carbon dioxide (CO2) emissions and increased N2O and NH3 emissions due to the rapid adoption of DPF and SCR systems by the California truck fleet are: (1) a 65% net decrease in the social cost of statewide exposure to diesel truck emissions (−3.3 billion 2018 US dollars per year), and (2) a 3% net decrease in the global warming potential-weighted emission factor (−27 g CO2-eq km–1).