Effects of Retrofitting Emission Control Systems on In-Use Heavy Diesel Vehicles

Abstract

Diesel engines are now the largest source of nitrogen oxides (NO x ) and fine particulate black carbon (soot) emissions in California. The California Air Resources Board recently adopted a rule requiring that by 2014 all in-use heavy trucks and buses meet current (2007) exhaust particulate matter (PM) emission standards. Also by 2023 all in-use heavy-duty vehicles will have to meet current NO x emission standards, with significant progress in achieving the requirements for NO x control expected by 2014. This will require retrofit or replacement of older in-use engines. Diesel particle filters (DPF) reduce PM emissions but may increase the NO 2 /NO x emission ratio to ∼35%, compared to ∼5% typical of diesel engines without particle filters. Additionally, DPF with high oxidative capacity reduce CO and hydrocarbon emissions. We evaluate the effects of retrofitting trucks with DPF on air quality in southern California, using an Eulerian photochemical air quality model. Compared to a 2014 reference scenario without the retrofit program, black carbon concentrations decreased by 12 ( 2% and 14 ( 2% during summer and fall, respectively, with corresponding increases in ambient ozone concentrations of 3 ( 2% and 7 ( 3%. NO 2 concentrations decreased by 2-4% overall despite the increase in primary NO 2 emissions because total NO x emissions were reduced as part of the program to retrofit NO x control systems on in-use engines. However, in some cases NO 2 concentrations may increase at locations with high diesel truck traffic.

On the observed response of ozone to NO<sub>x</sub> and VOC reactivity reductions in San Joaquin Valley California 1995–present

“…NO x abundances across California have fallen at near constant rates over the last decade; this is consistent with our understanding of trends in emissions (Cox et al, 2009;Millstein and Harley, 2010;Dallmann and Harley, 2010) and supported by surface measurements (Ban-Weiss et al, 2008;Lafranchi et al, 2011;Parrish et al, 2011) and space-based observations (Kim et al, 2009;Russell et al, 2010Russell et al, , 2012. These NO x decreases have had led to striking improvements in ozone air quality in the Sacramento Valley (Lafranchi et al, 2011) but less so in the Los Angeles basin, where chemistry remains NO x -suppressed and the dramatic improvements of the 1980's and 1990's have slowed (e.g.…”

“…In California, in an effort to expedite benefits from new diesel engine regulations, the California Air Resources Board (CARB) is requiring all vehicle owners to retrofit or replace older diesel engines by 2023 and half of the in-use heavy duty-engines in large fleets must meet new NO x standards by 2014 (California Air Resources Board, 2007). Millstein and Harley (2010) show that in Los Angeles, as a result of this accelerated engine retrofit/replacement program, reductions in summertime diesel NO x emissions could be greater than 50 % over the five years from 2010 to 2015, with slower reductions (-20 % in tons day −1 ) predicted in the following ten years from 2015 to 2025. Additionally, the SJV Air Pollution Control District is also partnering with the Environmental Protection Agency (EPA) under the National Clean Diesel Campaign to replace diesel locomotives and diesel engines on agricultural equipment (Environmental Protection Agency, 2012a).…”

“…In the SJV, NO x is typically 30-50 % lower on weekends than weekdays, a phenomenon largely due to reduced weekend heavyduty diesel truck traffic (e.g. Marr et al, 2002b;Millstein and Harley, 2010). Meteorological and chemical conditions, such as VOCR, are far less day-of-week dependent than are changes in NO x and, as a result, comparison of weekdays to weekends is an effective and widely used tool to study the NO x dependence of O 3 formation (e.g.…”

“…At many locations there are reports of decreases in organic emissions (e.g. Environmental Protection Agency, 2003;Parrish, 2006;Bishop and Stedman, 2008;Monks et al, 2009;Wilson et al, 2012) but changes to the total organic reactivity are not well documented. These precursor changes are predicted to have substantially affected the photochemical ozone production rate and thus the probability of exceeding health-based standards.…”

Radical precursors and related species from traffic as observed and modeled at an urban highway junction

“…The main reason for this increase is considered to be the use of diesel oxidation catalysts (DOCs) and catalyzed diesel particulate filters (DPFs) (Bar-Ilan et al, 2010;Bishop et al, 2010), which became standard equipment on new diesel trucks starting with 2007 (Ban- Weiss et al, 2008; see also: http://www.epa.gov/oms/highwaydiesel/). These exhaust-treatment systems may enhance NO 2 fraction in NO x emission up to 70% (Alvarez et al, 2008;Millstein and Harley, 2010).…”