Final Report: Remote Sensing of NO and NO2 Emissions from Heavy-Duty Diesel Trucks Using Tunable Diode LasersEPA Grant Number: R824794
Title: Remote Sensing of NO and NO2 Emissions from Heavy-Duty Diesel Trucks Using Tunable Diode Lasers
Investigators: McRae, Gregory J. , Jimenez, Jose-Luis , Kolb, Charles E. , Nelson, David D. , Zahniser, Mark S.
Institution: Massachusetts Institute of Technology , Aerodyne Research Inc.
EPA Project Officer: Chung, Serena
Project Period: October 1, 1995 through September 30, 1998
Project Amount: $388,284
RFA: Air Pollutants (1995) Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:On-road remote sensors can measure the emissions of motor vehicles under real-world conditions. The most sensitive and versatile remote sensor reported to date is based on Tunable Infrared Laser Differential Absorption Spectroscopy (TILDAS). This study applied this TILDAS remote sensor to the measurement of the emissions from heavy-duty diesel trucks (HDDTs). The remote sensor could operate with an optical pathlength of 88 m, or more than 5 times that of competing instruments. Remote sensing of NO2 emissions was demonstrated for the first time. Good agreement was obtained when comparing the TILDAS measurements with the on-board measurements of an instrumented HDDT. The distribution of NO emissions from HDDT was found not to be skewed. HDDTs are estimated to contribute about 375 of the on-road NOx emission inventory. These emissions are underestimated by a factor of 2.2 in the latest EPA inventory.
Emissions of oxides of nitrogen (NO and NO2, collectively referred to as NOX) are important for a variety of environmental problems, including photochemical smog, acid deposition, and the health and visibility impacts of fine particulate matter. As the NOx emissions of passenger cars and light-duty trucks have become increasingly controlled, the relative importance of heavy-duty diesel trucks and buses as a NOx source has increased. A recent assessment estimated heavy-duty diesel vehicles to contribute about _ of the on-road NOx inventory in the U.S.1 However, large uncertainties remain about the magnitude and the distribution of these emissions.1 For example a recent study found that California's emission inventory model may underestimate NOx emissions from heavy-duty diesel trucks (HDDTs) by up to a factor of 2.3.2
Recent developments highlight the increasing attention being given to these emissions. More stringent U.S. emission standards for heavy-duty diesel engines, which seek to reduce NOx emissions by about 50%, were enacted in 1997.3 In addition, EPA recently accused seven ma30r diesel engine manufacturers of disabling the NOx-control strategies on their engine control systems under highway cruise conditions in order to improve fuel economy, resulting on large increases on NOx emissions. This claim was settled with a total cost for the manufacturers in excess of $1 billion, including the largest civil penalty even for violation of environmental law ($83 million).4
The reduction of heavy-duty diesel NOx emissions remains difficult. Diesel engines use large amounts of excess air under all operating conditions, which results in stoichiometric or lean combustion conditions and the associated high NOx production.5 Post-combustion NOx removal is problematic. The three-way catalysts used for NOx reduction from light-duty vehicles do not reduce NOx to N2 when the exhaust O2 concentration is high.6 Lean-NOx catalysts, incorporating fuel hydrocarbons as the chemical reducing agent, are under very active research.7
The determination of accurate emission factors and inventory contributions for heavy duty diesel vehicles has received an increasing amount of attention in recent years.8-20 The information derived from these research programs is being used to design better emission control strategies.21
On-road remote sensing instruments can determine the emissions of passing cars by optical absorption measurements in the vehicle wake. Remote sensing of passenger car emissions was pioneered by Donald Stedman and Gary Bishop of the University of Denver using a Non-Dispersive Infrared (NDIR) technique.22, 23 Remote sensing of emissions from heavy duty diesel trucks were first reported by Bishop et al.24 A high precision remote sensor based on Tunable Infrared Laser Differential Absorption Spectrometry (TILDAS) has recently been developed and applied to the measurement of NO and N20 emissions from passenger cars and light-duty trucks.25, 26 This instrument is the most sensitive and versatile on-road remote sensor reported to date. This paper presents the results of a study in which the TILDAS technique was adapted to heavy-duty diesel truck emission remote sensing. The goals of this study were to demonstrate the feasibility of the application of this technique to HDDTs and to clarify some of the outstanding questions about their NOx emissions.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
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||Jimenez JL, McManus JB, Shorter JH, Nelson DD, Zahniser MS, Koplow M, McRae GJ, Kolb CE. Cross road and mobile tunable infrared laser measurements of nitrous oxide emissions from motor vehicles. Chemosphere-Global Change Science 2000;2(3-4):397-412.||
||Jimenez JL, Mcrae GJ, Nelson DD, Zahniser MS, Kolb CE. Remote sensing of NO and NO2 emissions from heavy-duty diesel trucks using tunable diode lasers. Environmental Science & Technology 2000; 34(12):2380-2387.||