Experimental Assessment of NOx Emissions from 73 Euro 6 Diesel

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Experimental assessment of NO emissions from 73 Euro 6 diesel passenger cars Liuhanzi Yang, Vicente Franco, Peter Mock, Reinhard Kolke, Shaojun Zhang, Ye Wu, and John German Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b04242 • Publication Date (Web): 18 Nov 2015 Downloaded from http://pubs.acs.org on November 21, 2015

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Environmental Science & Technology

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Experimental assessment of NOX emissions from 73

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Euro 6 diesel passenger cars

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Liuhanzi Yang a, b, c, Vicente Franco *, b, Peter Mock b, Reinhard Kolke d, Shaojun Zhang e, Ye Wu

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a, f

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a

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Control, Tsinghua University, Beijing 100084, China

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b

International Council on Clean Transportation Europe, Berlin 10178, Germany

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c

Higher Institute for Environmental Engineering and Management (ISIGE), MINES Paris Tech,

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Fontainebleau 77305, France

John German g

School of Environment, State Key Joint Laboratory of Environment Simulation and Pollution

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d

ADAC e.V., Technik Zentrum, Landsberg am Lech 86899, Germany

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e

Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109,

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USA

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f

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Complex, Beijing 100084, China

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g

State Environmental Protection Key Laboratory of Sources and Control of Air Pollution

International Council on Clean Transportation, Washington DC 20005, USA

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ABSTRACT

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Controlling nitrogen oxides (NOX) emissions from diesel passenger cars during real-world

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driving is one of the major technical challenges facing diesel auto manufacturers. Three main

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technologies are available for this purpose: exhaust gas recirculation (EGR), lean-burn NOX traps

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(LNT) and selective catalytic reduction (SCR). Seventy-three Euro 6 diesel passenger cars (8

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EGR-only, 40 LNT and 25 SCR) were tested on a chassis dynamometer over both the European

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type-approval cycle (NEDC, cold engine start) and the more realistic Worldwide Harmonized

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Light-duty Test Cycle (WLTC version 2.0, hot start) between 2012 and 2015. Most vehicles met

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the legislative limit of 0.08 g/km of NOX over NEDC (average emission factors by technology:

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EGR-only 0.07 g/km, LNT 0.04 g/km, SCR 0.05 g/km), but the average emission factors rose

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dramatically over WLTC (EGR-only 0.17 g/km, LNT 0.21 g/km, SCR 0.13 g/km). Five LNT-

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equipped vehicles exhibited very poor performance over the WLTC, emitting seven to 15 times

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the regulated limit. These results illustrate how diesel NOX emissions are not properly controlled

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under the current, NEDC-based homologation framework. The upcoming real-driving emissions

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(RDE) regulation, which mandates an additional on-road emissions test for EU type approvals,

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could be a step in the right direction to address this problem.

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ACS Paragon Plus Environment

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INTRODUCTION

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Nitrogen oxides (NOX) emissions from diesel passenger cars remain one of the largest

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contributors to urban air quality problems in Europe.1 Since the phase-in of the Euro 6 standard

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in the European Union (EU) in September 2014, all newly type-approved diesel passenger cars

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must meet a NOX emission limit of 0.080 g/km over the European vehicle emission certification

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cycle (New European Driving Cycle, NEDC), down from 0.180 g/km for the Euro 5 standard.2

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This increase in stringency should help alleviate the urban air quality problem in Europe.

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However, several previous studies have shown that vehicle emissions during “real-world”

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driving can be substantially higher than the values certified from chassis dynamometer

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laboratory measurements at type approval.3–10 In particular, studies based on portable emissions

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measurement systems (PEMS) have shown that on-road NOX emissions from modern diesel

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passenger cars can exceed the certified emission limit by a factor of more than 20, and average

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on-road emission factors (EFs) have been estimated to be about six to seven times the regulated

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Euro 6 limit.11–14 The results of comprehensive remote sensing (roadside emission measurements)

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studies in the UK indicate that NOX emissions from diesel vehicles have not decreased in line

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with the expectations set by the Euro emission standards, even for vehicles equipped with after-

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treatment systems especially designed to reduce NOX.15,16 In addition, new model diesel cars

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(Euro 3-5) under high engine loads have a NOX/CO2 (carbon dioxide) ratio double that of older-

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model cars.16 This large discrepancy between real-world emissions and laboratory tests is

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attributed to the shortcomings of current laboratory type-approval procedures, especially the

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failure of the NEDC procedure to realistically represent on-road driving conditions.5,8,17,18 In

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response to this problem, the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) was

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developed at the United Nations level and recently adopted by the United Nations Economic


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Commission for Europe (UNECE).19 In the EU, preparations are ongoing to replace the NEDC

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test procedure with the Worldwide Harmonized Light Vehicles Test Procedure (WLTP, which is

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built around the WLTC cycle and includes more robust provisions for the determination of test

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weight and chassis dynamometer road loads) from 2017 on.8,20,21 In addition, in May 2015, the

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European Commission approved the real-driving emissions (RDE) regulation (to be adopted in

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2016), whereby an on-road test using PEMS will be added as a mandatory requirement for the

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emissions type approval of passenger cars in the EU.22 Once RDE is implemented, passenger

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cars will have to demonstrate reasonably low emissions during conditions that resemble real-

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world use more closely than laboratory cycles. This could have a significant impact on the

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hardware choices made by diesel car manufacturers, and likely will lead to more robust

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implementations of NOX control technologies and to a long-term improvement in urban air

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quality in Europe.

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Three main technologies for NOX control are available on the market: inner-engine

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modifications coupled with exhaust gas recirculation (EGR), lean-burn NOX traps (LNT) and

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selective catalytic reduction (SCR). EGR systems work by rerouting a fraction of exhaust gas to

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the combustion chamber, lowering the combustion temperature and the production of engine-out

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NOX. EGR use has been widespread from Euro 4 to Euro 6 since the 1990s and can be used

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alone or in combination with LNT and SCR.11 One of the limitations of relying solely on EGR is

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the difficulty of controlling NOX emissions during high-load operation.23 In an LNT system,

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NOX is adsorbed to a catalyst during lean engine operation, then the stored NOX is periodically

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reduced during short periods of fuel-rich operation (LNT regeneration events). LNT has shown

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good durability and NOX reduction efficiency in chassis dynamometer tests.24 A major advantage

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of LNTs is that no tank is required to store reductant fluid (thus eliminating the need for periodic


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refills), so they are lighter and more compact than SCR systems. LNT systems have a high

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incremental cost per liter of engine displacement associated to increased used of platinum group

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metals (PGMs). Thus, small LNTs are generally more economical than SCR systems for

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passenger vehicles with displacements below 2 liters.25 SCR systems use a catalyst and an

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external source of ammonia (typically an aqueous urea solution commercially known as Diesel

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Exhaust Fluid or AdBlueTM) to reduce NOX to gaseous nitrogen and water. The (current) third

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commercial generation of SCR systems can approach 95% NOX reduction efficiency.25,26 SCR

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technology can improve fuel economy (allowing engine operation to be tuned to higher

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efficiency and higher engine-out NOX emissions, which are dealt with by the aftertreatment

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system), but it is limited by poor catalyst activity at low exhaust temperatures, especially during

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cold engine start events.25 LNT and SCR technologies dominate the Euro 6 diesel passenger car

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market (54% for LNT and 40% for SCR in 2014) in the EU, while systems combining LNT and

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SCR technology are featured in some US-market vehicles.27

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The objective of this study is to provide some insights into the relative performance of NOX

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control technologies for Euro 6 diesel passenger cars, to support both manufactures and policy

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makers in the development of technology strategies and future emission regulations. Seventy-

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three Euro 6 diesel passenger cars with three different types of NOX control technologies (8

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EGR-only, 40 LNT, and 25 SCR) were tested on a chassis dynamometer over both the NEDC

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and WLTC 2.0 hot-start driving cycles. The performance of different NOX control technologies,

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segments, and manufacturers was evaluated and discussed. Furthermore, the influence of

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different driving conditions on NOX emissions was analyzed using emission results over sub-

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cycles. Finally, the evolution of average NOX EFs for the diesel Euro 6 fleet was estimated on


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the basis of the experimental average emission factor of each manufacturer and its corresponding

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market share for the years 2012–2014.

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EXPERIMENTAL CAMPAIGN

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Test vehicles

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The chassis dynamometer tests were conducted by the ADAC (Allgemeiner Deutscher

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Automobil-Club), the largest car club in Europe, as part of its EcoTest program.28 The ADAC

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EcoTest was launched in 2003 with the aim of providing consumers with comprehensive and

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reliable information regarding the environmental performance of cars offered in Europe. This

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study includes 73 Euro 6 diesel passenger cars from 17 different manufacturers, tested from

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August 2012 to May 2015. The ADAC provided information on the NOX control technology of

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each vehicle. This vehicle sample provides a reasonable coverage of the three main NOX after-

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treatment technologies (i.e., 8 EGR-only, 40 LNT, and 25 SCR), as well as the vehicle segments

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ranging from small cars to large luxury sedans. Detailed specifications of each vehicle are given

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in the Supporting Information (Table S1).

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Emission Measurements

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The tests were conducted in the emission laboratory of ADAC Technik Zentrum in Landsberg

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am Lech, Germany. All vehicles were tested on a chassis dynamometer (Horiba Vulcan II cold)

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according to the legislative procedures for EU emissions type approval at a room temperature of

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22°C ± 2°C. A motor exhaust gas analytical system (Horiba MEXA-7000) with a constant

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volume sampler (Horiba CVS-7000) was employed to measure the regulated pollutant emissions.

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Nitrogen oxides (NOX) were measured by a chemiluminescence analyzer (Horiba CLA-750), and

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carbon monoxide (CO) and carbon dioxide (CO2) by a non-dispersive infrared (NDIR) detector


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(Horiba ALA-72X). In order to better simulate real-world conditions, some additional

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requirements were applied in addition to those of Directives (EC) 715/2007 and (EC) 692/2008:

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All vehicles were tested at their measured weight. Vehicles with a gearshift indicator were tested

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shifting the gears as indicated by the system, and daytime running lights or low-beam headlights

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were switched on for all cycles. During the WLTC hot-start test, the air conditioning system of

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the vehicles was switched on, with the temperature selector set to 20°C.29

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Driving cycles. Emissions were measured over both the NEDC (cold-start) and WLTC 2.0

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(hot-start) driving cycles. Compared with NEDC, WLTC has a higher maximum velocity (131.3

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km/h vs. 120.0 km/h), more frequent and harder accelerations, and a smaller share of idling time

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(13.0% vs. 23.7% of total cycle time) (Supporting Information, Figure S1). Thus, WLTC is

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considered to be a more realistic driving cycle that better represents actual on-road driving

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conditions.21,30

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The speed profile of WLTC version 2.0 is slightly different from the current version (5.3).

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Besides the differences in the velocity profile, there are minor differences in the gearshift model

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and in the road load settings for either model. Even though the WLTC is devised as a cold-start

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cycle, the ADAC’s EcoTest runs a hot-start version of the WLTC with a starting engine

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temperature of about 90°C. Higher NOX emissions should be expected if cold-start tests had been

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performed.

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Conformity factor. The concept of conformity factor (CF) is used to provide a simple way of

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assessing the emissions performance of a vehicle in relation to the certification limit. The CF is

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calculated as the ratio of the measured distance-specific emissions over the test cycles to a

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regulated emission limit. In this study, the reference emission limit for NOX is the type-approval

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test limit of 0.08 g/km applicable to Euro 6 diesel passenger cars. A conformity factor of 1 or


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below means that the car meets the regulatory limit, whereas a high CF is indicative of poor

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emissions performance.

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Fleet-average emission factor. The yearly fleet-average NOX EFs for Euro 6 diesel passenger

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cars were calculated via Equation (1) by taking the average NOX EFs over the WLTC 2.0 and

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NEDC of each manufacturer and weighting them by each manufacturer’s share of the EU Euro 6

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diesel passenger car market for the corresponding year (for years 2012 to 2014; see Table S2 in

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the Supporting Information).31

EFj,k = ∑ EFi,k × Pi, j 156

i

(1)

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In Equation (1), EFj,k is the estimated fleet-average NOX emission factor in year j over driving

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cycle k, g/km; EFi,k is the average NOX emission factor of manufacturer i over driving cycle

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k,g/km; and Pi,j is the share of the Euro 6 diesel passenger car market of manufacturer i in year j.

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For manufacturers with a market share smaller than 5%, or for manufacturers not represented

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in the vehicle sample, the overall average NOX EF of all other manufacturers was used. For the

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2015 projection, each manufacturer’s share of the Euro 6 market was estimated as their share of

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the total (Euro 6 and earlier) EU diesel passenger market in 2014. The underlying assumption

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here is that because every newly registered vehicle in the EU will have to comply with Euro 6 by

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September 2015, the Euro 6 diesel market share distribution will no longer be dominated by the

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few manufacturers that released their Euro 6 offerings before it was legally required. Instead, it

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will resemble the “mature” Euro 5 diesel market.

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RESULTS AND DISCUSSION NOX emissions by control technology, vehicle segment and manufacturer


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Whereas the average CO2 emissions were broadly in line for both cycles (slightly below 107%

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of type-approval values), the average NOX emissions over WLTC 2.0 were roughly five times

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the average over NEDC (Table 1), even though cold-start emissions were avoided on the WLTC

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2.0 by running the hot-start version of the cycle. To the extent that WLTC 2.0 can be considered

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as a more realistic driving cycle, the results indicate that the NEDC testing framework allows a

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large discrepancy between the actual, on-road NOX emissions and the results of the emission

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certification tests.

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Table 1. Ratios of distance-specific emissions over the WLTC 2.0 (hot-start) to the NEDC, by

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NOX control technology Emissions ratio

All vehicles (73)

NOX, WLTC / NOX, NEDC 4.9 ± 4.2 (average ± standard deviation) CO2, WLTC / CO2, NEDC 1.0 ± 0.05 (average ± standard deviation)

EGR (8)

LNT (40)

SCR (25)

2.4 ± 0.3

6.7 ± 4.8

2.7 ± 1.7

1.0 ± 0.04

1.0 ± 0.05

1.0 ± 0.06

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As Figure 1 indicates, 64 out of 73 test vehicles (88%) met the Euro 6 type-approval limit of

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0.08 g/km of NOX over the NEDC, and the remaining 12% exceeded the limit only moderately

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(between 0.001 and 0.016 g/km). In contrast, the NOX emissions performance over the WLTC

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was noticeably worse (this difference was significant according to a two-tailed paired t-test with

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α=0.01 which excluded four pairs of data points where the Z-score for the WLTC data point was

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above 2). Even without cold-start emissions, only 27% of the vehicles tested met the 0.08 g/km

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limit over the WLTC, as seen in Figure 1a.

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Most EGR-only and SCR vehicles performed better than average over the WLTC, but their

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average NOX CFs (2.1 ± 0.5 for EGR-only and 1.6 ± 1.3 for SCR) were still much higher than


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the average CF over NEDC (0.9 ± 0.1 for EGR-only and 0.6 ± 0.3 for SCR). Interestingly, LNT-

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equipped vehicles had the best average performance over NEDC (average CF of 0.5 ± 0.4), but

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also the worst over WLTC (average CF of 2.6 ± 2.9). Five vehicles equipped with LNT had very

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poor NOX emissions performances over the WLTC, with their EFs ranging from 0.55 g/km to

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1.17 g/km (CFs from 6.9 to 14.6). This is a clear indication that, in some cases, LNT technology

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is tuned in such a way that it is almost completely ineffective except when conducting the NEDC

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certification test.

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From Figure 1b it can be observed that vehicles of larger size (E and F segments; see Table S3

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for further information on market segmentation) tend to perform better, both over the NEDC and

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WLTC. This is likely due to the fact that larger cars tend to employ SCR for NOX emissions

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control because SCR systems are more economical than LNT and may provide better fuel

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economy for engines bigger than 2.0 L, and they pose fewer packaging problems in larger

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vehicles.32

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Figure 1c shows the results categorized by vehicle manufacturer. The 21 vehicles from BMW

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performed especially well over NEDC (average CF of 0.2 ± 0.1) and, despite a sixfold increase

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in average emissions over the WLTC (average CF of 1.1 ± 0.6), were still better than the overall

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average over the WLTC (CF of 2.2 ± 2.3). Nine SCR-equipped Mercedes-Benz vehicles also had

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a better than average performance over both the NEDC (CF of 0.5 ± 0.2) and WLTC (CF of 1.2

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± 0.7). One vehicle each from Volvo, Jeep, and Renault and two from Hyundai, all equipped

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with LNT, had very high NOX emissions over the WLTC (CFs of 14.6, 10.1, 8.8, 7.3 and 6.9,

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respectively). These vehicles were within or barely outside of compliance under NEDC testing

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(CFs from 0.7 to 1.1), which rules out a malfunction in the NOX control systems. They could


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therefore pass the current NEDC type-approval test, but would very likely be unfit to pass the

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future RDE test.

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Figure 1. NOX emission performance over the NEDC and WLTC 2.0 for 73 vehicles, by (a)

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NOX control technology, (b) vehicle segment and (c) manufacturer (numbers in parentheses

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indicate the number of vehicles in the subset)

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NOX emission performance by sub-cycle and technology

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The average NOX EFs of EGR-only and LNT for all phases of NEDC were below 0.08 g/km,

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the average NOX EF of SCR was slightly above the limit (0.083 g/km). However, for all sub-

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cycles of WLTC, average NOX EFs of all three technologies were significantly higher than 0.08

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g/km. LNT was the best-performing technology over NEDC, but also the worst over all phases

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of the WLTC. The standard deviations of EFs for LNT vehicles under all sub-cycles were also

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the largest among the three aftertreatment technologies studied, due to the presence of a few high

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emitters of NOX in this vehicle subset. The standard deviation of EGR-only vehicle results was

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the lowest both for NEDC and WLTC, likely due to the fact that most of the vehicles in this

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subset are from the same manufacturer (Mazda) and share the same engine.

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Figure 2a gives additional information on the relationship between the type of driving

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situations and NOX emissions for each vehicle subset. From Figure 2a, it is apparent that the

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urban phase had higher NOX emissions during the NEDC tests. Additionally, NOX emissions of

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EGR-only vehicles were similar over the urban and extra-urban phases, while LNT and

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especially SCR performed significantly worse in the urban phase. These results can be attributed

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to the influence of cold-start emissions in the urban phase of NEDC before the SCR catalyst

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light-off temperature is reached.26

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The results for the WLTC sub-cycles in Figure 2b show that high NOX emissions occur mostly

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during the extra-high-speed sub-cycle (representing highway driving). LNT vehicles had a very

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poor average performance, especially in the extra-high-speed sub-cycle, with an average CF of

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3.7 ± 4.2. This is attributed to the higher NOX emission rates overwhelming the storage capacity

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of the LNT (especially if it is only dimensioned to pass the NEDC type-approval test) and thus

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leading to NOX breakthrough in some vehicles (see right-hand side of Figure 1a). On the other


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hand, SCR-equipped vehicles performed—on average—better than EGR-only and LNT-

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equipped vehicles during the high-load, extra-high-speed sub-cycle of the WLTC, but the

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differences between SCR- and LNT-equipped vehicles were not statistically significant

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(according to Welch’s two-tailed statistical test with α=0.05) after the exclusion of five extreme

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WLTC observations with a Z-score above 2. Because the optimal temperature for SCR operation

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is around 300–400°C (higher than the normal exhaust temperature of urban driving),33 the high

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temperature of exhaust during high-load driving conditions over the extra high-speed sub-cycle

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presumably helped maintain a high NOX conversion efficiency for this vehicle subset.

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Figure 2. NOX emission factors over the NEDC phases (a) and WLTC sub-cycles (b) for 73

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vehicles, by NOX control technology (error bars indicate standard deviation)

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NOX emission performance by the WLTC sub-cycle, manufacturer and technology


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Figure 3 presents the NOX emission performance over the WLTC and its sub-cycles,

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categorized by manufacturer and NOX control technology (e.g., “Audi LNT” represents the

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subset of Audi vehicles equipped with LNT). Two BMW models equipped with SCR were the

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best performers over the WLTC, with an average EF of 0.02 ± 0.007 g/km (CF of 0.3 ± 0.09).

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LNT-equipped BMWs, SCR-equipped Mercedes-Benzes, SCR-equipped Volkswagens, and

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LNT-equipped Volkswagens had better than average EFs of 0.10 ± 0.05 g/km, 0.10 ± 0.06 g/km,

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0.10 ± 0.07 g/km and 0.11 ± 0.04 g/km respectively. The differences between the performance of

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these manufacturer-technology subsets and the average performance (not including the subset in

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question) were statistically significant according to Welch’s two-tailed statistical test excluding

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four data points with a Z-score above 2, except for the VW SCR and VW LNT subsets (likely

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due to their small size). In general, the highest NOX EFs were measured over the WLTC extra-

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high-speed sub-cycle. The five worst-performing vehicles over the WLTC (average CF of 4.5)

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were all equipped with LNTs (they are grouped in Figure 3 as “Other LNT”). This does not mean

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that LNT-equipped vehicles are unfit to pass the RDE on-road test. In fact, some of the best-

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performing vehicles over the WLTC (including 19 vehicles from BMW and two vehicles from

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Volkswagen) were equipped with LNT technology.


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Figure 3. NOX emission factors over WLTC sub-cycles for 73 vehicles, by manufacturer and

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NOX control technology (numbers in parentheses indicate number of cars in the subset)

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Trends in the fleet-average NOx emission factors of Euro 6 cars

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Figure 4 shows the estimation of fleet-average NOX EF for Euro 6 diesel cars over the WLTC

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hot-start and NEDC test from 2012 to 2014, and the projection for 2015. These were calculated

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as explained at the end of the Experimental Section. In the years 2012 and 2013, the Euro 6

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standard was not yet mandatory. As the relatively good-performing, early mover premium brands

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(e.g., BMW, Mercedes-Benz, Volkswagen) dominated the incipient Euro 6 diesel market (64%

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combined share of new Euro 6 registrations for 2012 and 66% for 2013; see Table S2),27 the

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estimated fleet average NOX EF over the WLTC 2.0 was good in relation to the Euro 6 limit

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(0.13 g/km and a CF of 1.7 for 2012 and 2013). After the Euro 6 standard became mandatory for

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all new type approvals in September 2014, other manufacturers gradually introduced their Euro 6

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diesel offerings to the market, which increased the estimated EF to 0.18 g/km in 2014 (CF of 2.2).


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Using the combined total diesel market shares of all car manufacturers in 2014 as a proxy to

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predict the Euro 6 market shares in 2015, the predicted average EF grows to 0.24 g/km (three

287

times the Euro 6 limit). By contrast, the estimated fleet-average EFs based on NEDC test results

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remain stable at 0.05 g/km (below the Euro 6 limit) for all four years. For comparison purposes,

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Figure 4 also includes the NOX EF for Euro 6 diesel vehicles as calculated from the COPERT 4

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v.10 emissions inventory model,34 using the average velocities of the WLTC sub-cycles, and

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excluding the influence of cold start. We also note that EFs resulting from on-road tests such as

292

those described by the RDE regulation—if performed on the vehicle sample of this study—

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would likely be even higher. That is because RDE tests are performed with real driving

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resistances (chassis dynamometer driving resistances used for official NEDC tests are frequently

295

unrealistically low

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variable road gradient, sudden accelerations or testing at moderate altitudes—that are known to

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increase NOX emission rates.

35

) and include elements not covered by chassis dynamometer testing—

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Figure 4. Estimated fleet-average NOX EF (NEDC and WLTC 2.0 hot) of Euro 6 diesel

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passenger cars for years 2012–2015.

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Outlook

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The NOX conformity factors over the WLTC and NEDC determined in our measurement

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campaign helped us explore the differences among the performance of different technologies, as

304

well as the differences in the robustness of the implementation of these technologies made by

305

individual manufacturers. Those results indicate that the Euro 6 limit value of 0.08 g/km is not as

306

stringent as it appears on paper, because it applies to an outdated emissions certification driving

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cycle (NEDC) that should soon be replaced by a more realistic one (WLTC).

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However, in all likelihood, the biggest challenge for diesel passenger car manufacturers will

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not arise from the certification test (be it under the NEDC or the WLTC), but from the

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impending real-driving emissions (RDE) test that is scheduled to become a mandatory step for

311

the type approval of passenger cars in the EU in 2016. Under this new testing framework, diesel

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passenger cars will have to prove they can keep NOX emissions at reasonably low levels during a

313

test that more closely represents real-world driving situations.

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In the coming months, the European Commission will work with stakeholders to determine the

315

conformity factors that will apply to on-road RDE tests. Since RDE cannot apply retroactively to

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existing Euro 6 type-approval certificates, it is essential to act fast and ensure that high emitters

317

of NOX are prevented from entering the market. The European Commission will phase in RDE

318

testing in two steps with increasing levels of stringency. It is widely expected that the initial

319

conformity factor (enforceable from September 2017 onward) will lie around a value of 2 for

320

NOX emissions from diesel passenger cars—i.e., these vehicles will still be allowed to emit about

321

twice the regulated Euro 6 emission limit of 0.08 g/km during the on-road test. Effectively, this


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makes it the first time that the Euro standards will be changed to raise an emission limit instead

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of lowering it. Moreover, because the RDE test and data evaluation procedure initially exclude

324

cold-start emissions, diesel particulate filter regenerations, aggressive driving and high-speed

325

highway driving, the real-world allowance with respect to the limit will be substantially higher

326

than indicated by the conformity factor. The second step of RDE (expected from 2019 onward)

327

should bring conformity factors close to 1, and finally include cold-start emissions. This

328

compromise should address the urgent problem of keeping Euro 6 diesel passenger cars with

329

weak on-road NOX control from being granted emissions type-approval certificates in the EU,

330

while also giving manufacturers sufficient lead time to make the necessary adjustments to

331

calibration software and emissions aftertreatment hardware to improve their vehicles’ real-world

332

NOX emissions performance.

333 334

ASSOCIATED CONTENT

335

Supporting Information

336

The time-velocity profiles of the NEDC, WLTC 2.0 and WLTC 5.3 driving cycles (Figure S1),

337

an overview of the 73 vehicles tested (Table S1), the average NOX EF of major manufacturers

338

and their market share from 2012-2015 (projection) (Table S2), and examples of vehicles in the

339

different market segments (Table S3). This material is available free of charge via the Internet at

340

http://pubs.acs.org.

341

AUTHOR INFORMATION

342

Corresponding Author

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*Phone +49.30.847.129.109; E-mail: [email protected]


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Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENT

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This work was supported by the ClimateWorks Foundation and the Stiftung Mercator. The

348

authors would like to acknowledge the Allgemeiner Deutscher Automobil-Club (ADAC) for

349

providing the experimental data.

350

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Table of Contents Graphic and Synopsis


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TOC Graphic 48x27mm (300 x 300 DPI)


Experimental Assessment of NOx Emissions from 73 Euro 6 Diesel

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