Experimental Assessment of NOx Emissions from 73 Euro 6 Diesel

Nov 18, 2015 - School of Environment, State Key Joint Laboratory of Environment ... Seventy-three Euro 6 diesel passenger cars (8 EGR only, 40 LNT, an...
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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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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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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

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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

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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

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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

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

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

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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

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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

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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

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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

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

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

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

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

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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

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

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

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

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

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

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

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

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

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NOX emissions performance.

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ASSOCIATED CONTENT

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Supporting Information

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

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

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

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

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http://pubs.acs.org.

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AUTHOR INFORMATION

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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

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

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providing the experimental data.

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Table of Contents Graphic and Synopsis

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