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Total Particle Number Emissions from Modern Diesel, Natural Gas, and Hybrid Heavy-Duty Vehicles During On-Road Operation Tianyang Wang, David Christopher Quiros, Arvind Thiruvengadam, Saroj Pradhan, Shaohua Hu, Tao Huai, Eon S Lee, and Yifang Zhu Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 22 May 2017 Downloaded from http://pubs.acs.org on May 24, 2017

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Environmental Science & Technology

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Total Particle Number Emissions from Modern Diesel, Natural Gas,

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and Hybrid Heavy-Duty Vehicles During On-Road Operation

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Tianyang Wang1, 2, David C. Quiros3, Arvind Thiruvengadam4, Saroj

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Pradhan4, Shaohua Hu3, Tao Huai 2,3, Eon S. Lee2, and Yifang Zhu1, 2*

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1. Institute of the Environment and Sustainability, University of California, Los Angeles, California, 90095, United States

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2. Department of Environmental Health Sciences, Jonathan and Karin Fielding

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School of Public Health, University of California, Los Angeles, California, 90095,

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United States

12 13 14 15

3. Monitoring & Laboratory Division, California Air Resources Board, Sacramento, California, 95814, United States 4. Mechanical and Aerospace Department, West Virginia University Morgantown, West Virginia 26506, United States.

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Submit to Environmental Science and Technology for Publication

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*Corresponding Author: Yifang Zhu: [email protected]; Phone: (310) 825-4324; Fax:

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(310) 794-2106; 650 Charles E. Young Drive South, 51-295B CHS, Los Angeles, CA

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90095;

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ACS Paragon Plus Environment


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Abstract Particle

emissions

from

heavy-duty

vehicles

(HDVs)

have

significant

23

environmental and public health impacts. This study measured total particle number

24

emission factors (PNEFs) from six newly-certified HDVs powered by diesel and

25

compressed natural gas totaling over 6,800 miles of on-road operation in California.

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Distance-, fuel- and work-based PNEFs were calculated for each vehicle. Distance-

27

based PNEFs of vehicles equipped with original equipment manufacturer (OEM) diesel

28

particulate filters (DPFs) in this study have decreased by 355-3200 times compared to a

29

previous retrofit DPF dynamometer study. Fuel-based PNEFs were consistent with

30

previous studies measuring plume exhaust in the ambient air. Meanwhile, on-road

31

PNEF shows route and technology dependence. For vehicles with OEM DPFs and

32

Selective Catalytic Reduction Systems, PNEFs under highway driving (i.e., 3.34 ×1012 to

33

2.29 ×1013 particles/mile) were larger than those measured on urban and drayage

34

routes (i.e., 5.06 ×1011 to 1.31×1013 particles/mile). This is likely because a significant

35

amount of nucleation mode volatile particles were formed when the DPF outlet

36

temperature reached a critical value, usually over 310 °C, which was commonly

37

achieved when vehicle speed sustained over 45 mph. A model year 2013 diesel HDV

38

produced approximately 10 times higher PNEFs during DPF active regeneration events

39

than non-active regeneration.

40

41

42


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43


TOC Art

44



45

1. Introduction

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Exhaust from on-road heavy-duty vehicles (HDVs) have been identified as a

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major sources of air pollution1–4. Diesel HDVs emit substantial amounts of oxides of

48

nitrogen (NOx) and particulate matter (PM). Recognizing the air quality and public

49

health impacts of diesel HDVs emissions, the California Air Resources Board (CARB)

50

and the U.S. Environmental Protection Agency (EPA) have adopted stringent

51

certification standards for PM and NOx. Beginning with model year (MY) 2007 and MY

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2010 engines, the limits regulated by CARB are 0.01 g PM/bhp-hr and 0.2 g NOx/bhp-

53

hr. CARB also adopted the Truck and Bus Regulation in 2008, which requires phase-

54

out of older equipment and the adoption of MY 2010 or newer technology in several

55

regions of the state by 20235. Consequently, advanced aftertreatment technologies,

56

such as diesel oxidation catalysts (DOC), diesel particle filters (DPF), and selective

57

catalytic reduction (SCR) systems, have been widely used in on-road diesel HDVs6.

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These aftertreatment systems may reduce NOx and PM emissions by more than 90%,

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and under certain conditions by up to 99%3,7. The PM exhaust from DPF-equipped

60

HDVs contains a large amount of nucleation mode particles ( 250 °C).

395

Figure 5 shows that the median PNEFs during active regeneration (i.e., 2.97

396

×1012 and 3.54×1013 particles/mile for events 1 and 2, respectively) were 13 and 195

397

times higher than without regeneration, 8 and 179 times higher than passive

398

regeneration, respectively (Mann-Whitney-Wilcoxon test p-values both < 0.001). These

399

trends suggest that active regeneration could substantially increase total PNEFs,



400

especially if a vehicle operates predominately at low speeds and relatively low particle

401

number emission levels (event 2). The PNEF during active regeneration event 1 was

402

lower than during event 2 (Mann-Whitney-Wilcoxon test p-values < 0.001). This

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indicates that at a higher vehicle speed where total PNEF is likely dominated by volatile

404

particles, there would be less dramatic increases in total PNEF during a brief active

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regeneration.

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It is important to note that these emissions were measured from in-use rental

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trucks that have exceeded their de-greening period by a few thousand miles, but do not

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represent the vast majority of trucks operating on highways that travel significantly

409

beyond their regulatory useful life of 435,000 miles for heavy-HD on-road diesel

410

engines. After several hundred thousand miles, emission control system deterioration

411

may occur, which could change the frequency, magnitude, and other characteristics of

412

PM emissions during DPF regeneration events.

413

estimated 8% of diesel HDVs operating within California that ARB staff concluded had

414

appreciably damaged DPFs7,25. The total and solid particle number emissions from

415

these vehicles with damaged aftertreatment systems, and their relationships to PM

416

mass emissions, to our knowledge, has yet to be rigorously quantified.

As of May 2015, there were an


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Figure 5. The boxplots of real-time PNEFs of Vehicle 5 during two active regeneration events, compared with their corresponding passive regeneration and no regeneration status at the same vehicle speed range and route classification. TAT is DPF aftertreatment temperature. The lower and upper hinges of the box are 25th and 75th percentile, respectively; lower whisker is the smallest observation ≥ (lower hinge - 1.5 × IQR); upper whisker is the largest observation ≤ (upper hinge + 1.5 × IQR); the black horizontal line is the median.

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426

Supporting Information

427 428 429 430 431 432

Table for the standard deviations of particle number emission factors by vehicle and technology group; figures for testing route, instrumentation of the transportation emission measurement system, PNEF correlation between CPC_CVS and CPC_Ejector, trip-specific average PNEFs and DPF temperature differences in Vehicle 4, the impact of DPF temperatures (intake and outlet) on PNEF, and PNEF distributions of additional tests in Vehicle 4.


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