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Effects of cold temperature and ethanol content on VOC emissions from light-duty gasoline vehicles Ingrid George, Michael D. Hays, Jason Sandor Herrington, William Preston, Richard Snow, James Faircloth, Barbara Jane George, Thomas Long, and Richard Baldauf Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b04102 • Publication Date (Web): 07 Oct 2015 Downloaded from http://pubs.acs.org on October 13, 2015

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Environmental Science & Technology

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Effects of cold temperature and ethanol content on VOC emissions from light-duty gasoline vehicles

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Ingrid J. George,1 Michael D. Hays,1,* Jason S. Herrington,1,# William Preston,2 Richard Snow,1 James Faircloth,1 Barbara Jane George,3 Thomas Long1 and Richard W. Baldauf1

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6 7 8 9 10

1

Office of Research and Development, National Risk Management Research Laboratory, United States Environmental Protection Agency, Research Triangle Park, NC 27711. 2

ARCADIS U.S. Inc., Research Triangle Park, NC 27711.

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Office of Research and Development, National Health and Environmental Effects Research Laboratory, United States Environmental Protection Agency, Research Triangle Park, NC 27711.

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#

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*Corresponding Author: 109 T.W. Alexander Drive, Durham, NC 27711. Phone: (919) 5413984. Fax: (919) 685-3346. E-mail: [email protected].

14 15 16 17 18 19 20

Now at Restek Corp., Bellefonte PA 16823.

Keywords: dynamometer, gasoline exhaust, volatile organic compounds, carbonyls, mobile source air toxics, ethanol fuel

TOC/Abstract Art

Fraction of total ozone formation potential

1.0

0.8

0.6

0.4

Unsaturates

0.2

Oxygenates

Saturates BTEX 0.0

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Aromatics SE0

SE10

SE85

WE0

WE10 WE85

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1 ACS Paragon Plus Environment


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Abstract

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Emissions of speciated volatile organic compounds (VOCs), including mobile source air toxics

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(MSATs), were measured in vehicle exhaust from three light-duty spark ignition vehicles

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operating on summer and winter grade gasoline (E0) and ethanol blended (E10 and E85) fuels.

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Vehicle testing was conducted using a three-phase LA92 driving cycle in a temperature-

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controlled chassis dynamometer at two ambient temperatures (-7 °C and 24 °C). The cold start

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driving phase and cold ambient temperature increased VOC and MSAT emissions up to several

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orders of magnitude compared to emissions during other vehicle operation phases and warm

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ambient temperature testing, respectively. As a result, calculated ozone formation potentials

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(OFPs) were 7 to 21 times greater for the cold starts during cold temperature tests than

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comparable warm temperature tests. The use of E85 fuel generally led to substantial reductions

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in hydrocarbons and increases in oxygenates such as ethanol and acetaldehyde compared to E0

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and E10 fuels. However, at the same ambient temperature the VOC emissions from the E0 and

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E10 fuels and OFPs from all fuels were not significantly different. Cold temperature effects on

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cold start MSAT emissions varied by individual MSAT compound, but were consistent over a

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range of modern spark ignition vehicles.

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INTRODUCTION Ethanol is the most widely used renewable transportation biofuel in the United States.

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Consumption has increased from approximately 1% to approximately 10% of the U.S.

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transportation fuel supply in the past two decades.1 Currently, over 97% of gasoline sold in the

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U.S. contains ethanol. Most is blended at 10% by volume (also known as E10) and is used as an

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oxygenated additive. A higher ethanol/gasoline blend containing between 51 to 83% ethanol

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(commonly known as E85) by volume is available for use by flexible fuel vehicles (FFVs).

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Ethanol consumption has been encouraged by the renewable fuel standards mandated by the

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earlier U.S. Energy Policy Act (EPAct) of 2005 and more recently by the U.S. Energy

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Independence and Security Act (EISA) of 2007. Both laws were passed to improve U.S. energy

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security and independence and reduce greenhouse gas emissions from the transportation sector.2,3

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The European Union has also enacted similar legislation to promote biofuel consumption in

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Europe by setting a target of 10% energy used in the transportation sector from renewable fuels

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by 2020.4

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Vehicular emissions are a major source of atmospheric pollutants, including CO, CO2,

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particulate matter (PM), NOx and volatile organic compounds (VOCs), including a number of

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mobile source air toxics (MSATs) which are known or suspected to cause adverse health effects.

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Mobile source emissions react in the atmosphere, leading to ground-level ozone and secondary

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organic aerosol (SOA) formation, components of photochemical smog.5 The increased future

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usage of ethanol as a transportation fuel as mandated by RFS2 has generated an urgent need to

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accurately predict the ethanol fuel effects on mobile source emissions and to ensure that there is

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no further degradation in air quality due to the transition. In response, numerous recent

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dynamometer studies have characterized fuel effects on exhaust emissions of modern light-duty



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(LD) spark ignition vehicles operating on various ethanol gasoline blends.6-19 Conflicting results

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have been observed in the literature on fuel effects of ethanol addition to gasoline with respect to

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non-methane hydrocarbons (NMHC), NOx, CO, and a few MSATs (benzene and 1,3-butadiene),

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partly due to the confounding inter-study variability in fuel properties (e.g. aromatic content,

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Reid Vapor Pressure (RVP)) with ethanol blending. Differences in driving cycles, fuel blend

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preparation (i.e. splash vs. match blending) and vehicle characteristics such as the emission

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control technologies, age, models, engine calibrations of the vehicles may also help explain

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conflicting emissions data. However, there is widespread agreement that ethanol blends increase

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ethanol and acetaldehyde in exhaust emissions, with ethanol photochemically transforming to

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acetaldehyde, an important MSAT in the atmosphere. Several modeling studies have examined the health and air quality impacts of increased

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future usage of E85 blends in the U.S. and northern Europe. These studies generally suggest that

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moving to E85 may lead to small changes in ozone concentrations within a few ppb in the U.S.20-

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conditions (up to ~39 ppbv increase) compared to summertime (~7 ppbv increase) in a high NOx

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area. For wintertime driving conditions, these modeling studies either relied on extremely sparse

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emissions data of speciated VOCs and MSATs in LD vehicle exhaust (using ethanol blends or

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gasoline) at cold temperature or assumed no change in emission rates at cold temperatures.

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Notably, Ginnebaugh et al.22 predicted greater increases in ozone levels under wintertime

The objective of this study was to investigate the impact of ethanol blends (E0, E10,

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E85), ambient cold temperature (-7 vs. 24 °C) and driving cycle on speciated VOC (and MSAT)

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emissions from three LD spark ignition vehicles meeting Tier 2 emission standards. The vehicles

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were tested in a temperature controlled chamber housing a chassis dynamometer using the LA92

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driving cycle simulation. This work presents emission rates of the major ozone precursor VOCs, 4 ACS Paragon Plus Environment

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including ethanol, and MSATs in the vehicle exhaust for the three ethanol blend fuels. VOC

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MSATs investigated in this work include carbonyls (i.e., formaldehyde, acetaldehyde, acrolein),

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aromatics (i.e., benzene, toluene, ethylbenzene, xylenes (BTEX), naphthalene, styrene) and other

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toxic hydrocarbons (n-hexane, 1,3-butadiene). This research considerably improves our

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understanding of mobile source emissions of speciated VOCs, and particularly ozone precursor

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and MSAT VOCs, at cold temperatures. The improved emissions information will be used in air

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quality models to more accurately predict the health and environmental impacts of the growing

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biofuels consumption under wintertime conditions.

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EXPERIMENTAL METHODS

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Dynamometer testing

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The dynamometer testing conducted in this study has previously been described in

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detail25 and will only be covered briefly here. Dynamometer testing for this study was conducted

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at the U.S. EPA dynamometer facilities located in Research Triangle Park, NC. Three 2008

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model year light-duty Tier 2 bin 5 compliant vehicles were tested during the study: V1) Honda

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Civic LX, V2) Chevrolet Impala LS, and V3) Chrysler Town & Country. Odometer readings

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were 26,459 km for V1, 23,785 km for V2 and 78,283 for V3. Both V1 and V2 were equipped

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with multiport fuel injection systems, and V3 had a sequential fuel injection system. V2 and V3

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were flexible fuel vehicles (FFVs). Six fuels were obtained from Gage Products Co. (Ferndale,

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MI, U.S.), including summer-grade (S) and winter-grade (W) ethanol blends of E0, E10 and E85

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(henceforth designated as SE0, SE10 and SE85 for summer fuels and WE0, WE10 and WE85 for

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winter-grade fuels). The E85 blends were not tested on V1 as it was not an FFV. Fuels were

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blended to achieve seasonally-appropriate Reid vapor pressures that were consistent within

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summer and winter fuel sets. Benzene content in all fuels was kept constant at ~1% v/v. The 5 ACS Paragon Plus Environment


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ethanol volume fractions in the ethanol blended fuels are as follows: SE10 = 8.6%, WE10 =

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8.7%, SE85 = 84.0%, and WE85 = 77.7%. Fuel properties for all test fuels are listed in Table S1

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in the Supporting Information.

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Vehicle testing was conducted on a 48 in. roll electric Burke E. Porter model 4100

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chassis dynamometer (Burke E. Porter Machinery Co., Grand Rapids, MI, U.S.). The

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dynamometer was housed inside a temperature controlled test chamber, which was held at -7 or

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24 °C during vehicle preconditioning, soaking and testing with winter-grade and summer-grade

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test fuels, respectively. Vehicle testing procedures followed the Code of Federal Regulations

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(CFR), Title 40, Part 86. Emissions testing was conducted over a three-phase LA92 cycle, with

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the first 300 s representing cold start Driving Phase 1, followed by 1135 s hot stabilized Driving

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Phase 2. After a 600 s engine off segment, the entire 1435 s LA92 cycle was repeated as Driving

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Phase 3. Each set of test conditions in the study matrix (see Supporting Information Table S2)

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was tested in triplicate (or greater) on sequential test days. The vehicle preconditioning

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procedure included driving two LA92 cycles under the new test conditions and holding the

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vehicle in the climate chamber at the set ambient temperature overnight before testing. Further

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details on the fuel change procedures are found in Hays et al.25 and the Supporting Information.

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Emissions sampling and analysis

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Diluted exhaust emissions were sampled from a constant volume sampling dilution tunnel as

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described in Hays et al.25 Dilution air was preconditioned by passing through a filter and

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charcoal trap and then mixed with exhaust in the dilution tunnel at 21 °C and with a dilution

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factor between 15 to 40. A turbine (Spencer Turbine Company, Model 2025-H-SPEC, Windsor,

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CT, U.S.) was used to pull the dilution flow through the dilution tunnel, and a critical flow

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venturi (Horiba Instruments, Inc., CVS-48M, Ann Arbor, MI, U.S.) controlled the total flow rate 6 ACS Paragon Plus Environment

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of ~21 m3 min-1. Along with real-time sampling of regulated emissions with continuous

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emissions monitors, PM and VOC emissions were also sampled in a time-integrated manner

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from the dilution tunnel. While the speciated PM emissions were discussed elsewhere25, VOC

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emissions were the focus of this work. VOC measurements consisted of sampling through a 113

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°C transfer line to a pre-cleaned 6 L stainless steel canister for VOCs, a 2,4-

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Dinitrophenylhydrazine (DNPH)-coated cartridge (Sigma-Aldrich Corp., St. Louis, MO, U.S.,

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LpDNPH H30) for carbonyls, and two chilled water impingers in series for ethanol. These

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samples were integrated separately over each driving phase (Driving Phase 1, 2 and 3). A

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background sample of the dilution air was taken each test day, and one blank sample was taken

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for each set of test conditions. All sampling flow rates were controlled by calibrated mass flow

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controllers. Ethanol samples and DNPH cartridges were refrigerated until analysis. VOCs and

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ethanol samples were analyzed by gas chromatography (GC) with mass spectrometry (MS) and

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flame ionization detector (FID). DNPH cartridges were extracted with acetonitrile, and extracts

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were analyzed by high performance liquid chromatography with ultraviolet detection. Further

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details regarding analytical methods are given in the supporting information.

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Statistical analysis

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SAS 9.3 (SAS Institute Inc. 2011. SAS/ STAT 9.3 User’s Guide. Cary, NC) was used for the

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statistical analysis. Linear mixed models of emission rate concentrations were fit separately for

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each compound to assess relationships with the covariates of driving phase, temperature, and fuel

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nested within temperature (since fuels were season-specific). These models of emission rate

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concentrations used log-transformed measurements, favored by tests for normality, restricted to

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concentration measurements above the detection limit. The models accounted for the repeated

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measure structure of testing each vehicle in all three driving phases and for the fixed effect of the 7 ACS Paragon Plus Environment


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vehicle. The p-values for the tests of the differences of least square means are given in Table S7

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with the significance level set to p < 0.05.

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RESULTS

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VOC emissions by driving phase

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VOC speciation analysis of the vehicle exhaust included a total of 141 target compounds,

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of which 120 were detected in at least one diluted exhaust sample during the study. Emission

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rates for all test conditions for all individual VOCs can be found in Table S6 in the Supporting

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Information along with results from statistical testing (Table S7). Figure 1 displays average

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emissions profiles for SE0 (24 °C) tests separated by driving phase for the most highly emitted

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VOCs, which included major components of unburned gasoline fuel (e.g., 2,2,4-

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trimethylpentane, isopentane) and products of partial combustion (e.g., propylene, aromatics).

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The most abundant mobile source air toxics (MSATs), denoted with an asterisk, were benzene,

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toluene, xylenes, acetaldehyde, formaldehyde, and 1,3-butadiene. Speciated VOC emission rates

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in Driving Phase 1 cold start were at least an order of magnitude higher compared to Driving

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Phases 2 and 3 for SE0 tests, where the products of partial combustion appeared to make a

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greater contribution to total emissions in Driving Phase 1 than the unburned gasoline

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components.

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The sum of speciated VOC (ΣVOCs) emission rates (ERs) is shown by test condition and

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driving phase in Figure 2 (top panel), along with percent contributions of ethanol (middle panel)

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and sum of MSAT compounds (bottom panel) to ΣVOCs. Figure 2 clearly indicates that driving

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phase and temperature were the most important factors studied in this work impacting VOC

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exhaust emissions for all three LD vehicles studied. As noted earlier, the total VOC emissions 8 ACS Paragon Plus Environment

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were substantially higher in Driving Phase 1 cold start than Driving Phases 2 and 3 by one to

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three orders of magnitude. These differences in ΣVOCs with driving phase were statistically

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significant (p < 0.05), as they were for nearly all VOCs detected (see Table S7). ΣVOCs

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emission rates measured during the Driving Phase 1 tests at -7 °C were approximately an order

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of magnitude higher than for cold starts at 24 °C. The effect of ethanol fuel blends on ΣVOCs

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was less clear. Ethanol was the highest emitted VOC measured overall during the study.

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However, the majority of ethanol emissions (> 93%) were from Driving Phase 1 of WE85 fuel

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tests for V2 and V3, during which ethanol dominated VOC emissions (Figure 2, middle panel).

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Ethanol also made up the majority of Driving Phase 2 emissions during these two WE85 tests,

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although the emission rates were much lower than in Driving Phase 1. MSATs represented 16%

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of total VOC emissions on average as shown in Figure 2 (bottom panel). Speciated MSATs are measured less often during emissions testing than non-methane

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hydrocarbons (NMHC, as determined from total hydrocarbon and methane measurements), so it

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is generally assumed that MSAT emissions are correlated with NMHC. In this study, R2 values

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for speciated MSATs and NMHC emission rates are summarized in Table S5 in the Supporting

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Information. Although the ΣMSATs and some hydrocarbon MSATs (e.g., benzene, 1,3-

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butadiene) were strongly correlated with NMHC (R2 = 0.59 - 0.97), a weaker correlation was

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found for the carbonyl MSATs with NMHC measurements (R2 = 0.23 - 0.32). The fuel and

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temperature effects on individual VOC and MSATs emissions are discussed in more detail

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below.

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Driving Phase 1 temperature effects VOC emissions increased dramatically during Driving Phase 1 from 24 °C to -7 °C tests,

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which was consistently observed for all three vehicles and for all fuels (Figure 2). Statistically

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significant increases of at least a factor of two for the majority of the individual VOCs,

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ΣMSATs, ΣVOCs and NMHC with the decrease in test cell temperature were observed (see

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Table S7). However, there were a few notable exceptions, where changes of less than a factor of

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two were found for acetone, acrolein, n-butane, and formaldehyde for E0 and E10 tests.

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Formaldehyde emissions decreased with the cold temperature for both E0 and E10, consistent

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with the more fuel rich combustion conditions needed during colder temperature/cold start

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operation. Comparisons of VOC emission profiles for 24 °C and -7 °C tests for a given vehicle

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and ethanol blend indicated that the VOC emission profiles changed to some extent (R2 ~ 0.63 –

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0.92) with test cell temperature.

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This change can be seen more clearly in Figure 3, displaying the relative changes in VOC

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emissions for each individual VOC grouped by compound class and averaged for each ethanol

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blend. As a reference, NMHC emissions increased in Driving Phase 1 on average by 9 - 10 times

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for all fuels, while ΣVOCs increased by ~7, 9 and 23 times for E0, E10 and E85 fuels,

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respectively. Aromatics (ARs) aside from BTEX (i.e. benzene, toluene, ethylbenzene, xylenes)

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and unsaturated (UNSAT) compounds had the greatest range of relative changes, with the

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highest relative increases up to a few hundred times, particularly for E85 tests. Relative changes

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with temperature for BTEX, saturated compounds (SATs) and oxygenates were up to ~40 times

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for Driving Phase 1. The smallest changes in emissions were observed for oxygenates, but the

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temperature effect was more pronounced during E85 tests for these compounds.


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These results are consistent with emissions of both unburned fuel components and

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products of partial combustion for both gasoline and ethanol rising due to the fuel rich

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combustion conditions needed during cold temperature cold start operations, but the degree of

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the effect may vary by individual VOC and the fuel used. It is probable that the combustion

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conditions may need to be even more fuel rich with E85 use during cold temperature cold starts

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than with the lower ethanol blends due to the higher heat of vaporization of E85. This could

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explain the intensified temperature effects on the emissions with increasing ethanol content in

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the fuels as seen in Figure 3. Engine calibration, an important factor that influences exhaust

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emissions at cold start, was not studied in depth in this work.13

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Driving Phase 1 fuel effects

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The impact of E10 and E85 compared to E0 fuel blends are shown as average relative changes in

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individual VOC emissions by compound class and temperature in Figure 4. Whereas cold

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temperature effects generally led to significant increases in most VOCs (Figure 3), the

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directionality, magnitude, and degree of statistical significance of the changes in VOC emissions

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due to use of ethanol-blended fuels was highly dependent on whether or not the VOCs originated

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from the fuel components. Most compounds did not show significant changes in emissions from

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E0 to E10 for either summer or winter blends (Table S7). However, emissions of many

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hydrocarbons were significantly impacted when E0 and E10 blends were compared to E85 under

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the same temperature. The emissions of compounds that were most strongly linearly related to

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ethanol emissions generally increased with use of ethanol blend fuels, particularly for E85

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blends, including acetaldehyde, acetylene and other carbonyls (Oxygenates) and C2

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hydrocarbons. In addition, the emissions of the majority of the VOCs associated with the



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petroleum fuel component and its combustion byproducts decreased consistently as the

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petroleum fuel fraction decreased.

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Because the change in the ambient temperature from 24 to -7 °C led to an increase in

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VOC emissions generally, the reductions in gasoline related VOC emissions due to the ethanol

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blend fuel effect were partially counteracted at cold temperatures. For example, Driving Phase 1

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benzene emissions changed from an ~ 30% reduction for SE85 to an ~ 40% increase for WE85

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compared to respective E0 blends. Note that the changes in benzene emissions corresponded to

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much higher p-values (p = 0.01 - 0.44) as seen in Table S7 for the E85 blend fuel comparisons

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compared to the other monoaromatic compounds (p < 0.0001), likely due to the fixed benzene

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content (~ 1%) in all fuels. Therefore, the benzene emissions were less reflective of changes in

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BTEX in this study, but may indirectly indicate the increase in fuel consumption and/or fuel

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enrichment during combustion. While non-methane hydrocarbon emissions generally decreased

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from E0 to other ethanol blends (statistically significantly for fuel comparisons with E85 blends),

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ΣMSATs and ΣVOCs increased for some tests using E85 at 24 °C and both E10 and E85 fuels at

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-7 °C, mainly due to dramatic increases in acetaldehyde and ethanol.

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Ozone formation potentials

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The VOC emission rates determined from this study were weighted by their relative

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ozone reactivities and summed for each test condition to determine total ozone formation

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potentials (ΣOFPs) in units of g O3/km based on the Maximum Incremental Reactivity (MIR)

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scale as outlined by Carter.26 The MIR scale is used to determine the maximum potential impact

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of an incremental increase in VOC mass emissions on ground level ozone formation, typically

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assuming relatively high NOx conditions (i.e., VOC-limited conditions for ozone formation). It


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should be noted this paper does not address NOx impacts and that real-world air quality impacts

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will depend on ratios of hydrocarbons to NOx. Best-estimate MIR values (in g O3/g VOC) used

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convert emission rates to OFPs for all tests are listed in Table S6 for all individual VOCs. The

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relative contribution of each VOC compound class to the ΣOFPs during Driving Phase 1 for each

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fuel averaged over the test vehicles is summarized for each test fuel in Figure 5 along with ΣOFP

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values. OFP values are given for each test condition and statistical results are in the Supporting

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Information (Table S6 and S7, respectively). Driving Phase 2 and 3 ΣOFPs were only a few

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percent of the Driving Phase 1 values, so the focus of this discussion is on Driving Phase 1 only.

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The general trends in ΣOFPs for each temperature were E10 < E0 < E85. However, the

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fuel effects on ΣOFPs were not statistically significant (see Table S7). Unsaturated compounds

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(particularly ethylene, propylene and isobutene/1-butene) were responsible for the majority of

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the ozone reactivity for E0 and E10 blends, whereas oxygenates (mostly ethanol and

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acetaldehyde) contributed the most to the OFPs for E85 blends. Cold ambient temperature led to

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statistically significant increases in OFPs between 7 to 21 times for the three ethanol blends. The

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highest ΣOFP value was calculated for WE85 emissions at 18.1 g O3/km. The influence of

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ethanol fuel and cold temperature on relative contributions of compound classes and changes in

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OFP values in this study are in agreement with previous dynamometer studies.7, 11, 27 However,

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the OFP values in this work are substantially higher for both ambient temperatures when

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compared with Driving Phase 1 values from other studies despite excluding CO in our

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calculation, possibly due to the more extensive VOC speciation of both hydrocarbons and

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oxygenates included in the calculations here, or the difference in absolute emissions for different

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driving cycles and vehicles.



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DISCUSSION

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Comparison with literature

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From this work, it is clear that cold ambient temperature has considerable impact on VOC

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emissions during cold starts for light-duty vehicles operating on gasoline/ethanol blended fuels.

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This research suggests that the magnitude of the cold temperature effects on MSATs is highly

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dependent on the fuel composition (see Figure 3). To determine whether this trend is generally

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robust and to gain a better understanding of the current state of the research, cold temperature-

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induced changes in MSAT emissions at cold starts from the literature were compared with this

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work as summarized in Figure 6. Seven studies were included that measured and reported MSAT

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emission changes from “warm” (20 to 24 °C) to “cold” (-7 to -10 °C) temperatures for light-duty

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vehicles of model year ≥ 1998 with three-way catalysts (mostly Tier 2, Euro4 and 5a emission

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standards) operating on a range of ethanol blends from E0 to E85.7, 9, 11, 27-30 This study is the first

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of its kind to our knowledge to report cold temperature cold start changes for all twelve MSATs

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listed in Figure 6 for Tier 2 or similar vehicles, where half the MSATs have no previously

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reported cold temperature ERs. As shown in Figure 6, the pattern of cold temperature increases

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by ethanol blend for individual MSATs in the literature are remarkably consistent with this work

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apart from the large variations in the literature values for benzene in the range of -0.4 to +174

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times (full scale version of Figure 6 shown in the Supporting Information). In fact, average

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values by fuel from this study and the literature were linearly related (slope = 1.1, R2 = 0.88)

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when compared pairwise if benzene values were excluded, suggesting that the relative trends in

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cold temperature effects on MSATs (apart from benzene) by ethanol-blended fuel from this

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study may be relevant to other spark ignition vehicles of similar model years.


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SPECIATE is a U.S. EPA speciated VOC and PM emission profile database for

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numerous emission sources used to create emission inventories and used in source receptor and

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air quality models. Emission profiles from this work have been added to SPECIATE Version

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4.431 (profiles #8904 - 8927). VOC emission profiles from this work brought a substantial

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increase in the number of E85 profiles in the SPECIATE database including the first cold

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temperature E85 profile. The emission profiles from this work were compared to 250

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gasoline/ethanol blend exhaust speciated VOC profiles. The relative contribution of MSATs to

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the emission profiles from other SPECIATE profiles are shown with those from this work in the

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Supporting Information (Figure S2). Although generally comparable trends in MSAT %

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contributions are observed between this work and previous emission profiles, the values from

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previous studies span several orders of magnitude for each MSAT due to a number of inter-study

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differences that may impact VOC emissions.

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Air quality implications of cold temperature effects

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In this study, driving tests for LD vehicles using E0, E10 and E85 simulating wintertime

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ambient conditions (-7 °C) led to dramatic increases in cold start MSAT emissions (Figure 6)

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and ozone formation potentials (Figure 5) by nearly an order of magnitude greater than emissions

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during standard testing conditions (24 °C). As noted earlier, air quality modeling studies have

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suggested that the overall impact of increased E85 use on ground-level ozone formation is on a

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much smaller scale, which appears to be highly dependent on NOx emission changes and less

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sensitive to VOC emission changes than assumed by the OFP calculation.20-24 Another reason for

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the minimal predicted effects of E85 use is that the increase in oxygenated ozone precursor

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emissions with E85 use are counterbalanced by a reduction in hydrocarbon ozone precursors.



332

Nevertheless, this study suggests that the ozone formation potential of E85 emissions should

333

increase at colder temperatures, which these air quality studies have not yet taken into account.

334

Another factor that moderates the environmental impact of E85 in air quality models is that

Page 16 of 27

335

direct acetaldehyde emissions from mobile sources contribute a small fraction to overall ambient

336

acetaldehyde levels, especially in summer due to relatively greater photochemical acetaldehyde

337

production.32 In winter, direct acetaldehyde emissions become more important in urban areas

338

compared to summer, but ozone production is less important in wintertime generally due to

339

reduced photochemical activity. Thus, on a regional scale, the fuel effect of E85 on ground-level

340

ozone production may lead to negligible modifications to ozone levels. Near road emissions of

341

MSATs such as acetaldehyde may be important, particularly at colder temperatures where

342

increased MSAT emissions and less photochemically produced acetaldehyde are expected.

343

An ongoing source of uncertainty in modeling the air quality and health impacts of mobile

344

sources is the temperature dependence of mobile source emissions and the lack of up to date

345

speciated emissions data for modern vehicles at cold temperatures.33 This study and our previous

346

work on emissions of heavy-duty trucks using biodiesel blends34 have attempted to fill some

347

gaps to better understand cold temperature effects of exhaust emissions, particularly MSATs and

348

VOCs, from modern vehicles operating on biofuels. However, newer Tier 2 vehicles that are

349

required to be compliant with the 2007 MSAT Rule35 are expected to have lower MSAT

350

emissions at cold temperatures than the MY 2008 test vehicles studied in this work. We have

351

only performed testing at two temperatures, so the mathematical relationship between emissions

352

and temperature cannot be ascertained. A few studies have measured emissions at multiple

353

temperatures,28, 36, 37 and have found that VOC/MSAT emissions increase nonlinearly (in some

354

cases exponentially) with decreasing temperature during cold starts. Clearly, more studies are 16 ACS Paragon Plus Environment

Page 17 of 27


355

needed to understand how emissions are influenced by ambient conditions, which is essential to

356

accurate assessment of the environmental impacts of the transportation sector.

357

ACKNOWLEDGMENTS Authors would like to thank Eastern Research Group, Inc. for analytical support, and

358 359

Joseph McDonald, Rich Cook and Deborah Luecken from U.S. EPA for helpful discussions. The

360

views expressed in this article are those of the authors and do not necessarily represent the views

361

or policies of the U.S. Environmental Protection Agency.

362

Supporting Information

363

A description of VOC analysis details is included in the supporting information along

364

with tables of fuel properties, fuel change procedures, test matrix, linear comparisons of VOCs,

365

VOC emission rates, and table of statistical results. Figures include a full scale version of Figure

366

6 and a comparison of data with SPECIATE and literature values. Note that Tables S6 and S7 are

367

presented in a separate Microsoft Excel file as tabbed sheets. This information is available free of

368

charge at http//pubs.acs.org/.

369

References

370

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(2) Energy policy act of 2005. Public Law 109-58, 2005;

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2015).

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http://www.gpo.gov/fdsys/pkg/BILLS-110hr6enr/pdf/BILLS-110hr6enr.pdf (accessed May

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2015).



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temperatures of +22 °C and -7 °C; Final Report; Swedish Road Administration: Stockholm,

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653.

477 478 479 480 481 482



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483 484 485

Figure 1. Average emission profiles by driving phase for all vehicles for SE0. Error bars

486

represent 1 standard deviation of mean values. Mobile source air toxics are labeled with an

487

asterisk.

488


Page 23 of 27


V1

% Ethanol

ΣVOCs ER (g/km)

Temp.= 10

24

V2 -7

24

V3 -7

24

-7

1

0.1

0.01

100 80 60 40 20

% MSATs

0 100 80 60

Driving Phase 1 Driving Phase 2 Driving Phase 3

40

489

V1 V1 -SE -S 0 V1 E1 0 V 1 -W E -W 0 E V2 10 S V2 E -S 0 V2 E1 -S 0 V2 E8 5 V 2 -W E -W 0 V2 E -W 1 0 E V3 85 V3 -SE -S 0 V3 E1 -S 0 V3 E8 5 V 3 -W E -W 0 V3 E -W 1 0 E8 5

20

490 491

Figure 2. Average sum of VOCs (ΣVOCs, top panel) emission rates (ER), ethanol (middle

492

panel) and mobile source air toxics (MSATs, bottom panel) fraction (in %) of ΣVOCs for all test

493

conditions by driving phase. Error bars represent 1 standard deviation of mean values.

494



Page 24 of 27

(ER-7C - ER24C) / ER24C

100 E0 E10 E85

80

300

200

100

60 0 AR

BTEX

UNSAT

SAT Oxygenates

40

20

0

495

AR

BTEX

UNSAT

SAT

Oxygenates

496

Figure 3. Relative changes in individual VOC emissions in Driving Phase 1 from 24 to -7 °C

497

averaged by fuel and grouped by compound class: aromatics except BTEX (AR), BTEX,

498

unsaturated (UNSAT) and saturated (SAT) hydrocarbons, and oxygenates (Oxygenates). Inset

499

shows full scale.

500

501

502

503


Page 25 of 27


(ERE10,E85 - ERE0) / ERE0

5

SE10 WE10 SE85 WE85

4 3 2 1 0 -1

504

AR

BTEX

UNSAT

SAT

Oxygenates

505

Figure 4. Relative changes in individual VOC emissions in Driving Phase 1 from E0 averaged

506

by temperature and fuel and grouped by compound class: aromatics except BTEX (AR), BTEX,

507

unsaturated (UNSAT) and saturated (SAT) hydrocarbons, and oxygenates (Oxygenates) . Four

508

points are off scale for Oxygenates (SE85= 33.1, 44.3; WE85= 8.2, 94.0).

509

510

511



Relative contribution of each VOC compound class to total OFP

ΣOFP (g O3/km) = 1.0

0.91

0.71

1.1

7.9

7.7

Page 26 of 27

18.1

0.8

UNSAT SAT Oxygenates BTEX AR

0.6

0.4

0.2

0.0 SE0

SE10

SE85

WE0

WE10

WE85

512 513

Figure 5. Relative contribution of each compound class (unsaturated (UNSAT) and saturated

514

(SAT) hydrocarbons, oxygenates (Oxygenates), aromatics except BTEX (AR) and BTEX)) to

515

Phase 1 total ozone formation potentials (ΣOFP) for each fuel. Average ΣOFP values are listed

516

above the respective columns.

517

518

519

520

521


Page 27 of 27


(ERcold - ERwarm) / ERwarm

60 This work - E0 This work - E10 This work - E85 Lit. - E0-E5 Lit. - E10-20 Lit. - E75-85

50 40 30 20 10

1,

3-

522

n-

Bu

ta

di

en e H e Fo xa rm ne al de hy Ac de et al de hy de Ac ro le in Be n ze Et hy ne lb en ze ne To lu en m e ,p -X yl en e oXy le N ne ap ht ha le ne St yr en e M SA Ts

0

523

Figure 6. Relative changes in cold start mobile source air toxic (MSAT) emissions at cold

524

temperature for this work and the literature7, 9, 11, 27-30. Several data points for benzene and

525

naphthalene are off scale with a full scale version shown in the Supporting Information (Figure

526

S1).


Effects of Cold Temperature and Ethanol Content ... - ACS Publications

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