# Effe cts of Gasoline Sulfur Lev el on Emissions fr om the Tier 2 In - Use Fleet

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## Ar on Butler

, Da vid Choi, K en t Helmer , To nyF ernandez, P aul Machiele (USEP A/OTA Q/ ASD) CRC Real W orld April 10, 2013

## • Ve hicle emissions ha ve long been known to e xhibit “NOx cr eep” due t o sulfur in the fuel • Re cen t ga soline sulfur pr ogr ams

– Look ed at effect shortly after a “cleanout cycle”

– Didn’t attempt to assess impact on emissions fr om in - use fleet 

## • This s tudy assesses sensitivity of in - use Tier 2 v ehicles t o fuel sulfur lev el

– What is the level of r eversible cat alyst activity loss in the in - use fleet?

– Do emission benefits of lower sulfur (<10 ppm) continue with mileage accumulation?

– What level of over all emission r eduction is expect ed fr om the in - use fleet?



# Back **ground & Objective** 

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## • Re cruit ed 81 vehicles fr om owner s

– MY 2007 - 2009 passenger cars and light trucks with 20,000 to 40,000 odomet er miles

– Ta rgeted five vehicles each fr om make/model/engine “classes” select ed for EP Act pr ogr am to be r epr esent ative of national sales in 2007 - 8 timefr ame



# Design Over**vie w**  **- Ve**  **hicles**

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## Vehicle **Mak e**  **Veh icle**  **Model** FOR D 500, E xplor er, F150, Fo cu s HON DA Ci vi c, Od ys sey NI SSA N Al ti ma DODG E Cal ibe r, Caravan TOYOTA Corol la, Sie nna, Tac om a CHEVR OLE T Cobal t, Im pala, Silv era do JE EP Libe rt y SATURN Outlook

## • Tw o non - ethanol tes t fuels

– Pur chased bulk deliv ery of typical “ Tier 2 cert fuel” with 5 ppm sulfur

– Segr eg ated and adjusted a portion up to 28 ppm



# Design Over**vie w**  **- Fu**  **els**

**Fuel Pr operty**  **ASTM Method Low S T**  **est Fuel** Sulfur D2622 5 ppm To tal Ar omatics D5769 31.2 Vo l % Olefins D1319 0.5 Vol % T50 D86 221 ° F T90 D86 317 ° F RVP D5191 9.0 psi

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## • 3 - bag FTP cy cle at 75 ° F • Measur ed g aseous pollutants and PM mass by bag • High - speed/load “clean - out ” consisting of two back - to - back US06 cy cles

• Fo cus on thr ee r esear ch ques tions:

– What is “clean - out effect ” with 28 ppm t es t fuel? • Is sulfur loading on the catalyst reversible? How do emissions from recruited vehicles differ before/after a clean - out cycle?

– What is “clean - out effect ” with 5 ppm t es t fuel? • Ar e emissions immediately following the clean - out cycle different at different sulfur levels?

– What is the effect of sulfur level with mileage accumulation?



# Design Over**vie w**  **- Procedures** 

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### Assess effect of r ever sible sulfur loading in the catalys t immediately after ve hicle arriv es (all 81 v ehicles)



# Procedures: **Clean -**  **out Ef**  **fe ct at 28**  **ppm**

6Assess change in emissions as a function of sulfur level over mileage accumulation Subset of one sample of each make/model performed additional series of repeated emission tests covering up to 180 miles on each sulfur level Alternated FTP tests with on road mileage accumulation on routes with speeds and loads similar to FTP

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# Procedures: **Sulfur Le vel**  **Ef fe**  **ct**After mid - term review of available data, the short procedure was extended to include additional tests on low- sulfur fuel to provide information about an immediate sulfur level effect (23 vehicles including data from this and previous slide)

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# Procedures: **Clean -**  **out Ef**  **fe ct at 5 ppm** 

# Analysis **Approach**
• Data analyz ed by bag of the FTP (cold start, hot running)

• Log tr ans fo rma tion of emission measur emen ts

– St abiliz e v ariance, obtain linearity between dependent variable and fix ed and r andom effects, normaliz e distribution of r esidual



## • Analyz ed using linear mix ed model

– Mor e r obust and flexible in modeling the covariance structure for “r epeat ed measur es dat a”

– Capable of including vehicles with missing dat a and handling irr egularly spaced measur ements

– Bette r accounts for within - vehicle mileage dependent int er actions

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# Analysis **Approach**

• Used top - down model fit ting str ate gy

– St art with a satur ated model with all candidat e fix ed effects

– Select a model with most optimal covariance structure

– Re duce the fix ed effects portion of the model to fit the final model


## • Once the final model was fit, the differ ence of leas t squar es means between the fix ed effects of in te re stwe re re ve rs e tr ans fo rmed to estimate the per cen t r eduction in emissions
• Analysis of the effect of sulfur lev el on bag 2 NO x 

## pr esen te d in gr ea te r detail for illus tr ative purposes

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**NO x**  **(p -** **value) THC** 

**(p -** **value) CO** 

**(p -** **value) NMHC** 

**(p -** **value) CH**  **4**

**(p -** **value) PM** 

**(p -** **value) Bag 1** 

– – 4.7% (0.0737) – – 15.4% (< 0.0001) **Bag 2** 31.9%

(0.0009) 16.5%

(0.0024) – 17.8% (0.0181) 15.3%

(0.0015) – **Bag 3** 38.3%

(<0.0001) 21.4%

(<0.0001) 19.5%

(0.001 1) 27.8%

(<0.0001) 12.0%

(<0.0001) 24.5%

(<0.0001) **FTP Wtd**  11 .4%

(<0.0001) 4.1%

(0.0187) 7.6%

(0.0008) 3.0%

(0.0751) 6.9%

(0.0003) 13.7%

(<0.0001) The effect is not significant at α = 0.10 when no reduction estimate is provided .



# “Clean **- Out**  **Ef**

**fe ct**  **” at 28ppm** 17 ve hicle families; 81 unique v ehicles Number of measur ements: n = 479 (242 pr e / 237 pos t) **Pe rc**  **ent reduction f or FTP**  **set immedia tely after “** **clean -**  **out ”**  **vs. bef** **or e** 12 **NO x**  **(p -** **value) THC** 

**(p -** **value) CO** 

**(p -** **value) NMHC** 

**(p -** **value) CH**  **4**

**(p -** **value) PM**  **Bag 1** 10.7%

(0.0033) 8.5% †

(0.0382) 7.5% †

(0.0552) 7.5%

(< 0.0001) 13.9% †

(< 0.0001) – **Bag 2** 59.2%

(< 0.0001) 48.8%

(< 0.0001) – 44.8% † (0.0260) 49.9%

(< 0.0001) – **Bag 3** 62.1%

(< 0.0001) 40.2%

(< 0.0001) 20.1%

(< 0.0001) 49.9%

(< 0.0001) 29.2%

(< 0.0001) – **FTP Wtd**  23.0% †

(0.0180) 13.0% †

(0.0027) 11 .9% †

(0.0378) 10.6% †

(0.0032) 25.8% †

(< 0.0001) – † Model with significant sulfur and mileage interaction term. W here no reduction estimate is provided, the ef

fect is not significant at α = 0.10. 

# Overall **Emission R eduction for 5 vs. 28ppm**  17 ve hicle families; 23 unique v ehicles Number of measur ements: n = 228 (114 at 5ppm / 114 at 28ppm) **Pe rc**  **ent reduction a t 5 vs. 28 ppm a**  **t all mileag e levels** 13

**NO x**  **(p -** **value) THC** 

**(p -** **value) CO** 

**(p -** **value) NMHC** 

**(p -** **value) CH**  **4**

**(p -** **value) PM**  **Bag 1** 5.9%

(0.0896) 5.4%

(0.01 18) 7.3%

(0.0023) 4.6%

(0.0465) 11 .1%

(<0.0001) – **Bag 2** 47.3%

(0.0010) 40.2%

(<0.0001) – 34.4% (0.0041) 53.6%

(<0.0001) – **Bag 3** 51.2%

(<0.0001) 35.0%

(<0.0001) 10.1%

(0.0988) 45.0%

(<0.0001) 25.4%

(<0.0001) – **FTP Wtd**  17.7%

(0.0001) 11 .2%

(<0.0001) 8.3%

(0.0003) 8.8%

(0.0003) 21.4%

(<0.0001) – The ef fect is not significant at α = 0.10 when no reduction estimate is provided.



# Sulfur E **ff ect on “Clean**  **- Out**  **”** 17 ve hicle families; 23 unique v ehicles Number of measur ements: n = 132 (64 at 5ppm / 68 at 28ppm) **Pe rc**  **ent reduction a t 5 vs. 28ppm**  **fo r tests**  **<50 miles after cleanout**

# NOx **Bag 2: Dat a vs. Predicted** 

14 Comparison of actual data (blue) to model prediction (red) for several vehicles15

R - square = 0.72 

# NOx **Bag 2: Dat a vs. Predicted**  Showing high and low sulfur data points compared to model prediction

# Sensitivity **Analyses**
• Fo cused on bag 2 NOx

– Low emission r ates, large percent reductions



## • Ex amined effects of

– Re moving vehicles with very low emission levels (sample < 100 ppb, about half of observations)

– Re moving t es ts with z er o emission r esults vs. imputing small values (half the minimum valid r esult, affecting about 8% of observations)

– Re moving influential vehicles (r es tricted likelihood distance > 1.5, thr ee vehicles)



### • In each c ase, **model pr edictions**  **remained statistically**  **significan t**  and within a r ang e of 51 - 70% reduction (vs. baseline at 59%), sugg esting r obustness of results 16

# Summary **Conclusions**

• Catalyst efficiency loss due to sulfur loading is occurring in the Tier 2 in use fleet

– Measur eable effect on emissions of NO x and other pollut ants of int er es t

– Aft er performing a clean - out cycle on 28 ppm fuel, dat a shows FTP composit e NO x wa s r educed by 11% and NMHC by 3%



### • Ef fe ctiv eness of high speed/load modes in r es toring catalyst efficiency are limited by fuel sulfur lev el

– Comparing t es ts on 5 vs. 28 ppm fuel immediat ely aft er a “clean - out ” cycle: FTP composit e NO x emissions wer e 18% lower , NMHC 9% lower

, and CO 8% lower

– Suggests the initial clean - out r esults wer e limit ed by 28 ppm sulfur fuel

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### • Re ducing fuel sulfur lev els fr om 28 to 5 ppm is e xpected to bring significant r eductions in NO x

### , NMHC, and other pollutants of interest in the in - use fleet

– Contr olling for sulfur effects by mileage wher e appr opriate: FTP composit e NO x wa s 23% lower

, NMHC w as 11% lower

, and CO 12% lower

– Emission performance on lower sulfur fuel did not converge with higher sulfur as miles wer e accumulat ed, but inst ead showed a const ant (or incr easing) ra tio



### • The ov er all findings of significant emission benefits of ≤10 ppm sulfur in Tier 2 v ehicles ar e in agr eement with other r ecent s tudies by EP A and aut omobile and catalyst manufactur er s 1,2,3

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# Summary **Conclusions**19

References 1. Chapter 6 of the Regulatory Impact Analysis for the Control of Hazardous Air Pollutants from Mobile Sources Final Rule, EPA 420 - R - 07 - 002. 2. Ball D., Clark D., Moser D. (2011). Effects of Fuel Sulfur on FTP NOx Emissions from a PZEV 4 Cylinder Application. SAE 2011 W orld Congress Paper 2011 - 01 - 0300. SAE International: Wa rrendale, PA. 3. Shapiro, E. (2009). National Clean Gasoline, An Investigation of Costs and Benefits. Published by the Alliance of Automobile Manufacturers, Wa shington, DC. 

# Fu**rther R eading**  The s tudy r eport and data will be ava ilable

via the OTA Q w ebsite: htt p://www .epa.gov/otaq/fuelsmodel.htm