Well-to-Wheels Emissions Analysis of BMW 3-Series - Gas vs. Diesel





Introduction



This analysis quantifies the well-to-wheels (WTW) emissions of the gasoline and diesel versions of the 2018 model year BMW 3-Series based on the latest EPA emission factors.


Methodology


Here, two otherwise identical vehicles are examined - the 2018 BMW 328d (diesel) certified as LEV2 "ultra-low emission vehicle" (ULEV II) by CARB, and the 2018 BMW gasoline 330i (specifically, the 330i model certified as LEV3 SULEV30 by CARB, which means that it is equivalent to the PZEV classification. PZEV classification means that the vehicle is certified to California's strictest emission classification (super-ultra-low emission vehicle - SULEV), plus be certified to have evaporative emissions below a "diminimus" value considered by CARB to be zero). The PZEV version of the gasoline 330i receives a "smog rating" of "9" by the EPA (on a scale of 1-10), while the ULEV version of the Passat TDI receives a "smog rating" of "6" (https://www.epa.gov/greenvehicles/smog-rating). In the California rating system (http://www.driveclean.ca.gov/Know_the_Rating/Understand_the_Smog_Rating.php), the PZEV 330i also receives a "smog rating" of "9", while the ULEV 328d receives a "smog rating" of "6".

The official CARB certification data sheets are available at https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2018/bmw_pc_a0080444_2d0_s3-30.pdf (gasoline 330i PZEV) and https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2018/bmw_pc_a0080465_2d0_u2_diesel.pdf (328d (diesel)).

EPA emission factors were used to estimate "upstream" emissions of criteria pollutants, i.e., emissions produced in the "well-to-pump" (WTP) phase of the life-cycle emissions. The U.S. EPA published emissions factors for WTP emissions for gasoline and diesel fuel in a support document to the recently-issued "Proposed Rulemaking for 2017-2025 Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards" (EPA, "Draft Joint Technical Support Document: Proposed Rulemaking for 2017-2025 Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards." http://www.epa.gov/otaq/climate/documents/420d11901.pdf (Table 4-12, page 4-42 [366 of 479])). The following is a reproduction of Table 4-12...





Since the WTP emissions are a function of fuel consumption, the emission factors were divided by 1,000,000 (emissions per 1,000,000 BTUs), multiplied by the lower heating value (LHV) energy in BTUs per gallon (129,488 BTU/gallon for ULS diesel fuel; 116,090 BTU/gallon for conventional gasoline), and divided by the fuel mileage. For example...


Conventional Gasoline upstream VOC emissions...

3.035 grams (Petroleum Extraction & Transportation) + 3.162 grams (Total Petroleum Refining) + 42.91 grams (Fuel Transport, Storage, Distribution) = 49.107 grams VOC/mmBTU

49.107 grams/mmBTU / 1,000,000 BTU = 0.000049107 grams/BTU

0.000049107 grams/BTU X 116,090 BTU/gallon = 5.7 grams VOC/gallon

5.7 grams VOC/gallon / 27.3913 miles/gallon (unrounded combined mileage of 330i) = 0.208 grams/mile in the well-to-pump phase


Low Sulfur Diesel upstream VOC emissions...

3.035 grams (Petroleum Extraction & Transportation) + 3.063 grams (Total Petroleum Refining) + 1.261 grams (Fuel Transport, Storage, Distribution) = 7.359 grams VOC/mmBTU

7.359 grams/mmBTU / 1,000,000 BTU = 0.000007359 grams/BTU

0.000007359 grams/BTU X 129,488 BTU/gallon = 0.95 grams VOC/gallon

0.95 grams VOC/gallon / 35.6864 miles/gallon (unrounded combined mileage of 328d) = 0.027 grams/mile in the well-to-pump phase...


Emissions from the vehicles themselves ("pump-to-wheels" (PTW)) were based on the California Air Resources Board (CARB) certified emissions.

The 3-day and SFTP 2-day diurnal evaporative emissions from the gas vehicle were averaged and were converted from grams per test to grams per mile by dividing grams/test value by 57.5 based on the following data...

Average U.S. temp = 52.85 degrees F (https://www.ncdc.noaa.gov/cag/)

True VP = 3.444 psi @ 50 F; 4.2188 psi @ 60 F = (4.2188 - 3.444) = 0.7748 / 10 = 0.07748 X (52.85 - 50 = 2.85) = 0.22 + 3.444 = 3.66 psi @ 52.85 F (interpolated)

Average temp of SHED (2/3-day diurnal test) = 84 F (http://www.ecfr.gov/)

True VP @ 84 F = 6.1891 psi @ 80 F; 7.4184 psi @ 90 F = 6.68 psi @ 84 F

3.66/6.68 = 0.5479 [adjustment factor]

Average US car VMT = 11,493 miles/year (http://www.epa.gov/cleanenergy/energy-resources/refs.html)

11,493 mi/year / 365 days/year = 31.5 mi/day / 0.5479 = 57.5


Fuel economy values (for calculation of ORVR and VOC emissions ancillary to the operation of the vehicles, and for WTP emissions) were obtained from the unrounded combined mileage in the 2018 EPA Fuel Economy Datafile available at http://www.fueleconomy.gov/feg/download.shtml.

Cold CO and NMOG emissions of the gasoline vehicle were not considered.

The "composite" emissions are a weighted average of emissions over the FTP/US06/SC03 test duty cycles. The weighting is 35%:28%:37%, FTP75:US06:SC03, respectively, as defined in the EPA document, "Draft Regulatory Impact Analysis: Tier 3 Motor Vehicle Emission and Fuel Standards." http://www.epa.gov/otaq/documents/tier3/420d13002.pdf, page 1-16.

ORVR conversion...
Gasoline - grams/gallon / fuel mileage (miles/gallon).



Results


Certified exhaust emissions per CARB certification data ("Composite" = combined FTP/US06/SC03 emissions weighted at 35%/28%/37%, respectively)...


2018 LEV2 ULEV 328d

NMOG (FTP75 @ UL) = 0.015 g/mi
CO (FTP75 @ UL) = 0.2 g/mi
NOx (FTP75 @ UL) = 0.01 g/mi
PM (FTP75 @ UL) = 0.0002 g/mi
NMOG+NOx (Highway @ UL) = 0.0004 g/mi
CO (Composite @ UL) = 0.07 g/mi
NMOG+NOx (Composite @ UL) = 0.018 g/mi

2018 LEV3 SULEV30 330i

NMOG+NOx (FTP75 @ UL) = 0.012 g/mi
CO (FTP75 @ UL) = 0.2 g/mi
PM (FTP75 @ UL) = 0.001 g/mi
NMOG+NOx (Highway @ UL) = 0.006 g/mi
CO (Composite @ UL) = 0.4 g/mi
NMOG+NOx (Composite @ UL) = 0.014 g/mi

Incorporating WTP emissions per EPA emission factors...


2018 328d (35.6864 mpg (from unrounded EPA value))

(Grams/Mile)


EmissionWTPPTWWTW Total 
 
NMOG/VOC+NOx0.1510.0180.169
CO0.0420.070.112
PM0.0130.005**0.018
SOx0.0650.002***0.067
 


2018 330i SULEV30 (27.3913 mpg (from unrounded EPA value))

(Grams/Mile)


EmissionWTPPTWWTW Total 
 
NMOG/VOC+NOx0.3620.026*0.388
CO0.0520.40.452
PM0.0170.006**0.023
SOx0.0800.002***0.082
 

(@ WTW composite emissions per EPA Emission Factors (combined FTP/US06/SC03))

(Grams/Mile)


Emission2018 328d2018 330i 
 
NMOG+NOx0.1690.388
CO0.1120.452
PM0.0180.023
SOx0.0670.082
 


*Includes evap emissions from vehicle - ~=0.014 g/mi @ FTP and SC03; 0.008 g/mi @ US06

**Includes PM emissions generated from brake and tire wear per GREET1_2017

***PTW SOx emissions per GREET1_2017

All PM assumed to be PM2.5


[HC = NMOG/VOC for purposes of the chart]



Conclusion


As can be seen, "clean diesel" vehicles are generally no "worse" with respect to total well-to-wheels emissions than the cleanest gasoline vehicles due to the nature of the very low volatility of diesel fuel and overall lower emissions in the WTP phase, even though the BMW 328d is "only" certified T3B125/ULEV II, while the BMW 330i gasoline version is certified the equivalent of PZEV. In fact, based on these EPA emission factors, the 328d has lower WTW criteria pollutant emissions across-the-board than the PZEV version of the gasoline 330i.




Argonne National Laboratory released the latest version of the GREET model (GREET1_2017) in October 2017. GREET1_2017 is available on the ANL GREET web page (http://greet.es.anl.gov/).

Using GREET1_2017 to estimate upstream criteria pollutants, and using the same methodology as described above, with the exception that a 43% city/57% highway drive cycle mix is used (consistent with what EPA uses in its MOVES modeling), the following are the WTW emission results of the 3-Series BMWs. [Note - upstream (WTP) emissions include well drilling and well infrastructure]



Results


Certified exhaust emissions per CARB certs ("Composite" = combined FTP/US06/SC03 emissions weighted at 35%/28%/37%, respectively)...


2018 LEV2 ULEV 328d

NMOG (FTP75 @ UL) = 0.015 g/mi
CO (FTP75 @ UL) = 0.2 g/mi
NOx (FTP75 @ UL) = 0.01 g/mi
PM (FTP75 @ UL) = 0.0002 g/mi
NMOG+NOx (Highway @ UL) = 0.0004 g/mi
CO (Composite @ UL) = 0.07 g/mi
NMOG+NOx (Composite @ UL) = 0.018 g/mi

2018 LEV3 SULEV30 330i

NMOG+NOx (FTP75 @ UL) = 0.012 g/mi
CO (FTP75 @ UL) = 0.2 g/mi
PM (FTP75 @ UL) = 0.001 g/mi
NMOG+NOx (Highway @ UL) = 0.006 g/mi
CO (Composite @ UL) = 0.4 g/mi
NMOG+NOx (Composite @ UL) = 0.014 g/mi

Incorporating WTP emissions per GREET1_2017...


2018 328d (33.25 miles per gallon gasoline equivalent (mpgge) @ 43%/57%)

(Grams/Mile)


EmissionWTPPTWWTW Total 
 
NMOG/VOC+NOx0.1440.0180.162
CO0.0740.070.144
PM0.0080.010**0.018
SOx0.0720.002***0.074
 


2018 330i SULEV30 (28.613 mpgge @ 43%/57%)

(Grams/Mile)


EmissionWTPPTWWTW Total 
 
NMOG/VOC+NOx0.2820.026*0.308
CO0.1210.40.521
PM0.0120.009**0.021
SOx0.1130.002***0.115
 



(@ WTW emissions per GREET1_2017 (combined FTP/US06/SC03))

(Grams/Mile)


Emission2018 328d2018 330i 
 
NMOG+NOx0.1620.308
CO0.1440.521
PM0.0180.021
SOx0.0720.115
 

*Includes evap emissions from vehicle - ~=0.014 g/mi @ FTP and SC03; 0.008 g/mi @ US06

**Includes PM emissions generated from brake and tire wear; GREET1_2017 default exhaust PM emissions used

***PTW SOx emissions per GREET1_2017

All PM assumed to be PM2.5



[HC = NMOG/VOC for purposes of the chart]



Of course, the 328d also has the traditional benefits of a diesel...

(@ WTW emissions per GREET1_2017)

(BTU/mile or Grams/Mile)


Attribute2018 328d2018 330i 
 
Total Energy41385097
Petroleum Energy35703986
GHG Emissions340390
 


Conclusion


Regardless of the source of the emission factors (EPA or GREET1_2017), the BMW 328d has lower WTW criteria pollutant emissions across-the-board than the SULEV30-certified gasoline 330i.




One argument made is that "upstream" (i.e., well-to-pump) emissions occur primarily in rural areas and thus do not expose a large portion of the population to those emissions. The GREET model estimates upstream (WTP) urban emissions along with total emissions. The following are the urban emissions calulated by GREET1_2017. Used FTP emission results for pump-to-wheels (PTW) emissions.


2018 328d

(Grams/Mile)


EmissionWTPPTWWTW Total 
 
NMOG/VOC+NOx0.0270.0250.052
CO0.0080.20.208
PM2.50.0010.0036**0.0046
SOx0.0170.001***0.018
 


2018 330i SULEV30

(Grams/Mile)


EmissionWTPPTWWTW Total 
 
NMOG/VOC+NOx0.0900.026*0.116
CO0.0130.20.213
PM2.50.0030.0045**0.0075
SOx0.0250.001***0.026
 



(@ WTW emissions per GREET1_2017 (combined FTP/US06/SC03))

(Grams/Mile)


Emission2018 328d2018 330i 
 
NMOG+NOx0.0520.116
CO0.2080.213
PM0.00460.0075
SOx0.0180.026
 


*Includes evap emissions from vehicle - ~=0.014 g/mi @ FTP and SC03; 0.008 g/mi @ US06

**Includes PM emissions generated from brake and tire wear

***PTW SOx emissions per GREET1_2017

All PM assumed to be PM2.5



[HC = NMOG/VOC for purposes of the chart]



Thus, the 328d still has as low or lower WTW emissions across-the-board in urban areas than the cleanest gasoline 330i available.




Taking this analysis a step further, EPA has published "damage costs" of regulated pollutants it uses to estimate societal cost benefits to reductions in pollutants expected from specific regulations. The damage costs in this section are based on a recent EPA "Regulatory Impact Analysis" technical document.


Methodology


Marginal Damages (per EPA - "Draft Regulatory Impact Analysis: Proposed Rulemaking for 2017-2025 Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards"; Table 7.1-6.4-1, page 7-2, available here).


Damage costs per EPA...

NMOG/VOC - $1,300/ton
NOx - $5,500/ton (vehicle use)
NOx - $5,300/ton (fuel production and distribution and vehicle manufacturing)
PM2.5 - $300,000/ton (vehicle use)
PM2.5 - $250,000/ton (fuel production and distribution and vehicle manufacturing)
SOx - $32,000/ton

Conversion from dollars/ton to cents/gram - dollars/ton X 1 ton/2000 pounds X 1 pound/453.6 grams X 100 cents/dollar = cents/gram

NMOG/VOC - 0.143 cents/gram
NOx - 0.606 cents/gram (vehicle use)
NOx - 0.584 cents/gram (fuel production and distribution & vehicle manufacturing)
PM2.5 - 33.069 cents/gram(vehicle use)
PM2.5 - 27.557 cents/gram (fuel production and distribution & vehicle manufacturing)
SOx - 3.527 cents/gram


Since the NMOG and NOx certified emissions are combined in some driving cycles (e.g., US06), the same methodology that ACEEE uses in its damage cost analysis is used here for the gasoline vehicle (i.e., the gasoline vehicles' NMOG+NOx emissions are assumed to be 67% NMOG and 33% NOx (http://greenercars.org/sites/default/files/2016methodologyupdate.pdf, "Tier 3 Methodology", page 4)). Based on EPA's measured NMOG and NOx emissions in its in-use emissions testing, the NMOG+NOx emissions are assumed to be 14% NMOG and 86% NOx for the 328d.

The output files from GREET1_2017 are broken down by "Feedstock" (e.g., emissions produced during extraction of oil and its transportation to the refinery); "Fuel" (Refining of the oil and its transportation to the pump).
From GREET2_2017 - "Vehicle" (All emissions associated with production of the vehicle).
"Operation" involves emissions produced from operation of the vehicles (e.g., exhaust emissions).

Thus, the GREET output for the respective emissions in grams/mile are multiplied by the EPA damage costs in cents/gram which gives cents/mile (vehicle mile traveled).

The GREET output results are adjusted according to the official EPA mileage ratings for each vehicle relative to the fuel mileage assumed in GREET1, and the weight of the respective vehicles relative to the weight assumed in GREET2


For the BMW 3-Series vehicles...

2018 328d curb weight (per BMW) - 3510 lbm = 3510/3183 (weight assumed in GREET2) = 1.1027
2018 330i curb weight (per BMW)  - 3541 lbm = 3541/3183 = 1.112

2018 328d fuel mileage (per EPA) - 33.25 mpgge = 31.3 mpg (diesel mileage (gasoline equivalent) assumed in GREET1)/33.249 = 0.9414
2018 330i fuel mileage (per EPA)  - 28.613 mpg = 29.992 mpg (SIDI gasoline mileage assumed in GREET1)/28.613 mpg = 1.0482


Results


328d - 0.3475 ("Operation") + 0.3487 ("Feedstock") + 0.1849 ("Fuel") + 0.8126 ("Vehicle Manufacturing") = 1.6937 cents/vehicle mile traveled (VMT)
330i  - 0.3106 ("Operation") + 0.3208 ("Feedstock") + 0.4839 ("Fuel") + 0.8198 ("Vehicle Manufacturing") = 1.9351 cents/vehicle mile traveled (VMT)


Graphical representation of these results...



Thus, the diesel version of the BMW 3-Series (328d) produces significantly less full life-cycle damage to public health and the environment than the PZEV-certified gasoline version (330i), per data from GREET and EPA.