Air Resourc,es Board 

Mary D. Nichols, Chairman 

9480 Telstar Avenue, Suite 4 

Matthew Rodriquez 

Secretary for 

Environmental Protection 

El Monte, California 91731 • www.arb.ca.gov Edmund G. Brown Jr. 

December 29, 2014 

Mr. Matthew Spears 

Center Director 

U.S. Environmental Protection Agency 

2000 Traverwood Drive 

Ann Arbor, Michigan 48105 

Dear Mr. Spears: 

Governor 

I am writing to request that the U.S. Environmental Protection Agency (U.S. EPA) 

require a mandatory supplemental check for oxides of nitrogen (NOx) emissions for 

hybrid vehicles in the Phase 2 Greenhouse Gas (GHG) Standards, scheduled for 

proposal next spring. This letter outlines the reasons why the Air Resources Board 

(ARB) is concerned. about possible excess NOx emissions from hybrid vehicles and 

how we propose preventing such excess emissions. 

ARB estimates that an additional 90 percent reduction in the NOx emission standard is 

needed from heavy duty diesel engines in order to attain federal ambient air quality 

standards in the South Coast and San Joaquin air basins in 2032. 1 Hence, California 

needs to ensure that the Phase 2 standards not only do not result in increased N~ 

emissions, but position us to collaboratively pursue lower NOx standards once the 

Phase 2 standards are finalized. This is especially important as we expect additional 

non-attainment areas nationwide will also be pressed to achieve more NOx reductions 

once the new, more stringent federal ozone standard is promulgated. 

Background 

ARB strongly supports the development and deployment of heavy-duty hybrid vehicles 

and sees heavy-duty hybrid technology as a key stepping stone toward meeting 

California's air quality and climate goals. In fact, through California's Hybrid and ZeroEmission Truck and Bus Voucher Incentive Project, ARB has provided funding for 

nearly 1 ,500 heavy-duty hybrid vehicles over the past four years. In addition to hybrid 

technologies' potential fuel economy improvements and air quality benefits, ARB staff 

1 ARB and the South Coast Air Quality Management District are working to refine the estimate of 

emission reductions needed as part of the 8-hour ozone plan due to U.S. EPA in 2016. 

The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. 

For a list of simple ways you can reduce demand and cut your energy costs, see our website: http://www.arb,ca.gov. 

California Environmental Protection Agency 

Printed on Recycled Paper 
Mr. Matthew Spears 

December 29, 2014 

Page 2 

expects hybrids to play a substantial role in further advancing the development of 

battery and electric drive components that are needed for heavy-duty near-zero and 

zero-emission vehicles. As discussed below, in order to achieve their full emission 

reduction potential, it is necessary for the hybrid system to be fully integrated with the 

vehicle's engine and emissions after-treatment systems. 

Heavy-duty hybrid vehicles with greater than 14,000 pounds gross vehicle weight rating 

are required to be equipped with a certified engine and onboard diagnostic systems that 

monitor both the engine and hybrid systems and notify the operator if an issue exists 

with the emission control system. While the engine is the only part of the system 

currently tested for emission compliance under certification, it is obvious that the 

hybridization of the vehicle which manipulates the performance of the engine can lead 

to emission profile changes. 

Hybrid technologies for heavy-duty diesel vehicles have been demonstrated to reduce 

fuel consumption when compared to conventional diesel vehicles. In addition, if the 

hybrid system is well designed and integrated, NOx emissions from a hybrid vehicle can 

also be lower compared to a comparable conventional vehicle. However, if the hybrid 

system was insufficiently integrated to the vehicle's engine and emissions aftertreatment systems, hybrid vehicles can have significantly higher NOx emissions 

compared to conventional vehicles2

. 

To ensure the NOx performance of heavy-duty hybrid vehicles and better support their 

development and deployment, ARB developed voluntary certification procedures, 

"California Interim Certification Procedures for 2004 and Subsequent Model Hybl'{dEiectric and Other Hybrid Vehicles in the Urban Bus and Heavy-Duty Vehicle Classes", 

which were adopted in 2002 and amended in 2013. ARB's voluntary certification 

procedures were designed for heavy-duty hybrid vehicle manufacturers seeking 

voluntary vehicle-based certification using a chassis dynamometer. The voluntary 

procedures provide for the determination of a NOx certification value for a hybrid vehicle 

using a ratio method of chassis dynamometer test results of the hybrid vehicle and a 

comparable conventional baseline vehicle. The certification value for a heavy-duty 

hybrid vehicle is determined through calculations using chassis dynamometer test 

results and engine certification values for both the hybrid vehicle and a comparable 

conventional vehicle. Chassis testing is done using two default duty cycles, including 

the Orange County Bus Cycle and the Heavy-Duty Urban Dynamometer Driving 

Schedule (UDDS), one of which can be replaced with another test cycle that the 

certifying party believes to be more representative of the specific vocational duty cycle 

that the hybrid vehicle will see. 

2 Data Collection, Testing, and Analysis of Hybrid Electric Trucks and Buses Operating in California 

Fleets, Final Draft, May 2014 
Mr. Matthew Spears 

December 29, 2014 

Page 3 

Recommendations 

To address the potential NOx emission increases for heavy-duty hybrid vehicles 

discussed above, we recommend a mandatory supplemental check for NOx emissions 

for all hybrid vehicles used to meet the Phase 2 standards. Hybrid vehicles should be 

required to confirm compliance to current NOx emission standards using the 

supplemental check, as illustrated in the Attachment. 

We recommend using the ratio method included in ARB's "California Interim 

Certification Procedures for 2004 and Subsequent Model Hybrid-Electric and Other 

Hybrid Vehicles in the Urban Bus and Heavy-Duty Vehicle Classes." ARB's certification 

procedures specifically require the use of chassis dynamometer testing. To allow 

additional flexibility, ARB staff recommends allowing powertrain testing, as described in 

40 Code of Federal Regulations 1037 as an option to chassis dynamometer testing. 

We recommend that the Orange County Bus Cycle or UDDS cycle be used, along with 

another test cycle that the certifying party believes to be more representative of the 

specific vocational duty cycle of the hybrid vehicle.3 

We recognize that requiring the recommended supplemental check will add cost to 

hybrid manufacturers. In 2013, staff surveyed three vehicle chassis test laboratories 

and estimated that the total testing costs is approximately $30,000 per test vehicle or 

hybrid engine family, excluding test vehicle pick-up and delivery service. Some hybrid 

manufacturers may have difficulties accessing chassis or powertrain test time for their 

vehicles due to the limited availability of test facilities. ARB's research and discussions 

with stakeholders found 11 chassis dynamometer and 5 powertrain test cell sites~n 

North America. Most of the test sites are for research and in-house use only. 

We are recommending two possible approaches to address testing cost and 

accessibility issues mentioned above: 

• Do not make the supplemental check mandatory if vehicle manufacturers 

can demonstrate compliance with the Phase 2 carbon dioxide fleet average 

(g/ton-mile) without counting the contribution from their hybrid vehicles. 

This would remove the possibility of Phase 2 standards incentivizing 

manufacturers to build hybrids that ultimately increase NOx. For manufacturers 

not counting hybrid vehicles toward the Phase 2 fleet averages, in lieu of the 

supplemental check, U.S. EPA could require submittal of emission test data 

3 A hybrid vehicle manufacturer that is planning to measure hybrid vehicle C02 using the ARB transient 

test cycle on a powertrain test could satisfy the requirement for a supplemental NOx check by measuring 

NOx during the ARB transient test, powertrain testing their hybrid vehicle for NOxon either the UDDS or 

Orange County bus cycle, and then powertrain testing a conventional diesel vehicle for NOx on both test 

cycles for A to B comparison purposes. 
Mr. Matthew Spears 

December 29, 2014 

Page4 

-~------

indicating NOx emissions are acceptable via another method, for example from 

Portable Emission Measurement Systems (PEMS) testing; or 

• Require a supplemental check confirming compliance to current NOx · 

standards only for high-volume manufacturers of hybrids. U.S. EPA could 

require the supplemental check only for manufacturers with projected or actual 

combined national sales of heavy-duty hybrid vehicles of some de minimis 

amount, for example, 500 units per year. For lower-volume manufacturers of 

hybrids, in lieu of the supplemental check, U.S. EPA could require submittal of 

emission test data indicating NOx emissions are acceptable via another method, 

for example from PEMS testing. 

ARB staff believes that including this supplemental cheQk for NOx emissions in Phase 2 

rule is an important element in avoiding NOx increases for heavy-duty hybrid vehicles. 

This procedure would provide manufacturers flexibility and a more straightforward 

mechanism to certify hybrid vehicles. It would also encourage manufacturers to further 

deveiop advanced technologies. 

If you have questions or need additional information, please contact Ms. Kim HeroyRogalski, Manager, at (916) 327-2200, or email at kheroyro@arb.ca.gov or me at (626) 

575-6632, or email at mcarter@arb.ca.gov. 

Sincerely, .) (\ . '/ / ( 

(}+-~ _;; . dl>c~ jb1, CtL Le~ tr' 

.~~ v~fl/J!lAJ~~J 

Michae Carter, Chief 

Mobile Source Regulatory Development Branch 

California Air Resources Board 

Attachment 

cc: James Tamm 

Fuel Economy Division Chief 

National Highway Traffic Safety Administration 

Annette Hebert, Division Chief 

Emissions Compliance, Automotive Regulations and Science Division 

Kim Heroy-Rogalski, Manager 

Strategic Planning & Development Section 

\ 
Mr. Matthew Spears 

December 29, 2014 

Attachment 

Example of Certification by Emission Factor Ratio Application 

Example 1 - For example, manufacturer XYZ produces heavy-duty hybridelectric buses and performs chassis dynamometer testing with the following data: 

Hybrid-electric Bus NOx = 0.51 g/mi (chassis dynamometer) 

Engine (Hybrid-electric Bus) NOx = 0.17 g/bhp-hr (engine certification level) 

Baseline Diesel Bus NOx = 0.95 g/mi (chassis dynamometer) 

Engine (Baseline Diesel Bus) NOx = 0.19 g/bhp-hr (engine certification level) 

EF (Emission Factor) = Vehicle NOx (g/mi) 

Engine NOx (g/bhp-hr 

EFhybrid = 0.51 g/mi = 3.0 bhp-hr/mi 

0.17 g/bhp-hr 

EFbaseline =0.95 g/mi = 5.0 bhp-hr/mi 

0.19 g/bhp-hr 

EFR (Emission Factor Ratio) =EFhybrid 

EFbaseline 

EFR = 3.0 bhp-hr/mi =0.60 

5.0 bhp-hr/mi 

Hybrid-Electric NOx cert = EFR * Engine NOx 

Hybrid-Electric NOx cert = 0.60*0.17g/bhp-hr =0.1 0 g/bhp-hr < 0.2 g/bhp-hr 

certification standard \ 

Manufacturer XYZ's hybrid bus would pass the supplemental check. 

Example 2 - For example, manufacturer ABC produces heavy-duty hybridelectric buses and performs chassis dynamometer testing with the following data: 

Hybrid-electric Bus NOx = 1.53 g/mi (chassis dynamometer) 

Engine (Hybrid-electric Bus) NOx = 0.17 g/bhp-hr (engine certification level) 

Baseline Diesel Bus NOx = 0.95 g/mi (chassis dynamometer) 

Engine (Baseline Diesel Bus) NOx = 0.19 g/bhp-hr (engine certification level) 

EF (Emission Factor) = Vehicle NOx (g/mi) 

Engine NOx (g/bhp-hr 

EFhybrid = 1.53 g/mi = 9.0 bhp-hr/mi 

0.17 g/bhp-hr 
Mr. Matthew Spears 

December 29, 2014 

Attachment 

EFbaseline =0.95 g/mi = 5.0 bhp-hr/mi 

0.19 g/bhp-hr 

EFR (Emission Factor Ratio) =EFhybrid 

EFbaseline 

EFR = 9.0 bhp-hr/mi =1.80 

5.0 bhp-hr/mi 

Hybrid-Electric NOx cert = EFR * Engine NOx 

Hybrid-Electric NOx cert = 1.80*0.17g/bhp-hr =0.31 g/bhp-hr > 0.2 g/bhp-hr 

certification standard 

Manufacturer ABC's hybrid bus would not pass the supplemental check. 

\