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Supporting Technical Document

March 1, 2013

MEMORANDUM

SUBJECT: Estimated Reductions in Particulate Matter Emissions from Light-duty and Medium-duty 

Gasoline Vehicles through Implementation of Tier 3 Regulations.

FROM: Darrell Sonntag – USEPA/OTAQ/ASD

TO: EPA Docket # EPA-HQ-OAR-2011-0135

Overview

The NPRM Tier 3 RIA estimated reductions in particulate matter (PM) emissions from light-duty vehicles.

The estimated PM reductions were modeled through reductions in particle-phase organic carbon (OC) 

which was projected to be reduced by 30% through improvements in controlling lubricating oil 

consumption. Similar reductions were projected for medium-duty gasoline engines that are regulated 

under Tier 3 standards. No reductions in particulate matter emissions were projected for light-duty 

diesel engines. The technical analysis underlying the 30% OC reduction assumption was based on an 

analysis of data collected from the Kansas City Light-Duty Vehicle Emissions Study (KCVES). 

Lubricating Oil Contribution to PM Emissions using the Kansas City Light-Duty Emissions Study

Sonntag et al. (2012) estimated the contribution of lubricating oil to light-duty PM emissions using data 

from the KCVES1. A brief description of the analysis is provided in this technical document. In 2005, the 

US Environmental Protection Agency (EPA) completed a vehicle emission sampling campaign in the 

Kansas City Metropolitan Statistical Area (KCMSA) to improve understanding of the contribution of lightduty gasoline vehicles to ambient particulate matter (PM). The KCVES recruited 496 light-duty vehicles 

in a stratified random sample from the KCMSA. The KCVES tested each vehicle on a chassis 

dynamometer using the California Unified Cycle. The chemical composition of the PM emissions was 

chemically analyzed from a subset of 99 vehicles. Measurements of particle-phase organic species were 

measured from 52 individual and composite PM samples obtained from these 99 vehicles.

The contribution of lubricating oil to the elemental carbon (EC), organic carbon (OC), total carbon (TC), 

and total particulate matter (PM) emissions was estimated using hopanes and steranes as markers for 

the lubricating oil, with three polycyclic aromatic hydrocarbons used as gasoline markers. A fleetweighted regression model was used to apportion particulate emissions to lubricating oil and gasoline, 

according to the population of the Kansas City vehicle fleet.

The vehicle samples from pre-1991 model years were analyzed separately from 1991-2004 model year 

vehicles. The older vehicles contribute disproportionately to the fleet-average PM emissions derived 

from lubrication oil. While only contributing 13.5% of the vehicle population, the pre-1991 vehicles 

contribute 70% of the oil-derived PM for the entire fleet, and 33% of the fuel-derived PM. Lubricating oil 
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is a significant contributor to organic carbon emissions, with older vehicles emitting a large percentage 

of OC emissions from the lubricating oil. Lubricating oil was estimated to contribute 60% of the OC 

emissions from the pre-1991 vehicles, and only 21% of the OC for the 1991-2004 vehicles. The greater 

contribution of lubricating oil in the older vehicles is expected due to deterioration and malfunction of 

older vehicles. Elemental carbon emissions were dominated by the gasoline contribution, with no 

detectable contribution from lubricating oil. Fleet-average PM emission rates were calculated from 

weighting the contribution of each set of model year vehicles to their estimated population in the 

KCMSA. Based on this weighting, the contribution of lubricating oil emissions to PM was estimated to be 

25%, which was roughly half the contribution of fuel to PM (47%).

A complete apportionment of the EC, OC, TC, and PM between fuel and lubricating oil was not possible 

due to varied chemical composition of PM among vehicles, uncertainties in the fuel and oil marker 

measurements, metals and dust in the exhaust, and PM measurement artifact. The uncertainty was

estimated by applying a survey data analysis re-sampling method to the regression estimates. 95% 

confidence intervals for the lubricating oil contribution to the fleet-average PM emissions range from 

13% to 37%. More information regarding the data, analysis steps and model assumptions, used to reach 

these conclusions are documented in Sonntag et al. (2012)1.

Estimated Reduction in PM emissions by Tier 3 standards

The Tier 2 PM emission standard is 10 mg/mi on the FTP cycle. MOVES2010 estimates that the average 

PM emissions from 2005 and later light-duty gasoline vehicles are well in compliance with the Tier 2 

standards. Using MOVES2010 light-duty PM emission rates to simulate an FTP cycle, the FTP composite 

emissions for passenger cars and trucks are estimated as 2.72 mg/mi and 3.08 mg/mi, respectively when 

the vehicles are between 0-3 years old. MOVES2010 predicts that 2005 model year vehicles will 

eventually exceed the Tier 2 standards when the vehicles are aged to 20 years. MOVES2010 assumes 

that PM emission rates for 2006 and later model year vehicles begin at the same levels as PM emissions 

from new 2005 vehicles, and deteriorate at same rate as they age. 

The proposed Tier 3 PM regulations implement tighter FTP and supplemental FTP PM standards (US06 

cycle) at a full-useful life of 150,000 miles. The proposed Tier 3 FTP standard is 3 mg/mi, and the US06 

standard is 10 mg/mi for passenger cars and 20 mg/mi for light-duty trucks. In order to achieve the 

proposed Tier 3 standards, the US EPA believes that current technology gasoline vehicles will need to 

have both lower emissions and improved engine and emission control durability. The Kansas City 

analysis showed that lubricating oil contributes significantly to PM emissions, and increases as vehicles 

age and deteriorate (1). Assuming that such deterioration would continue in the absence of Tier 3, to 

achieve Tier 3 PM standards at full-useful life, the EPA anticipates that vehicle manufactures may 

implement a variety of strategies, including reducing lubricating oil consumption. 

For quantifying the emissions reductions in the NPRM analysis, only the impact of reduction in 

lubricating oil is calculated. The Kansas City analysis estimated that 42% of the fleet-average OC 

emission rates are attributed to lubricating oil emissions, and 25% of the total PM emission rates are 
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attributed to lubricating oil emissions (1). The EPA analysis assumes that a comparable average 

reduction in OC and PM will be achieved for Tier 3 vehicles over the lifetime of the vehicles. 

The EPA analysis used the fleet-weighted PM contribution from the Kansas City analysis because many 

of the newer vehicles in the Kansas City study had not reached full deterioration. In the absence of PM 

data on deteriorated Tier 1 and Tier 2 vehicles, the EPA analysis assumed that the relative contribution 

of PM emissions from older vehicles observed in the Kansas City study would continue for Tier 2 

vehicles. The EPA analysis assumed that all the PM contributed oil emissions were eliminated under the 

Tier 3 scenario. This was deemed to be a reasonable assumption because the EPA anticipated other 

emission reduction strategies would be implemented in Tier 3 vehicles which were not accounted for in 

this analysis. Other PM reduction strategies include reducing over-fueling at cold start and high-load 

conditions. 

Implementation of Emission Reductions in MOVES

The reduction of lubricating oil-derived PM in MOVES was modeled as a reduction in OC emissions, such 

that the PM is reduced by 25%. Table 3 shows the MOVES OC needed to achieve the 25% PM reductions 

from lower OC rates. In MOVES, OC was estimated as the non-EC component of PM from the Kansas City 

Light-Duty Vehicle Emission Study. As such, the ‘MOVES OC’ rates include the ‘OC’ as well as non-carbon 

components of PM, metals, and ions. Due the definition of ‘MOVES OC’, to achieve similar reductions in 

total PM through reductions in OC, the change in ‘MOVES OC’ is less than OC lubricating-oil contribution 

estimated in the Kansas City analysis.

Table 3. Estimated PM reduction due to improved Tier 3 control in MOVES

Source MOVES OC/PM MOVES OC reductions PM reductions

start car 66% 38% 25%

start truck 68% 37% 25%

running car 82% 30% 25%

running truck 93% 27% 25%

The calculated reductions for starts and running MOVES OC emission rates range from 27% to 38%. Due 

to the uncertainty in the analysis, the EPA chose to represent the Tier 3 control with a 30% reduction in 

the OC rates in MOVES for both start and running process, and for all ages of Tier 3 vehicles. 

No differences were estimated for the different sources (cars and trucks) or for different emission 

processes (start and running). The Kansas City analysis estimated the lubricating oil contribution to PM 

emissions by pooling the passenger cars and trucks together. The 30% reduction is applied equally 

across all operating modes. The oil analysis was conducted over individual and filter composites of the 

LA-92 cycle, and the lubricating oil contribution could not be estimated separately for cold start, hotstart or hot-running conditions.

At the time of this analysis, the EPA had no available data to evaluate the impact of Tier 3 on mediumduty gasoline vehicles that are regulated by the Tier 3 standards. The PM emissions rates in MOVES from
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medium-duty gasoline vehicles have previously been adjusted from the light-duty PM emission rates. 

Thus, the same 30% reduction in OC emission rates was also applied to medium-duty gasoline vehicles.

Modeling Tier 3 PM Impacts in the Final Rule Making

A particulate matter test program was underway at the time of this analysis at the U.S. EPA National 

Vehicle Fuel & Emission Laboratory on Tier 2 vehicles aged to 120,000 miles. The test program was being 

conducted to assess the feasibility of the Tier 3 standards on current and future technology vehicles. The 

modeled benefit of the Tier 3 rule will be revisited when the test program is complete. 

References:

1. Darrell B. Sonntag, Chad R. Bailey, Carl R. Fulper, and Richard W. Baldauf. Contribution of 

Lubricating Oil to Particulate Matter Emissions from Light-Duty Gasoline Vehicles in Kansas City. 

Environmental Science & Technology 2012, 46(7), 4191-4199.