Emissions of HFC-134a 

Light-Duty Vehicles in C

Richard Vincent, Kevin Clea

Alberto Ayala, and Richard C

Research Division

California Air Resources Bo

6th SAE Automotive Altern

Refrigerant Systems Sympos

June 29 - July 1, 2004

SAE 2004-01-2256
Overview

• ARB’s Activities in Mobile • Information on HFC Emi• ARB’s Approach to Estim• Results of Analysis• Caveats and Comparison
AB 1493 (Pavley, 20

• ARB must set standards on GH

from new LDVs, 2009 et seq. 

• Maximize emission reductions 

acceptable cost to consumer.

• No specific treatment of HFCs • Proposal: GHG std. on vehicle

low-leak systems & change of 

• Workshop July 7 (on web)• Board hearing Sept 2004
ARB Staff Activitie

• SAE ARCRP Phase II• EPA Enhanced HFC-134a 

Development Effort

• 2005 MACS Summit in Sa

(ARB will sponsor)
Three Modes of Emis

Mode Nature W

Leakage gradual 

& d

continuous 

Accidental sudden ran- dreleases dom events 

Scrapping one event e

release
Emission Measurem

Leakage

– Ford (Siegl): diurnal loss tests, – EMPA (Stemmler): Swiss tunne

Leakage + Accidental

– Öko-Recherche: state-of-char

(Schwarz) use Europea
Probable Factors in Le

• Make, model, and year (diff

designs, materials & assembly 

• Variability among vehicles• Age 

& accumulated hours o

• Under-hood temperature• Compressor on vs. off • Maintenance practices 
Alternative:

Lifetime Emissions by Ma

• Over a vehicle’s life,

Emissions = Net inputs

= initial charge + 

- amount recov

• Net inputs: only ~3 discrete • Data are accessible for many 
Lifetime Emission M

LE = C * (1 - g + N*f

C -- capacity (kg)

“1” -- initial charge

g -- fraction of charge recov

scrapping

N -- number of recharges

f -- fraction of capacity rech
Our Data Sources

Number of recharges : 12,000 v

9 fleets; surveys of 966 vehic

System capacity 

& amount per 

288 evacuations 

& recharges 

End-of-life recovery : survey of 

lers, discussions with EPA 

& r

Lifetime : EMFAC emission mode
Estimating N (numbe

recharges) from Fleet 

N

 ́i: the fraction of HFC-134a veh

that receive recharges during Estimated as: 

[# recharges in 12 mo./ # 

(i = age)

(re

∑ 1

≈

16

1

N'(recharges

/veh

/yr

)

N
Age Pattern

Fig. 4 Events by Age

0.0000.0200.0400.0600.0800.1000.1200.140

0 2 4 6 8 10 12 14 

Age, yrs

Frequency

N' from fleet data MACS repair counts in 2

MACS data are normalized by onroad populations & adjusted for scale

a Events vs. Age
Surveys of 966 Vehicle 

Total Recharges per Vehicle

(lifetime to 2003)

0.000.200.400.600.801.001.20

1993 1994 1995 1996 1997 1998 1999 2000 200

Model Year

Cal/EPA survey USEPA survey

(678 veh) (288 veh)
Cumulative Rechar

Recharges during Life to Date

0.00.20.40.60.81.01.2

0 2 4 6 8 10 12 

Age, years

Avg Events per Vehicle 

Sum of N' Combined survey data

from regre

2 std. dev.
Average Results

N -- from 12,000 vehicles: 1 re

ove

C -- mean of 288 data: 951 gr

f -- mean of 288 data: .52g -- set to 8.5% (50% recove

-------------------

= 1.36 kg (85 g/

f)

à

N

*

à

C

*

(

gà

à

L

E

^

≈

1

−

+
The “12-Oz. Can” Que

• Our result does not reflect:

– excess emissions from DIY 

(release of system content

– excess from repeated top-o

leak repairs (R134a 

& R12 

• Total excess < 50 g/yr/veh 

(including R134a into R12 vehic
Comparisons

Lo

Measured leak rates* (Ford) 

Long-term loss (Öko-Recherche)

Tunnel study (Swiss) 

---------------------ARB analysis 

* vehicles & AC’s not operating

^ early period of vehicle life
Summary of Analy

• Lifetime emission estimate ba

mass balance; used no data o

• Used input data from 1000’s o

vehicles

• Result compatible with empiri• Provides sound regulatory bas
Limitations

• Our data are specific to the 

of 2003; biased toward US b

• Methodology does not allow 

model-year effects

• Does not distinguish among 

mechanisms
Planned Future Wo

• Tunnel study in California• Develop SHED testing• Quantify retail sales HFC

(DIY emissions)

• SAE & EPA R&D projects