Emissions of HFC-134a fromLight-Duty Vehicles in CaliforniaRichard Vincent, Kevin Cleary,Alberto Ayala, and Richard CoreyResearch DivisionCalifornia Air Resources Board6th SAE Automotive AlternateRefrigerant Systems SymposiumJune 29 - July 1, 2004SAE 2004-01-2256Overview• ARB’s Activities in Mobile AC• Information on HFC Emissions• ARB’s Approach to Estimation• Results of Analysis• Caveats and ComparisonsAB 1493(Pavley, 2002)• ARB must set standards on GHG emissionsfrom new LDVs, 2009 et seq. models.• Maximize emission reductions for GHGs atacceptable cost to consumer.• No specific treatment of HFCs is required.• Proposal: GHG std. on vehicle; credit forlow-leak systems & change of refrigerant• Workshop July 7 (on web)• Board hearing Sept 2004ARB Staff Activities• SAE ARCRP Phase II• EPA Enhanced HFC-134a SystemDevelopment Effort• 2005 MACS Summit in Sacramento(ARB will sponsor)Three Modes of EmissionModeNatureWhen occursLeakagegradual&during “life”continuousAccidentalsudden ran- during lifereleasesdom eventsScrappingone event end of lifereleaseEmission MeasurementsLeakage– Ford (Siegl): diurnal loss tests, cold vehicles– EMPA (Stemmler): Swiss tunnel studyLeakage + Accidental– Öko-Recherche: state-of-charge, 276 in-(Schwarz) use European vehiclesProbable Factors in Leakage• Make, model, and year(differentdesigns, materials & assembly practices)• Variability among vehicles• Age&accumulated hours of operation• Under-hood temperature• Compressor on vs. off• Maintenance practicesAlternative:Lifetime Emissions by Mass Balance• Over a vehicle’s life,Emissions = Net inputs= initial charge + recharges-amount recovered at end• Net inputs: only ~3 discrete events• Data are accessible for many vehiclesLifetime Emission ModelLE = C * (1 - g + N*f)C -- capacity (kg)“1” -- initial chargeg -- fraction of charge recovered atscrappingN -- number of rechargesf -- fraction of capacity rechargedOur Data Sources 

# Number of recharges:12,000vehicles in9 fleets;surveys of966vehicle owners



# System capacity & 

# amount per recharge:288 evacuations&recharges 

# End-of-life recovery: survey of dismantlers, discussions with EPA&reclaimers



# Lifetime:EMFAC emission model (16 yrs)Estimating N (number ofrecharges) from Fleet DataN ́i:the fraction of HFC-134a vehicles of age ithat receive recharges during a yearEstimated as:[# recharges in 12 mo./ # vehicles]i(i = age)(recharges per16-yr life)∑≈161N)yr/veh/esargrech('NAge PatternFig. 4 Events by Age0.0000.0200.0400.0600.0800.1000.1200.1400 2 4 6 8 10 12 14 16 18 20Age, yrs

FrequencyN' from fleet dataMACS repair counts in 2000MACS data are normalized by onroad populations & adjusted forscaleaEvents vs. AgeSurveys of 966 Vehicle OwnersTotal Recharges per Vehicle(lifetime to 2003)0.000.200.400.600.801.001.201993 1994 1995 1996 19971998 1999 2000 2001 2002 2003Model YearCal/EPA surveyUSEPA survey(678 veh)(288 veh)Cumulative RechargesRecharges during Life to Date0.00.20.40.60.81.01.20 2 4 6 8 10 12 14 16 18Age, years

Avg Events per VehicleSum of N'Combined survey datafrom regression of N'2 std. dev.Average ResultsN -- from12,000vehicles: 1 

# recharge over 16 yrsC -- mean of288data: 

# 951 gramsf -- mean of288data: 

# .52g -- set to 

# 8.5%(50% recovery)--------------------------= 1.36 kg (85 g/yr))fà*Nàgà(*CàEL^+−≈1The “12-Oz. Can” Question• Our result does not reflect:– excess emissions from DIY repairs(release of system contents)– excess from repeated top-offs w/oleak repairs (R134a 

# & 

# R12systems)• Total excess <50 g/yr/veh(including R134a into R12 vehicles)ComparisonsLoss, grams/yrMeasured leak rates*(Ford)26Long-term loss(Öko-Recherche)^53Tunnel study (Swiss) 123-----------------------------ARB analysis 85* vehicles & AC’s not operating^ early period of vehicle lifeSummary of Analysis• Lifetime emission estimate based onmass balance; used no data on loss rate• Used input data from 1000’s of Californiavehicles• Result compatible with empirical data• Provides sound regulatory baselineLimitations• Our data are specific to the vehicle fleetof 2003; biased toward US brands• Methodology does not allow identifyingmodel-year effects• Does not distinguish among lossmechanismsPlanned Future Work• Tunnel study in California• Develop SHED testing• Quantify retail sales HFC-134a(DIY emissions)• SAE & EPA R&D projects