Estimated 2017 Refrigerant Emissions of 2,3,3,3- tetrafluoropropene (HFC-1234yf) in the United States Resulting from Automobile Air Conditioning STELLA PAPASAVVA,* ,† DEBORAH J. LUECKEN, ‡ ROBERT L. WATERLAND, § KRISTEN N. TADDONIO, | AND STEPHEN O. ANDERSEN | Stella Papasavva Consulting, Royal Oak, Michigan 48073, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27709, E. I. du Pont de Nemours and Co., Inc. Wilmington, Delaware 19880, U.S. Environmental Protection Agency, Washington, DC 19805 Received July 15, 2009. Revised manuscript received October 19, 2009. Accepted October 26, 2009. In response to recent regulations and concern over climate change, the global automotive community is evaluating alternatives to the current refrigerant used in automobile air conditioning units, 1,1,1,2-tetrafluoroethane, HFC-134a. One potential alternative is 2,3,3,3-tetrafluoropropene (HFC-1234yf, also known as HFO- 1234yf). We have developed a spatially and temporally resolved inventory of likely future HFC refrigerant emissions from the U.S. vehicle fleet in 2017, considering regular, irregular, servicing, and end-of-life leakages. We estimate the annual leak rate emissions for each leakage category for a projected 2017 U.S. vehicle fleet by state, and spatially apportion these leaks to a 36 km square grid over the continental United States. This projected inventory is a necessary first step in analyzing for potential atmospheric and ecosystem effects, such as ozone and trifluoroacetic acid production, that might result from widespread replacement of HFC-134a with HFC-1234yf. Introduction Vehicle air conditioning is a significant and growing source of greenhouse gas (GHG) pollution. Current mobile air conditioning (MAC) systems use hydrofluorocarbon (HFC)- 134a (1,1,1,2-tetrafluoroethane), which has a 100-yr global warming potential (GWP) of 1,430. MAC is the largest and most emissive sales market for HFC-134a. The use of MAC systems also consumes significant quantities of fuel as compared to similar driving conditions without operating the air conditioning. Current vehicle test procedures evaluate the differential fuel overconsumption due to MAC on conditions with windows closed. Recent life cycle GHG assessment studies (1) and previous work performed at the National Renewable Energy Laboratory (NREL) (2) have found that vehicle air conditioning accounts for up to 7% of motor vehicle fuel use in the U.S. and up to 20% in vehicles sold in climates that are hotter and more humid than average, such as those found in India and China (1, 2). However, turning off the air conditioner and rolling-down the windows also decreases fuel economy due to increased air drag but this scenario is not considered in these studies (1, 2). In response to concern about climate change, policy- makers around the world are taking action to reduce GHG pollution from MACs. In 2002, the U.S. State of California passed Assembly Bill 1493, which requires the California Air Resources Board (CARB) to develop new regulations to reduce GHG emissions from new motor vehicles including MACs. In 2006, the European Commission issued Directive 2006/ 40/EC (commonly known as the F-Gas Directive) (3), which requires new types of air-conditioned cars sold in the EU to have a refrigerant with a GWP of 150 or less starting in 2011, and all new vehicles to have a refrigerant with a GWP of 150 or less by 2017. In 2009, President Obama announced new national fuel efficiency standards with the aim of reducing U.S. vehicle GHG emissions (4). When fully implemented, this policy will provide incentives to reduce both refrigerant and tailpipe GHG emissions. International automotive manufacturers and their sup- pliers responded to this global regulatory activity by examin- ing many alternative lower GWP refrigerants including carbon dioxide (CO 2 , GWP ) 1); hydrocarbons (GWP < 10); HFC- 152a (1,1-difluoroethane, CH 3 CHF 2 , GWP ) 122); and HFC- 1234yf (2,3,3,3-tetrafluoropropene, CH 2 dCFCF 3 , GWP ) 4). The automotive community is nearing a final decision to select HFC-1234yf (also known as HFO-1234yf) to replace HFC-134a, and the U.S. Environmental Protection Agency’s Mobile Air Conditioning Climate Protection Partnership (USEPA MACCPP) is working to rapidly implement the transition from HFC-134a to HFC-1234yf worldwide. The selection of HFC-1234yf was based on comprehensive studies performed by chemical suppliers, technical associa- tions, environmental authorities, and industry-government partnerships. These reports included sophisticated life-cycle climate performance (LCCP) model studies which determined that HFC-1234yf systems will result in the lowest carbon footprint of all the proposed refrigerant alternatives (1) and comprehensive risk assessments that showed HFC-1234yf refrigerant poses the fewest overall safety risks compared to other refrigerant alternatives (5), taking into account its generally low overall human and environmental toxicity and mild flammability. Laboratory and smog chamber experi- ments have determined that HFC-1234yf has an estimated atmospheric lifetime of around 11 days with respect to hydroxyl radical reaction (6), decreasing to 6.6 days when all other reactions are also taken into account. HFC-1234yf has a zero stratospheric ozone-depletion potential and a 100-yr GWP of 4.4 (7). While HFC-1234yf’s relatively short atmospheric lifetime leads to a desirably low GWP, this also means that it has the potential to form ozone and other chemical species of concern in the troposphere. Ground-level ozone continues to be a serious problem in the United States and throughout the world (8), reaching levels in many places that can pose serious health effects. Concerns have also been raised about the potential effects of other chemical byproducts including trifluoroacetic acid and hydrofluoric acid. The tendency of HFC-1234yf to react faster than HFC-134a and hence closer to sources of emissions, increases the importance of un- derstanding the distribution of emissions on smaller geo- graphic scales than required for longer-lived refrigerants. * Corresponding author e-mail: greengem09@gmail.com. † Stella Papasavva Consulting. ‡ U.S. Environmental Protection Agency, Research Triangle Park, NC. § E. I. du Pont de Nemours and Co., Inc. | U.S. Environmental Protection Agency, Washington, DC. Environ. Sci. Technol. 2009 43, 9252–9259 9252 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 24, 2009 10.1021/es902124u CCC: $40.75  2009 American Chemical Society Published on Web 11/12/2009