We use a regional-scale, three-dimensional atmospheric model to evaluate U.S. air quality effects that would result from replacing HFC-134a in automobile air conditioners in the U.S. with HFO-1234yf. Although HFO-1234yf produces tropospheric ozone, the incremental amount is small, averaging less than 0.01% of total ozone formed during the simulation. We show that this production of ozone could be compensated for by a modest improvement in air conditioner efficiency. Atmospheric decomposition of HFO-1234yf produces trifluoroacetic acid (TFA), which is subject to wet and dry deposition. Deposition and concentrations of TFA are spatially variable due to HFO-1234yf's short atmospheric lifetime, with more localized peaks and less global transport when compared to HFC-134a. Over the 2.5 month simulation, deposition of TFA in the continental U.S. from mobile air conditioners averages 0.24 kg km(-2), substantially higher than previous estimates from all sources of current hydrofluorocarbons. Automobile air conditioning HFO-1234yf emissions are predicted to produce concentrations of TFA in Eastern U.S. rainfall at least double the values currently observed from all sources, natural and man-made. Our model predicts peak concentrations in rainfall of 1264 ng L(-1), a level that is 80x lower than the lowest level considered safe for the most sensitive aquatic organisms.

Ab initio calculations have been performed at the MP2/6-31G** level for the series of fluorinated ethanes, C 2 H n F 6-n , n ) 0-5. The resulting geometries, dipole moments, vibrational frequencies, and absolute infrared intensities are reported for stable conformers of the series, including both anti and gauche species, together with their energy differences, for 1,2-difluoroethane, 1,1,2-trifluoroethane, and 1,1,2,2-tetrafluoroethane. The results are compared to available experimental data. In particular, because of the importance of members of this series as potential CFC substitutes, the accuracy of the computational results for infrared frequencies and intensities is discussed, including the dependence on basis set, for calculations at the MP2 level of the theory.

Abstract. We have employed the radiative forcing function recently computed by Pinnock et al. [1995], in conjunction with infrared cross sections and vibrational frequencies calculated with ab initio quantum-mechanical methods, to estimate the instantaneous infrared radiative forcing terms-'•ot of a number of CFC substitutes and their atmospheric reaction products. The computed quantities-•>•,t are compared with those obtained by Pinnock et al. [ 1995] employing experimental infrared spectra. In particular, Gaussian-92 TM software has been utilized, at the MP2/6-31G** level of theory, to provide computational estimates of these quantities. Our results agree with the former, with a mean and a standard deviation of the difference of +3% and 15%, respectively. An error analysis is provided to assess the utility of the method. The capability of quantum-mechanical computational methods to explore structural trends in radiative and physicochemical properties is exploited for the molecular systems examined here.

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.