Proposed Short-Lived Climate Pollutant Reduction Strategy

levels of ozone pollution and provide additional climate, health, and other
benefits. 76,77,78
Regional ozone concentrations reflect contributions from both ozone formed from
criteria pollutant emissions (NO X and volatile organic compounds [VOCs]) on a regional
scale, and ozone transported on hemispheric scales (global background levels of
ozone). Due to its low reactivity, methane emissions do not affect regional scale ozone
production that occurs over hours to days. However, regional methane emissions which
are fairly well-mixed in the atmosphere contribute to the global abundance of methane,
which in turn contributes to global background levels of ozone. About two-thirds of the
rise in global levels of tropospheric background ozone can be attributed to methane
emissions. Studies have also shown that the global background ozone concentrations
can approach 40 parts per billion and have been increasing in recent years. Increases
in background ozone make it harder to attain the health-based ambient air quality
standards set by U.S. EPA and California.
C. Fluorinated Gases (Hydrofluorocarbons)
Hydrofluorocarbons (HFCs) are synthetic gases used in refrigeration, air conditioning,
insulating foams, solvents, aerosol products, and fire protection. They are primarily
produced for use as substitutes for ozone-depleting substances, including
chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which are being
phased out under the Montreal Protocol. Currently, HFCs are a small fraction of the
total climate forcing, but they are the fastest growing source of GHG emissions in
California and globally, primarily driven by the increased demand for refrigeration and
air conditioning.
HFCs vary significantly in their ability to influence climate. Their differing ability is
mostly due to differences in their atmospheric lifetimes, which determine how much they
accumulate in the atmosphere. The mix of HFCs in current use, weighted by usage
(tonnage), has an average atmospheric lifetime of 15 years. HFCs are also potent
GHGs, with a warming effect hundreds to thousands of times more powerful than CO 2.
The average 100-year GWP of the current mix of HFCs being used is about 1600, and
the average 20-year GWP is about 3500. The major concern with respect to HFCs is
that their contribution to climate forcing is expected to increase rapidly in the future as
76 Fiore, A. M., J. J. West, L. W. Horowitz, V. Naik, and M. D. Schwarzkopf (2008) Characterizing the
tropospheric ozone response to methane emission controls and the benefits to climate and air quality, J.
Geophys. Res., 113, D08307, doi:10.1029/2007JD009162.
77 West, J. J., A. M. Fiore, L. W. Horowitz, and D. L. Mauzerall (2006), Global health benefits of mitigating
ozone pollution with methane emission controls, Proc. Natl. Acad. Sci. U.S.A., 103, 3988–3993.
78 Fiore, A. M., F. J. Dentener, O. Wild, C. Cuvelier, M. G. Schultz, P. Hess, C. Textor, M. Schulz, R. M.
Doherty, L. W. Horowitz, I. A. MacKenzie, M. G. Sanderson, D. Shindell, D. S. Stevenson, S. Szopa, R.
Van Dingenen, G. Zeng, C. Atherton, D. J. Bergmann, I. Bey, G. Carmichael, W. J. Collins, B. Duncan, G.
Faluvegi, G. Folberth, M. Gauss, S. Gong, D. Hauglustaine, T. Holloway, I. S. A. Isaksen, D. Jacob, J. E.
Jonson, J. W. Kaminski, T. J. Keating, A. Lupu, E. Marmer, V. Montanaro, R. J. Park, G. Pitari, K. J.
Pringle, J. A. Pyle, S. Schroeder, M. G. Vivanco, P. Wind, G. Wojcik, S. Wu, and A. Zuber (2009),
Multimodel estimates of intercontinental source-receptor relationships for ozone pollution, J. Geophys.
Res., 114, D04301, doi:10.1029/2008JD010816.
38 April 11, 2016