Scientific Assessment of Ozone Depletion: 2010

Chapter 1 Scientific Summary

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Chapter 1 Authors and Contributors

Scientific Summary Chapter 1: Ozone-Depleting Substances (ODSs) and Related Chemicals

The amended and adjusted Montreal Protocol continues to be successful at reducing emissions and atmospheric abundances of most controlled ozone-depleting substances (ODSs).

Tropospheric Chlorine

Stratospheric Chlorine and Fluorine

Tropospheric Bromine

Stratospheric Bromine

Very Short-Lived Halogenated Substances (VSLS)

VSLS are defined as trace gases whose local lifetimes are comparable to, or shorter than, tropospheric transport timescales and that have non-uniform tropospheric abundances. In practice, VSLS are considered to be those compounds having atmospheric lifetimes of less than 6 months.

Equivalent Effective Stratospheric Chlorine (EESC)

Figure S1-1. Stratospheric EESC Relative to Peak Abundances Versus Time

Figure S1-1
Stratospheric EESC derived for the midlatitude and polar stratospheric regions relative to peak abundances, plotted as a function of time. Peak abundances are ~1950 ppt for the midlatitude stratosphere and ~4200 ppt for the polar stratosphere. Percentages shown to the right indicate the observed change in EESC by the end of 2008 relative to the change needed for EESC to return to its 1980 abundance. A significant portion of the 1980 EESC level is from natural emissions.

EESC is a sum of chlorine and bromine derived from ODS tropospheric abundances weighted to reflect their potential influence on ozone in different parts of the stratosphere. The growth and decline in EESC varies in different regions of the atmosphere because a given tropospheric abundance propagates to the stratosphere with varying time lags associated with transport. Thus the EESC abundance, when it peaks, and how much it has declined from its peak vary in different regions of the atmosphere.

Emission Estimates and Lifetimes

Other Trace Gases That Directly Affect Ozone and Climate

Other Trace Gases with an Indirect Influence on Ozone

Direct Radiative Forcing

The abundances of ODSs as well as many of their replacements contribute to radiative forcing of the atmosphere. These climate-related forcings have been updated using the current observations of atmospheric abundances and are summarized in Table S1-1. This table also contains the primary Kyoto Protocol gases as reference.

Table S1-1. Direct radiative forcings of ODSs and other gases, and their recent changes.

Specific Substance or Group of SubstancesDirect Radiative Forcing (2008), milliWatts per square meter (mW/m2)Change in Direct Radiative Forcing (2003.5-2008.5), mW/m2
CFCs *262-6
Other ODSs *15-2
HCFCs *458
HFCs #,a125
HFC-23 #40.9
CO2 #1740139
CH4 #5004
N2O #17012
PFCs #5.40.5
SF6 #3.40.7
Sum of Montreal Protocol gases *3220
Sum of Kyoto Protocol gases #2434163

* Montreal Protocol Gases refers to CFCs, other ODSs (CCl4, CH3CCl3, halons, CH3Br), and HCFCs.
# Kyoto Protocol Gases (CO2, CH4, N2O, HFCs, PFCs, and SF6).
a Only those HFCs for which emissions arise primarily through use as ODS replacements (i.e., not HFC-23).