The 
following
 supplementary
 material
 provides
 additional
 details
 about
 our
 ozone
 depletion
potential,
 ODP, calculations,
 factors
 affecting
 the
 ODP 
of
 N₂O,
 uncertainties
 unique
 to 
the
 calculation
 of
 the
 ODP
 of
 N₂O,
 our
method
 of
 inferring 
N₂O
 emissions,
 and
 a
comparison
 of 
the
 contributions
 of
 the
 sectoral 
N₂O 
emissions
 with
 the
  emissions
 of
 methyl
 bromide.

By comparing the ozone depletion potential–weighted anthropogenic emissions of N2O with those of other ozone-depleting substances, we show that N2O emission currently is the single most important ozone-depleting emission and is expected to remain the largest throughout the 21st century. N2O is unregulated by the Montreal Protocol. Limiting future N2O emissions would enhance the recovery of the ozone layer from its depleted state and would also reduce the anthropogenic forcing of the climate system, representing a win-win for both ozone and climate.

Ozone-depleting substances emitted through human activities cause large-scale damage to the stratospheric ozone layer, and influence global climate. Consequently, the production of many of these substances has been phased out; prominent examples are the chlorofluorocarbons (CFCs), and their intermediate replacements, the hydrochlorofluorocarbons (HCFCs).

The year is 2065. Nearly two-thirds of Earth's ozone is gone -- not just over the poles, but everywhere. The infamous ozone hole over Antarctica, first discovered in the 1980s, is a year-round fixture, with a twin over the North Pole. The ultraviolet (UV) radiation falling on mid-latitude cities like Washington, D.C., is strong enough to cause sunburn in just five minutes.

The present assessment deals with the results of previously undertaken investigations. These repeatedly give reasons for concern for potential effects, but relatively little progress has been made in quantifying these effects. The more the investigators look into the problems, the more the complexity becomes apparent. Nevertheless, the knowledge is accumulating

Industrial chlorofluorocarbons that cause ozone depletion have been phased out under the Montreal Protocol. A chemically-driven increase in polar ozone (or “healing”) is expected in response to this historic agreement. Observations and model calculations taken together indicate that the onset of healing of Antarctic ozone loss has now emerged in September. Fingerprints of September healing since 2000 are identified through (i) increases in ozone column amounts, (ii) changes in the vertical profile of ozone concentration, and (iii) decreases in the areal extent of the ozone hole.

Ozone depleting substances (ODSs) controlled by the Montreal Protocol are potent greenhouse gases (GHGs), as are their substitutes, the hydrofluorocarbons (HFCs). Here we provide for the first time a comprehensive estimate of U.S. emissions of ODSs and HFCs based on precise measurements in discrete air samples from across North America and in the remote atmosphere. 

The Executive Summary contains key summaries from the Scientific Assessment of Ozone Depletion: 2006, prepared during 2005-2006 by the Scientific Assessment Panel of the U.N. Montreal Protocol on Substances that Deplete the Ozone Layer.