The word about ozone.

The world's top atmospheric scientists mixed bad and good news when they released a report last week on the state of the ozone layer. The international panel of 226 researchers confirmed that record ozone depletions have occurred in recent years and should worsen in the next few years as concentrations of chlorine and bromine pollution peak in the stratosphere. On a brighter note, a 1987 treaty has started to curb use of the pollutants and should permit the ozone layer to recover over the next 50 years, provided that countries uphold the provisions of the agreement.

The Ozone Assessment Panel - sponsored by the United Nations' Environment Program and the World Meteorological Organization - noted that concentrations of ozone around the globe reached record lows in 1992 and 1993. The springtime Antarctic ozone hole also set records in 1992 and 1993 for the biggest area and the lowest ozone values. Since then, global ozone concentrations have partially recovered, to a point more in line with the expected slow rate of deterioration. Many researchers believe the extreme changes resulted from volcanic debris lofted into the stratosphere by Mount Pinatubo's eruption in 1991 (SN: 4/24/93, p.260). These particles of sulfuric acid helped speed up ozone destruction by chlorine and bromine, according to the panel.

While amounts of these pollutants continue to increase in the atmosphere, the rate of buildup has slowed in recent years, thanks to international controls mandated by the Montreal Protocol of 1987 and subsequent amendments. As the concentrations grow, ozone depletions should worsen. But stratospheric amounts of these chemicals should actually start to drop after peaking in 3 to 5 years, permitting the ozone layer to begin a slow recovery, the panel reports.