Ozone nightmates

GLOBAL levels ofozone, which shields the from the Sun's harmful ultravioletradiations, have fallen to a recordover the past 2 years. But the worstR to come, according to the report ofan international scientific panel.However, a redeeming feature of the1994 Assessment Panel report, mandated under the 1987 Montreal Protocol onSubstances that Deplete the OzoneLayer, is that the emissions of chemicalsharmful to ozone have also gone down.

The 'panel was set up under the auspices, of the Geneva-based WorldMeteorological Organization (WMO)and the United Nations EnvironmentProgramme (UNEP) in Nairobi. It comprised 226 atmospheric science experts,drawn from 29 countries.

The report reveals that the atmospheric growth rates of human-made compounds that deplete the ozone layer, such as chlorofluorocarbons (CFCs), used in refrigeration, and halons, used in fire extinguish ers, have slowed in recent years following reductions in global emissions of these compounds. Says UNEP executive director Elizabeth Dowdeswell, "While the 1994 Assessment Panel report confirms that we are heading in the right direc tion, we cannot afford to be complacent. The line that divides complacency from cata strophe is very thin and now is not the time to break that momentum."

The report lists 4 steps that willsteepen the fall from the peak halocarbon levels in the early decades of thenext century. reductions in emissions ofmethyl bromide used as a soil and cropfumigant, reductions in emissions ofhydrochlorofluorocarbons, the complete recapture (as opposed to recycling) Of CFcs, and halons banked in existing equipment.
Maximum lossDuring the winters of 1992 and 1993,the Antarctic ozone"hole" became bigger anddeeper. Satellites and balloon-borne and groundbased monitoring instru-ments revealed that ozoneover the Antarctic wasdepleted by -more than 99per cent between theheights of 14 to 19 krn inOctober 1992 and 1993.Over the same period,ozone levels over populated regions of the northernhemisphere also Registered a record low. The loss was 10 percent in 1992 and 7 per cent in 1993 overthe ozone levels in the late '60s, according to G L Manney of the CaliforniaInstitute of Technology and his colleagues (Nature, Vol 370, No 6489).

The panel report contends that thisrecord depletion probably owed, at leastin part, to chemical processes linked tothe 1991 eruption ofMount Pinatubo in thePhilippines.

Scientists reckon thatpeak global ozone depletions would occur around1998, mainly because ofthe past emissions. Thereafter, the levels of ozonedepleting chlorine andbromine are expected toslowly decrease and theozone layer is expected torecover in about 50 years.

Nelson I Sabogal, anofficer at, UNEWS OzoneSecretariasNairobi, says that extrap olation of the rent trends 'suggests thatozone loss relative to the late '60sabout 13 per cent at northern midtudes in winter and spring - abowper cent above the current delevels. And it is estimated that imsouthern latitudes the ozone loss11 per cent of the level in the late '60s.

According to UNEP, large incuv radiation on the earth's surfacebeen observej in the Antarctic andsouthern part of South Americaspring and winter, when the ozoneis observed. Further, elevated Liat the mid to high latitudesobserved in the northern hemi1992 and 1993, corresponding low ozone levels in those yeamincrease in ov radiation, expertscould lead to an increase in skin cases and cataracts, especialivpeople residing in the mid-latitudes.