Two months ago, scientists involved in the 17-nation European Arctic Stratospheric Ozone Experiment (EASOE) warned that ideal conditions for ozone depletion were occurring over the northern hemisphere (ENDS Report 205, p 8 ).
Analysis of their data has now shown that stations across Europe showed ozone levels 10-20% below average during December and January. Two stations, Hohenpeissenberg in Germany and Uccle in Belgium, reported record ozone losses of 10% and 18%, respectively. The European data are in broad agreement with satellite measurements made by NASA.
EASOE scientists believe that three factors contributed to the record. These were high concentrations of chlorine from CFCs and other pollutants, dust particles in the stratosphere from the Mount Pinatubo eruption, and unusual weather conditions.
Stratospheric chlorine levels will rise in the remaining years of this century before the benefits of the phase-out of ozone-depleting chemicals are realised.
The Mount Pinatubo eruption has increased stratospheric particles ten-fold, EASOE found. High particle concentrations correlated with low levels of NOX, which is believed to inhibit ozone destruction.
Anticyclonic weather conditions are known to be naturally associated with low levels of stratospheric ozone. The persistent anticyclone over western Europe this winter probably contributed to the very low ozone levels.
Meanwhile, despite the thinning of the ozone layer, monitoring has not shown any increase in ultra-violet radiation across Britain.
The National Radiological Protection Board (NRPB) has three monitoring stations in Oxfordshire, Glasgow and Leeds which have been operating since 1988. But the network was not designed to measure the effects of ozone depletion, and will be unlikely to register increased levels of UV until ozone thinning averages 10-20%, the NRPB believes.
The network was intended to study long-term changes across the broad range of UV wavelengths that cause sunburn. Natural variations in ozone thickness, air pollution and cloud cover all contribute to the variability in UV levels. Long-term measurements are therefore needed to establish the range of normal variation across the UK.
Although the NRPB believes there is a good case for monitoring targetted more specifically at the detection of possible changes in UV radiation as a result of ozone thinning, it has been unable to obtain funding.