Influence of sulfur dioxide trends on Dobson measurements and electrochemical ozone surroundings

摘要

Total ozone measurements have been performed at Uccle (50$DGR@48'N, 4$DGR@21'E) with Dobson spectrophotometer 40 since August 1971 and with Brewer instrument 16 since July 1983. The reduced thickness of sulfur dioxide (SO$-2$/) as calculated from measurements with the Brewer spectrophotometer shows a decreasing trend that is in good agreement with the trend of in situ measurements of SO$-2$/ density near the ground in the urban area of Brussels. From the mean annual variation of the ratio of both variables the corresponding correction for SO$-2$/ interference of the Dobson instrument data was calculated on a month-by-month basis. From a comparison of the total ozone trends before and after SO$-2$/ correction, it appeared that over the whole time period (August 1971 to May 1993) the SO$-2$/ decrease at Uccle has induced a fictitious Dobson total ozone trend that amounts to a mean value of $MIN@1.47% per decade. More than half of the stations which have been used in the past in ozone trend studies are located within an urban area with a population of over 100,000 and are in consequence possibly affected by air pollution.