Abstract. This paper describes the sources contributing to two seasonal peaks in colunmar SO2 amounts measured with a Brewer spectrophotometer at Thessaloniki, Northern Greece since 1982. The SO2 Brewer measurements combined with those at ground level, meteorological analysis and numerical simulations provide estimates on the contribution of local and remote sources to the SO2 column. It is shown that more than 50% of the observed SO2 column can be attributed to ligniteburning sources in Bulgaria, Romania and former Yugoslavia, this percentage rising to 70% at periods with NE flow at 850 hPa. Winds from the NW-N-NE contribute around 60% to the observed mean SO2 column during winter and 75% during the summer. When including all wind directions at 850 hPa, the Greek sources, including the lignite-burning power plant complexes to the WSW of the city, contribute around 40% to the SO2 colurn. These results are in qualitative agreement with independent observations from inversion of GOME measurements.

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This paper provides a new look at the spatial and temporal distribution of monthly mean residuals of the global ozone field following the two large volcanic eruptions of El Chichon and Pinatubo. The residuals have been calculated after careful removal of the components of known oscillations from the monthly mean total ozone records. The removal eliminated not only the well‐established Quasi Biennial Oscillation but also the robust pattern of all El Nino/Southern Oscillation events active during the period of study. These residuals are composed by a “climatic noise” term plus a possible volcanic signal whose amplitude is in some agreement with model calculations particularly over low and middle latitudes following the recent Pinatubo eruption. However, this analysis shows no ozone deficiency following El Chichon over the southern hemisphere and this result can be explained by the prevailing winds in the lower stratosphere in the post‐El Chichon period as described in the text. Quantitatively speaking, the magnitude of the observed ozone deficiency which can be attributed to the volcanic effect is smaller than reported earlier either from theory or observations, and ranges between 2 and 4% at the equatorial latitudes up to about 5% over the middle and high latitudes, including the noise term, and lasting for a period of months after the eruption. These deficiencies are also larger than the anticipated error caused by the aerosol‐contaminated radiances, as reported by other scientists. The present results, although not precluding a transient volcanic component following large volcanic eruptions in the ozone records, do show, however, that our understanding of the physical mechanisms involved is probably still incomplete.