An ongoing probe by the Department of Environment, Forestry and Fisheries (DEFF) to determine the cause of the high levels of air pollution reported in Mpumalanga and Gauteng during the week of February 11 to 17 has determined that sulphur dioxide (SO2) levels were in compliance with ambient air-quality standards across all stations during the week, but that levels of hydrogen sulphide (H2S) had been elevated at times during the week. The probe followed reports of persistent, unpleasant smells in the western parts of Mpumalanga and eastern Gauteng during that week. The DEFF said the sulphurous stench was most likely a combination of elevated levels of SO2 and H2S.