This paper focuses on the analysis of thermopower plants emissions with regard to a new indicator, SONOX (SO from SO2 and NOX from NOx), which is symbolized by Sigma. Based on this method, analysis is accomplished for several Romanian thermopower plants fuelled by lignite. Conclusions are drawn concerning the possibilities of reduction of the reaction agents for desulphurisation of the flue gas exhausted by the thermopower plants. (C) 2004 Elsevier Ltd. All rights reserved.