Until recently, kraft pulp mills and their surrounding communities have been characterized by a continuous distinct foul odor caused predominantly by malodorous reduced sulfur compounds, often also called as total reduced sulfur (TRS). Substantial advances in emission control technology during the last decade have reduced sulfur emissions considerably. Unfortunately, the reduced sulfur compounds cause subjective odor nuisance at very low concentrations and therefore pulp mills, even with modern and efficient odor abatement systems, may cause foul odor in their surrounding communities. Further reduction of the TRS emission at a modern pulp mill will not be easily achieved due to the fact that all the previous major sources are already eliminated. In this new and more demanding situation, it is important to know how malodorous sulfur gases are formed in the pulping and combustion processes, and how emitted gases can be collected and destroyed. Furthermore, it is important to recognize the influence of the prevailing emission sources on the ground level ambient air concentration of the sulfur compounds. In this paper, the formation mechanism of the reduced sulfur compounds and the main principles of odor abatement systems are briefly presented. In addition, a method for combining emission source information and meteorological considerations to predict dispersion of the gaseous emission and to estimate ambient air concentration is described. The experimental part of the paper describes results from the plant audit, in which the relative importance of prevailing TRS emission sources was estimated by utilizing the gaussian model of the emission dispersion. In addition, reduced sulfur concentrations (measured with an automatic emission monitoring station) of the pulp mill's surrounding area were analyzed and the frequency of different reduced sulfur concentration categories was estimated. Finally, a suggestion of actions to eliminate (or at least minimize) both continuous and occasional odor occurrence in the surrounding community is presented.
