Effects of process changes on concentrations of individual malodorous sulphur compounds in ambient air near a Kraft pulp plant in Thunder Bay, Ontario, Canada

Abstract

Ambient air samples were collected at several locations in the community around a major Canadian pulp and paper plant over a period of several months, before and after major process changes. These changes, which occurred in the spring of 2006, included the closure of one of two Kraft pulp mills on site and the shutting down of a chemical recovery boiler and associated black liquor oxidation systems. The facility currently operates one Kraft mill producing both hardwood and softwood market pulp and a two machine paper mill with thermomechanical and deinking pulp mills. All ambient air samples were collected downwind from the plant in Teflon bags and analyzed for volatile reduced sulphur compounds using a gas chromatograph equipped with a pulsed flame photometric detector and a cryogenic trapping system. The frequency distributions of the concentrations of hydrogen sulphide (H2S), methyl mercaptan (CH3SH), dimethyl sulphide (DMS), and dimethyl disulphide (DMDS) were compared before and after the process changes. DMS was found to be the most abundant reduced sulphur compound in ambient air before the changes with an average concentration of 1.49 ppbv. After the changes, the average concentrations of CH3SH, DMS, and DMDS decreased by 28, 70, and 58%, respectively. The concentration of H2S was below its detection limit of 0.90 ppbv in most of the samples collected both before and after the process changes.