| Strong inorganic acid mists containing sulfuric acid (H2SO 4) were identified as a "known human carcinogen" in a recent report on carcinogens by the National Toxicology Program where phosphate fertilizer manufacture was listed as one of many occupational exposures to strong acids. To properly assess the occupational exposure to H2SO4 mists in modern facilities, the objective of this study was to characterize the true H2SO4 mist concentration levels.;Three sets of experiments were conducted. Firstly, field sampling using dichotomous samplers, silica gel tubes and cascade impactors was conducted to collect the PM2.5/PM10 H2SO 4 mist concentration, total H2SO4 mist concentration, and size-resolved H2SO4 mist concentration, respectively, at phosphate fertilizer plants.;The H2SO4 concentrations were found to vary significantly among these plants with H2SO4 pump tank areas having the highest concentration level. When high aerosol mass concentrations were observed, the H2SO4 mist had its mode size in the 3.8--10 mum range that would deposit in the upper respiratory region.;Secondly, SO2 adsorption and sulfur(IV) oxidation were investigated under various sampling times, SO2 concentrations and sampling flowrates. Experimental results verified that the collecting medium can adsorb SO 2 gas and the extraction procedure of NIOSH Method 7903 aids the transformation of SO2 into sulfate to cause a positive artifact. The experimental data were also fitted into a deactivation model for estimating the artifact sulfate concentration.;Thirdly, a honeycomb denuder system and the deactivation model were applied to minimize the artifact sulfate of NIOSH Method 7903 in a field sampling campaign. Both the system and the model were shown to effectively reduce the artifact sulfate concentration. However, the concentration thus determined was still higher than that measured by a cascade impactor which had no artifact. One possible reason is the residual sulfate in the collecting medium. |
