[Design, construction and performance of chromium mist generator]

ABSTRACT

The chromium mist generator is an essential tool for research and for making evidence-based recommendations in evaluating air pollution and its control systems. The purpose of this study was to design and construct a homogeneous chromium mist generator and to look at the effects of factors such as sampling height and distance between samplers in side-by-side sampling on the chromium mist sampling method. First we developed a mist generator, using a chromium electroplating bath in pilot scale. Concentrations of CrO3 and sulfuric acid in plating solution were 125 g L-1 and 1.25 g L-1, respectively. To set up permanent air sampling locations, a Plexiglas cylindrical chamber [75 cm height, 55 cm i.d] was installed as the bath overhead. Sixty holes were made on the chamber in 3 rows [20 in each row]. The distance between rows and holes was 15 and 7.5 cm, respectively. Homogeneity and the related factors were studied using a side-by-side air sampling method. Forty-eight clusters of samples were collected on polyvinyl chloride [PVC] filters contained in sampling closed-face cassettes. Cassettes were located 35, 50, and 65 cm above the solution surface with < 7.5 and/or 7.5-15 cm distance between heads. All samples were analyzed by the NIOSH method 7600. ANOVA tests showed no significant differences between locations in side-by-side sampling [P=0.82] or between different sampling heights or sampler distances [P=0.86 and 0.86, respectively]. However, there were notable differences between means of coefficients of variation [CV] in various heights and distances. We conclude that the most chromium mist homogeneity could be obtained at a height of 50 cm from the bath solution surface and with a distance of < 7.5 cm between samplers