This study was designed to evaluate the effects of temperature and humidity on the sampling efficiency of mixed organic vapors of 1,2-DCE, benzene, and MIBK by 3 different types of diffusion monitors.
Independent variables used for the study were temperatures (25oC, 35oC), humidifies (30%, 80%), and vapor concentrations (low, medium, and high). In addition, vapor concentrations measured by the traditional charcoal tube method were used as reference values and were compared with those of by diffusion monitors.
The results were as follows:
1. The desorption efficiencies(DE) of 1,2-DCE and benzene from charcoal tubes and from diffusion monitors ranged from 98% to 105%. In contrast, the DEs of MIBK from charcoal tubes and diffusion monitors except DM1 ranged from 71% to 85%. The DE of MIBK from DM1 was 98%.
2. No statistically significant differences of 1,2-DCE concentrations and the sampling efficiencies regardless of temperatures and humidifies studied between charcoal tube and 3 diffusion monitors were found.
3. At 80% humidity, increasing frequencies of 1,2-DCE breakthrough at higher temperature and higher vapor concentration measured by charcoal tubes were observed.
4. No statistically significant difference of benzene concentrations were found between charcoal tube and diffusion monitors except DM3. The sampling efficiencies of DM3 were statistically significantly lower at all experimental conditions except the 35oC and 30% humidity condition.
5. No statistically significant difference of MIBK concentrations were found between charcoal tube and diffusion monitors except DM3. The sapling efficiencies of DM3 were statistically significantly higher at hasher humidity conditions regardless of temperature. Although statistically not significant, sampling efficiency of MIBK showed positive correlation with humidity while negative correlation with concentration was observed.
6. For sampling 1,2-DCE and benzene, no significant variations of concentrations among three diffusion monitors regardless of temperature and humidity conditions were found. For MIBK sampling, however, wide variations with increasing humidity among diffusion monitors were obtained.
In conclusion, this study suggests that diffusion monitors will be a reasonable substitute for the traditional charcoal tubes for sampling non-polar organic vapors at temperature and humidity conditions studied. For polar organic vapors, use of an alternative desorption solution other than CS2 is recommended because of its low desorption efficiency. In addition, since variable resorts among diffusion monitors for polar organic vapors particularly at higher humidity conditions were observed, further study is recommended of the effects of humidity on the performance of diffusion monitors.
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