| dc.description.abstract | Hazardous Air Pollutants (HAPs) are closely associated with public health issue, which has received much attention in recent years. In 2021, Taiwan EPA announced the Emission Standards for Hazardous Air Pollutants from Stationary Pollution to control 22 HAPs as the first stage. In order to obtain average concentrations over a relative long period of time for these target HAPs, a diffusive sampling technique similar to the U.S. EPA Method 325A/B method was developed. To calculate sample concentrations diffusive uptake rates are required for individual target compounds. For sample analysis a thermal desorption (TD) technique for preconcentration coupled with gas chromatography mass spectrometry (GC-MS) was employed.
In this research, we use both Carbopack X and Carboxen 569 sampling tubes. The uptake rates of the 22 target compounds including 1,3-butadiene and vinyl chloride which are not covered by the U.S. EPA Method 325A/B were determined in this study in a self-built exposure chamber. We found that the uptake rates were in high agreement with those determined by the U.S. EPA Method 325B using Carbopack X based on two repeated results, and the uptake rates were between -4% to 13% for Carbopack X and -13% to 7% for Carboxen 569.
Both types of sorbents were tested for optimized conditions for the 22 HAPs from the perspectives of correlation coefficients (R2) and method detection limits (MDL), as well as other relevant factors in diffusive sampling, such as the effect of humidity, back diffusion, tolerance to high ambient concentration variability, etc. Our results show that Carbopack X can be used to sample 55 HAPs including 1, 3-butadiene, with R2 ranging from 0.993 to 1.000 and MDL ranging from 0.11 to 0.97 ppbv. The relative standard deviations (RSD) in uptake rates are all lower than 20%, between 4% and 17%. The recoveries are between 91% and 116%. On the other hand, Carboxen 569 can detect 44 HAPs including vinyl chloride, with R2 ranging from 0.990 to 1.000 and MDL ranging from 0.47 to 0.95 ppbv. The RSD of uptake rates are between 5% to 19%, and the recoveries are between 87% and 117%.
After completion of laboratory assessment, one-week field measurement was conducted from November 12, 2020 to November 19, 2020. The field measurement of diffusive sampling showed comparable results to TD-GC/MS measurements by averaging hourly data from online TD-GC/MS. For instance, benzene was detected as 0.31 ppbv and 0.27 ppbv for diffusive sampling and on-line method, respectively. Toluene and ethylbenzene were measured as 6.13 ppbv vs. 5.37 ppbv, and 0.26 ppbv vs. 0.24 ppbv, respectively. This diffusive sampling method not only can make sample deployment with ease, but also provide concentration estimates for target HAPs over a relatively long time period of more than 2 weeks. | en_US |