| 英文摘要 |
This project is aimed at monitoring selected volatile organic compounds (VOCs) in ambient air which are included in the list of hazardous air pollutants (HAPs) announced by Taiwan EPA. These 22 target HAPs include acetone, 1,1-dichloroethane, 1,2-dichloroethane, vinyl chloride, 1,3-butadiene, benzene, toluene, xylene, trichloroethane, trichloroethylene, tetrachloroethylene, 1,2-dichloropropane, carbon tetrachloride, styrene, ethylbenzene, 1,1-dichloroethylene, 1,1,2-trichloroethane, allyl chloride, dichlorobenzene and accompanying isomers. An on-site on-line method based on thermal desorption gas chromatography mass spectrometry (TD-GC/MS) was developed and tested for the target HAPs with hourly data resolution. This on-line method is mainly based on the existing NIEA A715.15B method in terms of quality control/assurance including concentration calibration, as well as the assessment of accuracy, precision and limits of detection (LOD).
With the GC/MS both modes of total ion counting (TIC) and selected ion monitoring (SIM) were used for measuring target compounds. The results of calibration show that the relative standard deviations (RSD) range from 3.85 to 23.98% and 3.91 and 19.58% for TIC and SIM, respectively. The linearity (R2) ranges 0.982~0.999 and 0.988~0.999 for TIC and SIM, respectively. The LODs range 0.11~1.76ppb and 0.08~0.36ppb for TIC and SIM, respectively. The recovery is between 85.58~116.99% and 0.62~4.56% for TIC and SIM, respectively.
After the completion of laboratory QA assessment, a month-long (34 days) on-site measurement was conducted from October 5, 2019 to November 7, 2019. Other than few interruptions due to ion source cleaning, air conditioner repair, calibration runs, etc., resulting in the loss of 144 hours of data, the field monitoring led to the detection of 6 out of 22 target compounds, i.e., vinyl chloride, acetone, carbon tetrachloride, benzene, toluene and 1, 2-dichloroethane. Of those 6 detected compounds acetone and toluene were the most frequently detected species. The average concentration of acetone during the monitoring period was 2.36 ppb and the maximum concentration was 25.26 ppb; the average concentration of toluene was 0.38 ppb and the highest value was 5.84 ppb. Other less frequently detected compounds include 2-butanone, dichloromethane, chloroform and methyl acetate. Except for methyl acetate due to the lack of standard, the other three species were able to be quantified. The average and maximum concentrations are 0.26 and ppb 3.17 ppb for 2-butanone, respectively; 0.55 and 3.63 ppb for dichloromethane, respectively; and 0.08 and 2.12 ppb for chloroform, respectively.
In order for the TD-GC/MS method to be successfully implemented for future field measurements, the project has established the suggested specifications of QA/QC protocol. The in-lab calibration before field measurements is the same as that specified in NIEA A715.15B. However, in order to maximize data availability, it is suggested that: 1. the recovery requirement can be relaxed from 70~130% to 60~140%, 2. the ion source cleaning needs to be performed every 2-3 weeks, depending on the instrument used, and a new multipoint calibration should follow after that.
As the second part of the project, the establishment of the diffusive sampling method for the target HAPs is based on the published methods of U.S.EPA, ASTM, ISO and other relevant studies found in the journal papers such as Atmospheric Environment and Science of the Total Environment. Due to the differences in diffusive properties in absorptive materials, the uptake rate is compound dependent and needs to be determined for individual compounds beforehand prior to field sampling which is scheduled to be completed by mid-2020. Both Carbopack X and carboxen 569 have been chosen as the tube sorbents for diffusive sampling after literature search and screening. The major instrument used in this study is an automated TD-GC/MS in TIC mode.
The project has successfully completed both in-laboratory preparation and a field campaign for the on-line TD-GC/MS method. The diffusive sampling method is also under intensive preparation. Further optimization of the analytical systems and field measurements will be carried out in 2010 in selected industrial areas to refine both methods by including more industrial types and thus detected compounds.
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