A training session of air dispersion modeling inviting officials from 3 counterpart agencies, namely Department of Industrial Works (DIW), Industrial Estate Authority of Thailand (IEAT) of Ministry of Industry (MOI) and Pollution Control Department (PCD) of Ministry of Natural Resources and Environment (MNRE) was held on 18 November 2020. 21 participants from the agencies including 4 from 3 industrial estate offices joined the session.
Purposes of the session were to share results of air dispersion modeling using PRTR data reported by individual factories and refined through an interview survey including comparison between the results and data of ambient air monitoring conducted by PCD and to discuss further improvement of modeling.
METI-LIS (*) was used as an air dispersion model to calculate annual ambient concentration of 6 objective substances, namely Benzene, Acrylonitrile, 1,3-Butadiene, Styrene, Vinyl Chloride, and 1,2-Dichlorethylene in Map Ta Phut (MTP) and IRPC areas in 2014, 2015 and 2016.
For details on results of air dispersion modeling, please see the attached presentation file excluding confidential information such as individual PRTR data or concentration maps calculated by METI-LIS, etc.
The results showed relatively good relation between air monitoring data and calculated data by METI-LIS for Acrylonitrile in 2016 and Vinyl Chloride in MTP, and Benzene, Acrylonitrile, 1,3-Butadiene, and Styrene in IRPC excepting when very high concentration was monitored in a month. The other estimated results in MTP than the ones mentioned above were very low-level concentration comparing with monitoring data.
Then, the following potential reasons of gaps between air monitoring data and estimated data were discussed:
- There may be missing PRTR report from some factories,
- Lower emissions may have been reported for PRTR from factories than the actual,
- High concentration monitoring data may not be reflected to calculated data, because calculated data represent annual average concentration using daily-averaged emission, and,
- Emissions from mobile sources or any other non-point sources (NPSs) such as gas station, small-medium sized enterprises (SMEs), etc. were not accounted for Benzene.
Based on the results and discussions at the training session, recommendations to fill in the potential gaps above are summarized as follows:
- Reported PRTR data should be carefully examined by authorities,
- The emission situation (shut-down or turn-around of the process) at the day when very high concentrations were monitored should be grasped, and
- Application of more advanced model with development of methods to estimate and allocate total emission amount from NPSs to that in specified target areas would be a next stage for further improvement of modeling while background level of Benzene may be assumed as 0.5 – 1.0 micro-g/m3 according to estimated results in the IRPC area.
(*) A Gaussian dispersion model developed by Ministry of Economy, Trade and Industry (METI) of Japan. For more details, please see the website of METI-LIS at https://www.aist-riss.jp/projects/METI-LIS/download.htm.