modified . The accuracy of ANN-based models is also heavily reliant on data . Many algorithms require the input of large amounts of data before they can output useful and accurate results .
In the context of air quality monitoring and leak detection , it is not always possible to obtain realworld data , especially if the associated material is unsafe for human health and the environment . Hence , many researchers have turned to numerical methods to generate quantitative data to train and test ML models . Computational fluid dynamics ( CFD ) is one such numerical method that has gained prominence due to its reliability and robustness as an engineering tool . CFD models have been utilised to study pollution and toxic gas dispersion in a variety of scenarios and areas , with an example given in Figure 3 . Through solving governing equations of fluid flow dynamics , the tool has provided additional insights into the flow of pollutants and toxic gases , making it useful for the study of air quality and the development of leak detection systems . In the past , CFD models were not conventionally used as they were time-consuming and required a large number of computational resources . However , advancements in computation hardware have allowed the integration of CFD into different kinds of studies . The models developed using CFD can be tuned to reproduce specific scenarios via measured meteorological and process parameters such as wind speed , wind direction , temperature , and pressure . Moreover , models validated using experimental data can be employed to simulate additional conditions and scenarios that experiments cannot achieve due to the possible risks , thereby providing additional datasets for training purposes . The integration of CFD and ANN models can be used for a variety of purposes . A few examples are described below .
Illegal Plastic Burning
Since China ’ s ban on plastic waste imports in 2018 , countries in Southeast Asia have become the top alternatives for waste trafficking by developed countries such as the US , the UK , and Japan . In that same year , Malaysia became the largest importer of plastic waste , importing over 850,000 metric tons of plastic waste , many
Figure
3 : The dispersion of ( a ) benzene and ( b ) methane across a residential area in Jenjarom , Kuala Langat as simulated by Yu et al . ( 2022 ) using CFD .
of which ended up in landfills or burned in illegal factories . The burning of plastics results in the release of pollutants such as dioxins , furans , mercury , and polychlorinated biphenyls ( PCBs ) into the atmosphere .
Residents in Jenjarom , Kuala Langat , Malaysia had to suffer through the toxic clouds generated by such illegal burning factories until the Government intervened and shut them down . However , there are still illegal factories that are burning waste secretly . The CFD-ANN model developed by Yu et al . ( 2022 ) was found to be able to predict the illegal burning location with just eight sensors placed around the city . The ANN model was able to learn how gas dispersion and mixing effect change , depending on the different burning locations , wind speeds , and wind directions . After training , the ANN was able to predict other source locations without requiring further time-consuming simulations via CFD .
29