Selection of entropy methods for determining the weightage of air pollutants in Malaysia

Air quality in Malaysia is describe in terms of Air Pollutant Index (API) which is measured based on the maximum value of sub-indices of six air pollutants (Sulphur Dioxide (SO2), Nitrogen Dioxide (NO2), Carbon Monoxide (CO), Ozone (O3), particulate matter with aerodynamic diameter less than 10 micrometres (PM10) and particulate matter with aerodynamic diameter less than 2.5 micrometres (PM2.5)). The current API cannot provide a clear image of how destructive pollution is to humans’ health because the toxicological level of these pollutants are not considered in the development of API. Thus, this study proposed an entropy method to determine the weights of air pollutants according to their hazardous level in Malaysia. This study applies four different entropy methods to weight the air pollutants which are the Hwang and Yoon method, Zeleny method, Chen and He method, and Gaussian kernel methods. Higher-weight pollutants would contribute more towards air pollution, and vice versa. This study reveals that SO2 ranks the highest with an average objective weight of 0.1914. This is followed by PM2.5, CO and PM10, NO2 and O3 with average objective weights of 0.1841, 0.1702, 0.1841, 0.1535 and 0.1324 respectively. The effect of PM2.5, and PM10 is said to be more serious since SO2 that associates with both particulate matters are difficult to breakdown and bring more harmful effects in human life as compared to the other air pollutants. Overall, Chen and He’s method proved to be the best method among the others in determining the objective weights of the air pollutants due to the smaller error values. This study signifies an enhance approach in measuring the hazardous levels of the air pollutants and the findings could be applied to improve Malaysia’s existing API for air quality monitoring.