Induced Impact of El Niño-Southern Oscillation and Haze Events on Aerosol Optical Depth (AOD) in the Tropical Climate of Borneo Island

Previous studies demonstrated that the El Niño–Southern Oscillation (ENSO) could modulate regional climate, thus influencing air quality in tropical latitude regions like South-east Asia. However, such influence has never been analysed in Borneo Island as it is always strongly affected by the El Niño and haze events due to the complications of the Walker and Hadley circulations that severely impact the weather in this region. To fill the gap, this study investigated aerosol concentration by aerosol optical depth (AOD) and particulate matter (PM10) in Borneo Island during the whole dynamic development of ENSO phases. The findings from this study showcased that the AOD values were usually highest in September months, mostly affecting Central Kalimantan, Indonesia, as compared to other regions in Borneo. The results suggest strong positive correlations between the aerosol optical depth (AOD) and El Niño phases, as high AOD occurred during the El Niño event. Such correlations are mainly attributed to atmospheric circulation and precipitation variation during the ENSO phase. This study further quantified the AOD variation from 2007 to 2019 attributed to changes in ENSO phases and PM10 contributions by > 50% due to anthropogenic emissions. The result also shows the importance of El Niño analysis by varying aerosol concentration (PM10) in a short-term period and a more targeted evaluation of the detected events and the specific El Niño and haze episodes.