| Summary: | Lockdown or movement control order (MCO) was implemented all over the world, including Malaysia and Indonesia, during the coronavirus disease 2019 (COVID-19) pandemic. During the lockdown period, human activities were restricted. The restriction led to the reduction of human-made particulate matter released to the atmosphere. One of the indicators that could be used to estimate the concentration of particulate matter in the atmosphere is aerosol optical depth (AOD). The aim of this study is to investigate the variation in AOD level over the Malaysia and Indonesia region during this restriction period. This study has utilized monthly and daily Moderate Resolution Imaging Spectroradiometer (MODIS) Terra AOD product that can be accessed through National Aeronautics and Space Administration (NASA)'s Geospatial Interactive Online Visualization and Analysis Infrastructure (GIOVANNI) system. The developed long-Term time-Averaged map showed a high AOD level over Sumatera and South Kalimantan, with the maximum value being 0.4. The comparison among during, pre-and post-lockdown periods showed a reduction in the AOD level. The maximum AOD level decreased to 0.3 during the lockdown period compared to 0.4 in the pre-(2019) and post-lockdown periods (2021 and 2022). Average monthly time series showed no spike in the AOD level in 2020 and 2021. Hovmöller diagram showed low AOD throughout the latitude and longitude during lockdown compared to the pre-and post-lockdown periods. Analyses of the yearly AOD level showed reduction in the AOD level from +11.31% in 2019 to-18.17% and-18.01% in 2020 and 2021, respectively. The result also showed that the average daily AOD percentage during the lockdown period in 2020 had decreased to-5.34% from-3.18% in 2019 and had increased to +1.26 in 2021. © 2023 Amin A.R.M. et al., published by Sciendo.
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