Spatio-temporal analysis of aerosol optical depth using rotated empirical orthogonal function over the Maritime Continent from 2001 to 2020

Abstract

The deterioration in the annual air quality of the Maritime Continent (MC) is mainly caused by biomass burning haze (BBH) and the surrounding atmospheric conditions. This study aims to investigate the spatial and temporal variations of the aerosol optical depth (AOD) and its relationship with biomass burning and climate anomaly factors in the MC from 2001 to 2020. Using aerosol model reanalysis products from the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2), values of the aerosol optical depth (AOD) over the MC were collected and processed to obtain a better understanding of the characteristics of the aerosol loading over the MC. Using the varimax rotated empirical orthogonal function (REOF) approach, we assess the spatio-temporal distributions of the AOD over the MC from 2001 to 2020. The REOF maximized the variances explained for the primary modes and has shown clearer relationship between the spatiotemporal patterns of identified modes. The first three REOF modes of the AOD accounted for a total variance of 73.7%. The first mode (REOF1) explaining 35.8% is the main mode that represent fire burning that concentrated over the 0° latitude. REOF1 represents the emission from burning activities which primarily occurred in the Kalimantan and Sumatra based on their correlation with the total hotspots, which reach 0.73, which a certain extent of correlation with the climate anomalies, including El Niño, positive DM, and their coincidence. The second (REOF2) also explaining 35.8% represents the AOD distribution influenced by the biomass burning emission transported from the Indochina in the area to the north of 5°N which has an opposite mode with the general mode in MC except for Java area. Meanwhile, PC3 AOD has reduced to 2.2% in the rotation process and represent the influence of monsoon movement on the AOD level. In short, the study highlights spatial and temporal AOD distribution and the phenomena of burning mass and climate indices in the long-term MERRA reanalysis dataset to allow more understanding of the causal links of AOD in MC to the climate features.