Characterizing Aerosol Size Distributions, Fine Mode Aerosol Dominance, and Seasonal Aerosol Regimes over Penang, Malaysia Using AERONET SDA Retrievals.
Atmospheric aerosol size distributions play a critical role in determining aerosol radiative effects, air quality, and climate interactions. This study investigates aerosol size characteristics over Penang, Malaysia, using AERONET Version 3 Spectral Deconvolution Algorithm (SDA) Level 2.0 observations collected between 2018 and 2022. The analysis focused on Aerosol Optical Depth (AOD), Fine Mode Fraction (FMF, η), and Ångström Exponent (AE) to characterize temporal variability and aerosol regimes in a tropical coastal environment. Descriptive statistics showed mean values of 0.284 ± 0.210 for AOD, 0.713 ± 0.145 for FMF, and 1.251 ± 0.212 for AE, indicating persistent dominance of fine-mode aerosols. Monthly analysis revealed elevated aerosol loading during March–April and September, while AE and FMF remained consistently high throughout the year. Interannual distributions demonstrated relatively stable aerosol size characteristics during the study period, with median AE and FMF values remaining above 1.2 and 0.70, respectively. Aerosol regime classification indicated that mixed aerosols (47.89%) and fine-mode-dominated aerosols (45.05%) were the most frequently observed conditions, whereas coarse-mode aerosols accounted for only 7.05% of observations. A positive relationship between AE and FMF (R² = 0.421) confirmed the strong influence of fine particles on aerosol optical properties. Seasonal analyses further revealed enhanced fine-particle dominance during the inter-monsoon and Southwest Monsoon periods, while marine influences were more evident during the Northeast Monsoon. The findings demonstrate that aerosol characteristics over Penang are predominantly controlled by fine-mode particles originating from anthropogenic activities, secondary aerosol formation, and regional biomass-burning transport, providing valuable insight into aerosol variability within the Maritime Continent region..
Key Words– Aerosol Optical Depth, Fine Mode Fraction, Ångström Exponent, Aerosol Regimes, Southeast Asia.
