Columnar aerosol types and compositions over peninsular Southeast Asia based on long-term AERONET data

Sheng-Hsiang Wang,Neng-Huei Lin,Hsiang-Yu Huang,Somporn Chantara,Chung-Te Lee,Brent N Holben,Che-Hsuan Lin,Serm Janjai,Shantanu Kumar Pani

doi:10.1007/s11869-021-01119-2

Sheng-Hsiang Wang, Neng-Huei Lin + Show 7 more

Open Access

https://doi.org/10.1007/s11869-021-01119-2

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Abstract

AbstractAerosol chemical components such as black carbon (BC) and brown carbon (BrC) regulate aerosol optical properties, which in turn drive the atmospheric radiative forcing estimations due to aerosols. In this study, we used the long-term measurements from AERONET (Aerosol Robotic Network) to better understand the aerosol types and composition with respect to their seasonal and spatial variabilities in peninsular Southeast Asia (PSEA, here defined as Vietnam, Cambodia, Thailand, Laos, and Myanmar). Two methods (i.e., aerosol type cluster and aerosol component retrieval) were applied to determine the aerosol type and chemical composition during the biomass-burning (BB) season. AERONET sites in northern PSEA showed a higher AOD (aerosol optical depth) compared to that of southern PSEA. Differences in land use pattern, geographic location, and weather regime caused much of the aerosol variability over PSEA. Lower single-scattering albedo (SSA) and higher fine-mode fraction (FMF) values were observed in February and March, suggesting the predominance of BB type aerosols with finer and stronger absorbing particles during the dry season. However, we also found that the peak BB month (i.e., March) in northern PSEA may not coincide with the lowest SSA once dust particles have mixed with the other aerosols. Furthermore, we investigated two severe BB events in March of 2014 and 2015, revealing a significant BrC fraction during BB event days. On high AOD days, although the BC fraction was high, the BrC fraction remained low due to lack of aerosol aging. This study highlights the dominance of carbonaceous aerosols in the PSEA atmosphere during the BB season, while also revealing that transported dust particles and BrC aerosol aging may introduce uncertainties into the aerosol radiative forcing calculation.

Highlights

Atmospheric aerosols, either from natural sources or anthropogenic emissions, perturb Earth’s radiation budget directly by scattering and absorbing incoming solar radiation (Charlson et al 1992; Chylek and Wong 1995; Hassan et al 2015)
We investigated the aerosol type and optical properties in terms of seasonal to spatial variabilities over peninsular Southeast Asia (PSEA) based on the long-term measurements from 6 sun photometer AERONET (Aerosol Robotic Network) sites
AERONET sites in northern PSEA show a higher aerosol optical depth (AOD) compared to southern PSEA, where the different weather regimes and land use activities drive the regional variability of aerosol in the dry season (February to April)

Summary

Introduction

Atmospheric aerosols, either from natural sources or anthropogenic emissions, perturb Earth’s radiation budget directly by scattering and absorbing incoming solar radiation (Charlson et al 1992; Chylek and Wong 1995; Hassan et al 2015). Aerosol direct radiative forcing is usually negative at the top of the atmosphere (TOA) under clear sky conditions. It can become less negative or even positive with an increase in aerosol absorption, especially over high albedo surfaces (Boucher et al 2013; Feng et al 2013; Wang et al 2007). This aerosol absorption is mainly regulated by the aerosol chemical components and their respective mass fractions. It is essential to gain a better understanding of aerosol chemical composition based on observational studies to reduce these uncertainties (e.g., Van Beelen et al 2014)

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