Brown carbon light absorption over an urban environment in northern peninsular Southeast Asia

Shantanu Kumar Pani; Neng-Huei Lin; Stephen M Griffith; Somporn Chantara; Chung-Te Lee; Duangduean Thepnuan; Ying I Tsai

doi:10.1016/j.envpol.2021.116735

Brown carbon light absorption over an urban environment in northern peninsular Southeast Asia

Environ Pollut. 2021 May 1:276:116735. doi: 10.1016/j.envpol.2021.116735. Epub 2021 Feb 11.

Authors

Shantanu Kumar Pani¹, Neng-Huei Lin², Stephen M Griffith¹, Somporn Chantara³, Chung-Te Lee⁴, Duangduean Thepnuan⁵, Ying I Tsai⁶

Affiliations

¹ Department of Atmospheric Sciences, National Central University, Taoyuan, 32001, Taiwan.
² Department of Atmospheric Sciences, National Central University, Taoyuan, 32001, Taiwan; Center for Environmental Monitoring and Technology, National Central University, Taoyuan, 32001, Taiwan. Electronic address: nhlin@cc.ncu.edu.tw.
³ Environmental Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand; Environmental Chemistry Research Laboratory, Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand.
⁴ Graduate Institute of Environmental Engineering, National Central University, Taoyuan, 32001, Taiwan.
⁵ Environmental Chemistry Research Laboratory, Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand.
⁶ Department of Environmental Engineering and Science, Chia Nan University of Pharmacy and Science, Tainan, 71710, Taiwan.

PMID: 33611195
DOI: 10.1016/j.envpol.2021.116735

Abstract

Light-absorbing organic carbon (or brown carbon, BrC) has been recognized as a critical driver in regional-to-global climate change on account of its significant contribution to light absorption. BrC sources vary from primary combustion processes (burning of biomass, biofuel, and fossil fuel) to secondary formation in the atmosphere. This paper investigated the light-absorbing properties of BrC such as site-specific mass absorption cross-section (MAC_BrC), absorption Ångström exponent (AAE_BrC), and the absorbing component of the refractive index (k_BrC) by using light absorption measurements from a 7-wavelength aethalometer over an urban environment of Chiang Mai, Thailand in northern peninsular Southeast Asia (PSEA), from March to April 2016. The contribution of BrC to total aerosol absorption (mean ± SD) was 46 ± 9%, 29 ± 7%, 24 ± 6%, 20 ± 4%, and 15 ± 3% at 370, 470, 520, 590, and 660 nm, respectively, highlighting the significant influence of BrC absorption on the radiative imbalance over northern PSEA. Strong and significant associations between BrC light absorption and biomass-burning (BB) organic tracers highlighted the influence of primary BB emissions. The median MAC_BrC and k_BrC values at 370 nm were 2.4 m² g^-1 and 0.12, respectively. The fractional contribution of solar radiation absorbed by BrC relative to BC (mean ± SD) in the 370-950 nm range was estimated to be 34 ± 7%, which can significantly influence the regional radiation budget and consequently atmospheric photochemistry. This study provides valuable information to understand BrC absorption over northern PSEA and can be used in model simulations to reassess the regional climatic impact with greater accuracy.

Keywords: Absorption Ångström exponent; Biomass burning; Chiang Mai; Imaginary part of refractive index; Mass absorption cross-section.

MeSH terms

Aerosols / analysis
Air Pollutants* / analysis
Asia, Southeastern
Biomass
Carbon* / analysis
Environmental Monitoring
Thailand

Substances

Aerosols
Air Pollutants
Carbon