Measurement report: Long-emission-wavelength chromophores dominate the light absorption of brown carbon in aerosols over Bangkok: impact from biomass burning

Abstract

Abstract. Chromophores represent an important portion of light-absorbing species, i.e., brown carbon. Yet knowledge of what and how chromophores contribute to aerosol light absorption is still sparse. To address this problem, we examined soluble independent chromophores in a set of year-round aerosol samples from Bangkok. The water-soluble fluorescent chromophores identified via excitation–emission matrix (EEM) spectroscopy and follow-up parallel factor analysis could be mainly assigned as humic-like substances and protein-like substances, which differed in their EEM pattern from that of the methanol-soluble fraction. The emission wavelength of fluorescent chromophores in environmental samples tended to increase compared with that of the primary combustion emission, which could be attributed to secondary formation or the aging process. Fluorescent indices inferred that these light-absorbing chromophores were not significantly humified and comprised a mixture of organic matter of terrestrial and microbial origin, which exhibited a different characteristic from primary biomass burning and coal-combustion results. A multiple linear regression analysis revealed that larger fluorescent chromophores that were oxygen-rich and highly aromatic with high molecular weights were the key contributors of light absorption, preferably at longer emission wavelengths (λmax⁡ > 500 nm). Positive matrix factorization analysis further suggested that up to 50 % of these responsible chromophores originated from biomass burning emissions.

The Sources, Molecular Compositions, and Light Absorption Properties of Water‐Soluble Organic Carbon in Marine Aerosols From South China Sea to the Eastern Indian Ocean

“…Based on this simplistic bleaching model, the MAE 365 values of WSOC were 1.22 ± 0.86 and 1.32 ± 0.73 m 2 / gC for South and Southeast Asian source regions, respectively, which are within the range of those reported in pollution source regions in South, Southeast, and East Asia (Cheng et al, 2016;Geng et al, 2020;Kirillova et al, Kirillova Andersson,Tiwari et al, 2014Mo et al, 2021Tang et al, 2021;Yan et al, 2015).…”

Molecular Signatures and Sources of Fluorescent Components in Atmospheric Organic Matter in South China

“…The combination of excitation–emission matrix (EEM) spectroscopy and parallel factor analysis (PARAFAC) is broadly used in identifying the sources, structural information, and optical properties of chromophores in aquatic dissolved organic matter (DOM). − Recently, EEM-PARAFAC has been extended and applied to investigations of atmospheric soluble brown carbon (BrC). − However, the identification and chemical interpretation of PARAFAC-derived fluorescent components (FCs) is largely based on the knowledge of aquatic DOM. Studies have suggested that the sources and chemical composisiton of atmospheric organic matter (AOM) differ from those of aquatic DOM, ,, which may therefore lead to misinterpretations of the PARAFAC-derived FCs.…”

Technical note: Identification of chemical composition and source of fluorescent components in atmospheric water-soluble brown carbon by excitation-emission matrix with parallel factor analysis: Potential limitation and application

“…The higher content of C3 in WSOM in the dry season suggested the occurrence of more highly aromatic and highly oxidized compounds. These results could be explained by the fact that more aged organic aerosols and dust were transported from the northern region of China (Jiang et al, 2021). In contrast, the slightly higher C2 content in the wet season may be attributed to the relatively stronger secondary formation of bio-SOAs and photodegradation effects in high-temperature and relative humidity season.…”