Emission of water soluble brown carbon from different combustion sources: optical properties and functional group characterisation

Abstract

Abstract Brown carbon (BrC) has a large impact on the Earth’s radiative balance. This study examined BrC’s optical characteristics, chemical functional groups, and total organic carbon (TOC) in deposited particulate matter from combustion of biomass, fossil fuels, and mosquito coil. A UV–vis spectrophotometer was used to assess BrC’s optical properties, a TOC analyzer was used to quantify TOC, and attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR) was used to identify functional group. The light absorption properties (absorption coefficient (babs-BrC), mass absorption efficiency (MAE365), absorption angstrom exponent (AAE), and refractive index (kabs-BrC)) were determined. Among biomasses, wheat straw exhibited the greatest value of babs-BrC (27.26 × 103 ± 4.09 × 103 Mm−1) whereas maize straw had the lowest value of babs-BrC (7.38 × 103 ± 1.11 × 103 Mm−1). A higher light absorption coefficient at 365 nm suggested that chromophores contributed more to the process. AAE followed this sequence - mosquito coil (5.46 ± 0.82) > biomass (5.13 ± 1.45) > fossil fuels (2.85 ± 0.32). The highest value of MAE365 (0.99 ± 0.15 m2 gC−1) and kabs-BrC (0.028 ± 0.004) was obtained in wheat straw, whereas the lowest value of MAE365 (0.07 ± 0.011 m2 gC−1) and kabs-BrC (0.002) was identified in octane. Biomasses samples showed a strong peak at ∼850, ∼1368, ∼1370, ∼1306, and near 1640 cm−1, indicating that the major component of BrC was organic nitrate R-ONO2 which is responsible to increase the light absorption properties. It also contains complex heterocyclic aromatic ring compounds, carbonyl group (C=O), and nitrogen-containing groups such as −NO 2, C≡N. The projected substantial contribution of BrC to overall light absorption is one illustration of the probable climatic effect of biomasses and fossil fuel burning in Southeast Asian region.