The secondary formation of BrC was dominated by anthropogenic and biogenic emissions as well as atmospheric multiphase reactions (Hems et al., 2021 Ni et al., 2021 Qin et al., 2018). In terms of primary emission, biomass burning and fossil fuel combustion as well as vehicle exhaust were found to be the dominant sources of BrC (Xie et al., 2019a). In general, BrC in the atmosphere comes from a variety of primary emission sources and secondary formation processes. The observed effects of BrC deposition on the environment and human health cannot be ignored. Furthermore, it has been proved that BrC could indirectly induce harmful outcomes to human health by impeding the aging and photocatalytic degradation of persistent organic pollutants and heavy metals (Yan et al., 2018). On the global scale, BrC could account for about 40% of total aerosol absorption in the 300-400 nm wavelength range (Jo et al., 2016), twice the percentage at 550 nm (Chung et al., 2012). In the ultraviolet to visible spectral range, the wavelength dependence of BrC absorption decreases with increasing wavelength, particularly at short wavelengths, and is more pronounced than that of BC (Huang et al., 2018 Huang et al., 2020). Growing evidence suggests that the solar radiation absorption of atmospheric particles by such as BC and BrC significantly reduced photolysis rates, and in turn indirectly affected the photochemical process (Huang et al., 2020 Jo et al., 2016 Wu et al., 2020). ![]() On account of its large abundance and strong light absorption in the near-UV spectrum, BrC shows important environmental significance in terms of atmospheric radiation balance and the global climate (Zhang et al., 2017a). BrC can absorb radiation from the near-ultraviolet (UV) to visible wavelengths and even shows absorption similar to BC. These light-absorbing components of OC were defined as brown carbon (BrC) (Hettiyadura et al., 2021 Zhang et al., 2020b). Despite OC being commonly treated purely as an effective light-scattering species (Koch et al., 2009 Laskin et al., 2015), recent research observed that certain parts of OC have light-absorbing characteristics with colors ranging from brown to yellow, which could significantly induce positive climate forcing at regional and even global scales (Pokhrel et al., 2017 Saleh et al., 2013 Saleh et al., 2014). BC can impact global climate by absorbing solar radiation directly (He et al., 2014 Jacobson, 2001 Koch et al., 2009). non-heating seasons and that the properties of WS-BrC significantly depended on primary emissions (e.g., combustion emissions) and secondary formation.Ĭarbonaceous aerosols, including organic carbon (OC) and black carbon (BC), are vital components of atmospheric aerosol (Liu et al., 2022 Zhou et al., 2016). The results of source apportionment suggested that the potential source regions of WS-BrC varied in heating vs. By combining fluorescence excitation-emission matrix (EEM) spectra with the parallel factor (PARAFAC) model, humic-like (C1 and C2) and protein-like (C3) substances were identified, and accounted for 61.40%±4.66% and 38.6%☓.78% at Baotou, and 60.33%☖.29% and 39.67%±4.17% at Wuhai, respectively. Comparatively, the levels of WS-BrC in developing regions (such as cities in Asia) were higher than those in developed regions (such as cities in Europe and Australia), indicating the significant differences in energy consumption in these regions. ![]() This study showed that the annual average abundances of Water-soluble BrC (WS-BrC) were 9.33☗.42 and 8.69☖.29 µg/m 3 in Baotou and Wuhai and the concentrations, absorption coefficient (Abs 365), and mass absorption efficiency (MAE 365) of WS-BrC presented significant seasonal patterns, with high values in the heating season and low values in the non-heating season while showing opposite seasonal trends for the Absorption Ångström exponent (AAE 300-400). However, the understanding of the chemical and optical properties of BrC is limited, especially in some resource-dependent cities with long heating periods in northwest China. As a vital type of light-absorbing aerosol, brown carbon (BrC) presents inherent associations with atmospheric photochemistry and climate change.
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