The characteristics of atmospheric brown carbon in Xi'an, inland China: sources, size distributions and optical properties

Abstract

<p><strong>Abstract.</strong> To investigate the characteristic of atmospheric brown carbon (BrC) in the semi-arid region of East Asia, PM<sub>2.5</sub> and size-resolved particles in the urban atmosphere of Xi'an, inland China during the winter and summer of 2017 were collected and analyzed for optical properties and chemical compositions. Methanol extracts (MeOH-extracts) were more light-absorbing than water extracts (H<sub>2</sub>O- extracts) in the optical wavelength of 300–600 nm, and well correlated with nitrophenols, polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (R<sup>2</sup> > 0.6). The light absorptions (abs<sub>λ=365nm</sub>) of H<sub>2</sub>O- extracts and MeOH-extracts in winter were 28 ± 16 M/m and 49 ± 32 M/m, respectively, which are about 10 times higher than those in summer, mainly due to the enhanced emissions from biomass burning for house heating. Water extracted BrC predominately occurred in the fine mode (< 2.1 µm) during winter and summer, accounting for 81 % and 65 % of the total absorption of BrC, respectively. The light absorption and stable carbon isotope composition measurements showed an increasing ratio of abs<sub>λ=365nm</sub>-MeOH to abs<sub>λ=550nm</sub>-EC along with an enrichment of <sup>13</sup>C in PM<sub>2.5</sub> during the haze development, indicating an accumulation of secondarily formed BrC (e.g., nitrophenols) in aerosol aging process. PMF analysis showed that biomass burning, fossil fuel combustion, secondary formation, and, fugitive dust are the major sources of BrC in the city, accounting for 54.7 %, 19 %, 16.2 %, and 10 % of the total BrC, respectively.</p>

Continuous Measurement and Molecular Compositions of Atmospheric Water‐Soluble Brown Carbon in the Nearshore Marine Boundary Layer of Northern China: Secondary Formation and Influencing Factors

“…Contributions of primary emissions to BrC have been widely reported in Beijing (Du et al, 2014a;Yan et al, 2015Yan et al, , 2017 and Xi'an (R. J. Wu et al, 2019) in northern China, Thailand and Indo-Gangetic Plain in South Asia (Satish et al, 2017;Srinivas & Sarin, 2014;Tang et al, 2021), the Tibetan Plateau (Y. Wang, Hu, et al, 2019), Los Angeles Basin (X.…”