Brown carbon (BrC) is a light-absorbing aerosol component that has a significant impact on atmospheric photochemistry and climate effects. Many studies on light absorbing characteristics of BrC (such as a fraction of water-soluble and/or water-insoluble) have been carried out in cities over the Guanzhong Basin, including radiative forcing, optical properties and sources. However, research on the Qinling Mountains is still lacking. Therefore, PM2.5 samples were collected at the northern piedmont of Qinling Mountains (QL) and Xi'an (XN) in the winter of 2020, and the optical properties and radiation effects of water extracts were analyzed and eval-uated. The mass absorption efficiency (MAE) of water-soluble organic carbon (WSOC) at 365 nm (MAE365) obtained in QL and XN were 0.18 +/- 0.03 m2 g-1 and 0.78 +/- 0.96 m2 g-1, respectively. In the ultraviolet range, the relative light absorption of WSOC relative to elemental carbon (EC) was 6.76% and 33.41% in QL and XN, respectively, and the simple forcing efficiency (SFE280-400) were 0.71 +/- 0.43 and 2.82 +/- 1.71 W g-1 in QL and XN. It may have important effects on the radiation balance of regional climate systems. The chromophores in WSOC of XN and QL are mainly composed of humic-like and protein-like substances, and humus-like substances play a dominant role in two sites (52.61% and 71.13%). Biomass combustion has a limited contribution to chromophore abundance in WSOC of QL, which is more affected by urban transmission. The fluorescence index revealed that the chromophores in WSOC had autogenous characteristics and that the organic matter was mostly newly generated. Furthermore, the molecular weight and aromatic degree in XN samples were higher than that in QL, indicating a greater capacity for light absorption. This work will be instrumental in assessing the inter-action and influence between the city and the northern piedmont of the Qinling Mountains and improve the capability of air pollution prevention and control of Guanzhong Basin.

This study presents a comprehensive analysis of organic carbon (OC), elemental carbon (EC), and particularly the light absorption characteristics of EC and water-soluble brown carbon (WS-BrC) in total suspended particles in the Kathmandu Valley from April 2013 to January 2018. The mean OC, EC, and water-soluble organic carbon (WSOC) concentrations were 34.8 +/- 27.1, 9.9 +/- 5.8, and 17.4 +/- 12.5 lig m(-3), respectively. A clear seasonal variation was observed for all carbonaceous components with higher concentrations occurring during colder months and lower concentrations in the monsoon season. The relatively low OC/EC ratio (3.6 +/- 2.0) indicates fossil fuel combustion as the primary source of carbonaceous components. The optical attenuation (ATN) at 632 nm was significantly connected with EC loading (ECs) below 15 mu g cm(-2) but ceased as ECs increased, reflecting the increased influence of the shadowing effect. The derived average mass absorption cross- of EC (MAC(EC)) (7.0 +/- 4.2 m(2) g(-1)) is comparable to that of freshly emitted EC particles, further attesting that EC was mainly produced from local sources with minimal atmospheric aging processes. Relatively intensive coating with organic aerosols and/or salts (e.g., sulfate, nitrate) was probably the reason for the slightly higher MAC(EC) during the monsoon season, whereas increased biomass burning was a major factor leading to lower MAC(EC) in other seasons. The average MAC(WS-BrC) at 365 nm was 1.4 +/- 0.3 m(2) g(-1) with minimal seasonal variations. In contrast to MAC(EC), biomass burning was the main reason for a higher MAC(WS-BrC) in the non-monsoon season. The relative light absorption contribution of WS-BrC to EC was 9.9% over the 300-700 nm wavelength range, with a slightly higher ratio (13.6%) in the pre-monsoon season. Therefore, both EC and WS-BrC should be considered in the study of optical properties and radiative forcing of carbonaceous aerosols in this region. (C) 2020 Elsevier Ltd. All rights reserved.

This study presents a comprehensive analysis of organic carbon (OC), elemental carbon (EC), and particularly the light absorption characteristics of EC and water-soluble brown carbon (WS-BrC) in total suspended particles in the Kathmandu Valley from April 2013 to January 2018. The mean OC, EC, and water-soluble organic carbon (WSOC) concentrations were 34.8 +/- 27.1, 9.9 +/- 5.8, and 17.4 +/- 12.5 lig m(-3), respectively. A clear seasonal variation was observed for all carbonaceous components with higher concentrations occurring during colder months and lower concentrations in the monsoon season. The relatively low OC/EC ratio (3.6 +/- 2.0) indicates fossil fuel combustion as the primary source of carbonaceous components. The optical attenuation (ATN) at 632 nm was significantly connected with EC loading (ECs) below 15 mu g cm(-2) but ceased as ECs increased, reflecting the increased influence of the shadowing effect. The derived average mass absorption cross- of EC (MAC(EC)) (7.0 +/- 4.2 m(2) g(-1)) is comparable to that of freshly emitted EC particles, further attesting that EC was mainly produced from local sources with minimal atmospheric aging processes. Relatively intensive coating with organic aerosols and/or salts (e.g., sulfate, nitrate) was probably the reason for the slightly higher MAC(EC) during the monsoon season, whereas increased biomass burning was a major factor leading to lower MAC(EC) in other seasons. The average MAC(WS-BrC) at 365 nm was 1.4 +/- 0.3 m(2) g(-1) with minimal seasonal variations. In contrast to MAC(EC), biomass burning was the main reason for a higher MAC(WS-BrC) in the non-monsoon season. The relative light absorption contribution of WS-BrC to EC was 9.9% over the 300-700 nm wavelength range, with a slightly higher ratio (13.6%) in the pre-monsoon season. Therefore, both EC and WS-BrC should be considered in the study of optical properties and radiative forcing of carbonaceous aerosols in this region. (C) 2020 Elsevier Ltd. All rights reserved.

Water-soluble brown carbon (BrC) plays an important role in climate change by influencing aerosol radiative forcing. There is little information on aerosol BrC over the South China Sea (SCS). In this study, water-soluble organic carbon (WSOC) in a round-year set of aerosol samples from a remote island in the northern SCS were characterized for optical properties. In-depth information about the sources and input pathways of water-soluble BrC was obtained using molecular markers and statistic tools. The highest WSOC concentrations, light absorption coefficients at 365 nm (Abs(365)) and mass absorption efficiencies at 365 nm (MAE(365)) were observed in winter when atmospheric outflow from mainland China and the northern Indo-China Peninsula prevailed. Through the year, primary emissions from biomass burning and urban secondary organic aerosols (SOA) & waste combustion, respectively, were observed to be associated with higher MAE(365) (2.47 +/- 0.40 m(2) g(-1) and 1.97 +/- 0.22 m(2) g(-1)) and to be the main contributors to Abs(365) (22.0 +/- 3.6% and 31.6 +/- 3.6%), while biogenic SOA showed little contribution. For the first time, microorganism/plankton primary emissions, mainly from the sea, was identified to be an important contributor to water-soluble BrC (13.6 +/- 4.2% of Abs(365), MAE(365): 0.98 +/- 0.30 m(2) g(-1)), especially in spring (31% of Abs(365)). This implies that emissions from microorganism/plankton warrants careful consideration in the assessment of global aerosol light absorbance.