Carbonaceous aerosols have great influence on the air quality, human health and climate change. Except for organic carbon (OC) and elemental carbon (EC), brown carbon (BrC) mainly originates from biomass burning as a group of OC, with strong absorption from the visible to near-ultraviolet wavelengths, and makes a considerable contribution to global warming. Large numbers of studies have reported long-term observation of OC and EC concentrations throughout the world, but studies of BrC based on long-term observations are rather limited. In this study, we established a two-wavelength method (658 and 405 nm) applied in the Sunset thermal–optical carbon analyzer. Based on a 1-year observation, we firstly investigated the characteristics, meteorological impact and transport process of OC and EC. Since BrC absorbs light at 405 nm more effectively than 658 nm, we defined the enhanced concentrations (dEC = EC_405 nm − EC_658 nm) and gave the possibility of providing an indicator of BrC. The receptor model and MODIS fire information were used to identify the presence of BrC aerosols. Our results showed that the carbonaceous aerosol concentrations were the highest in winter and lowest in summer. Traffic emission was an important source of carbonaceous aerosols in Nanjing. Receptor model results showed that strong local emissions were found for OC and EC; however, dEC was significantly affected by regional or long-range transport. The $\mathrm{dEC}/\mathrm{OC}$ and $\mathrm{OC}/\mathrm{EC}$ ratios showed similar diurnal patterns, and the $\mathrm{dEC}/\mathrm{OC}$ increased when the $\mathrm{OC}/\mathrm{EC}$ ratios increased, indicating strong secondary sources or biomass burning contributions to dEC. A total of two biomass burning events both in summer and winter were analyzed, and the results showed that the dEC concentrations were obviously higher on biomass burning days; however, no similar levels of the OC and EC concentrations were found both in biomass burning days and normal days in summer, suggesting that biomass burning emissions made a great contribution to dEC, and the sources of OC and EC were more complicated. Large number of open fire counts from the northwestern and southwestern areas of the study site were observed in winter and significantly contributed to OC, EC and dEC. In addition, the nearby Yangtze River Delta area was one of the main potential source areas of dEC, suggesting that anthropogenic emissions could also be important sources of dEC. The results proved that dEC can be an indicator of BrC on biomass burning days. Our modified two-wavelength instrument provided more information than the traditional single-wavelength thermal–optical carbon analyzer and gave a new idea about the measurement of BrC; the application of dEC data needs to be further investigated.

中文翻译：

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使用两波长日落热光碳分析仪对含碳气溶胶进行高度时间分辨表征

碳质气溶胶对空气质量、人类健康和气候变化有很大影响。除有机碳（OC）和元素碳（EC）外，褐碳（BrC）主要来源于生物质燃烧，作为一组OC，对可见光到近紫外波长有很强的吸收，对全球变暖有相当大的贡献. 大量研究报告了世界各地对 OC 和 EC 浓度的长期观察，但基于长期观察的 BrC 研究相当有限。在这项研究中，我们建立了一种应用于 Sunset 热光碳分析仪的双波长方法（658 和 405 nm）。基于1年的观测，我们首先调查了OC和EC的特征、气象影响和迁移过程。 =  EC _{405 nm}  -  EC _{658 nm} ) 并提供了提供 BrC 指示剂的可能性。受体模型和 MODIS 火灾信息用于识别 BrC 气溶胶的存在。我们的结果表明，碳质气溶胶浓度在冬季最高，夏季最低。交通排放是南京市含碳气溶胶的重要来源。受体模型结果表明 OC 和 EC 存在强烈的局部排放；然而，dEC 受到区域或远程传输的显着影响。这$\mathrm{电离}/\mathrm{超频}$ 和 $\mathrm{超频}/\mathrm{欧共体}$ 比率显示出类似的昼夜模式，并且 $\mathrm{电离}/\mathrm{超频}$ 增加时 $\mathrm{超频}/\mathrm{欧共体}$比率增加，表明次要来源或生物质燃烧对 dEC 的贡献很大。对夏季和冬季共两次生物质燃烧事件进行了分析，结果表明，dEC浓度在生物质燃烧日明显偏高；然而，夏季生物质燃烧日和正常日的 OC 和 EC 浓度均未发现相似水平，表明生物质燃烧排放对 dEC 的贡献较大，且 OC 和 EC 的来源更为复杂。在冬季观察到来自研究地点西北部和西南部地区的大量明火计数，对 OC、EC 和 dEC 有显着贡献。此外，附近的长三角地区是 dEC 的主要潜在源区之一，表明人为排放也可能是 dEC 的重要来源。结果证明，dEC可以作为生物质燃烧天数的BrC指标。我们改进的双波长仪器比传统的单波长热光碳分析仪提供了更多的信息，并为BrC的测量提供了新的思路；dEC数据的应用需要进一步研究。