State Key Laboratory of Cryospheric Sciences, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China.
University of Chinese Academy of Sciences, Beijing, 100049, China.
Environ Sci Pollut Res Int. 2017 Sep;24(26):21386-21397. doi: 10.1007/s11356-017-9688-8. Epub 2017 Jul 25.
Brown carbon (BrC) has recently received much attention because of its light absorption features. The chemical compositions, optical properties, and sources of fine aerosol at a high-elevation mountain observatory (4730 m a.s.l.) in the central Tibetan Plateau were measured between 31 May and 1 July 2015. A low flow-rate sampler was used to collect 24-h average fine particulate matter (PM) filter samples. Water-soluble ions, organic carbon (OC), elemental carbon, water-soluble organic carbon (WSOC), and light absorption by water-soluble BrC were determined for 26 filter samples. The mean (± 1σ) OC and WSOC concentrations were 0.76 ± 0.43 and 0.39 ± 0.15 μgC/m, respectively, and the mean WSOC/OC mass ratio was 0.59 ± 0.22. The OC and WSOC concentrations were relatively higher (0.59-1.80 and 0.33-0.83 μgC/m, respectively) during the pre-monsoon period (2-13 June) and were relatively lower (0.27-0.77 and 0.12-0.50 μgC/m, respectively) during the monsoon period (14 June to 1 July), probably because of wet scavenging of aerosols during long-range transport and the presence of cleaner marine air masses during the monsoon period. The absorption spectra of PM water extracts smoothly increase from visible range to ultraviolet range. The absorption Ångström exponent, which describes the wavelength dependence of water-soluble BrC, was 2.74-10.61 (mean 6.19 ± 1.70), and its value was similar in the pre-monsoon period (6.57 ± 0.56) to that in the monsoon period (5.91 ± 2.14). The water-soluble BrC mass absorption efficiency, 0.38 ± 0.16 m/(g C), was much lower than those observed in most urban areas but similar to those in other remote sites. Absorption coefficient at 365 nm, typically used as a proxy for water-soluble BrC, correlated well with the WSOC concentration (R = 0.57), K concentration (R = 0.75), and organic aerosol biomass burning markers characterized by an Aerodyne aerosol mass spectrometer (CHO + CHO, R = 0.60). It can be inferred that biomass burning was an important source of water-soluble BrC in the study area combined with air mass back trajectory analysis using the NOAA HYSPLIT as well as MODIS data of fire dots and aerosol optical depths. The water-soluble BrC to BC light absorption (at 365 nm) coefficient ratios were 9-27%.
棕色碳 (BrC) 因其光吸收特性而受到广泛关注。在青藏高原中部的一个高海拔山区观测站（海拔 4730 米），于 2015 年 5 月 31 日至 7 月 1 日期间测量了细气溶胶的化学组成、光学特性和来源。使用低流速采样器收集了 24 小时平均细颗粒物 (PM) 滤膜样品。对 26 个滤膜样品进行了水溶性离子、有机碳 (OC)、元素碳、水溶性有机碳 (WSOC) 和水溶性 BrC 的光吸收测定。OC 和 WSOC 的平均浓度分别为 0.76 ± 0.43 和 0.39 ± 0.15 μgC/m，WSOC/OC 质量比平均为 0.59 ± 0.22。OC 和 WSOC 浓度在 4 月 2 日至 13 日的前季风期（0.59-1.80 和 0.33-0.83 μgC/m）相对较高，在 6 月 14 日至 7 月 1 日的季风期（0.27-0.77 和 0.12-0.50 μgC/m）相对较低，这可能是因为气溶胶在长距离传输过程中受到湿清除作用，以及季风期存在更清洁的海洋空气团。PM 水提取物的吸收光谱从可见光范围平滑地增加到紫外线范围。描述水溶性 BrC 波长依赖性的吸收 Ångström 指数为 2.74-10.61（平均值为 6.19 ± 1.70），在前季风期（6.57 ± 0.56）与季风期（5.91 ± 2.14）相似。水溶性 BrC 质量吸收效率为 0.38 ± 0.16 m/(g C)，远低于大多数城市地区的观测值，但与其他偏远地区的观测值相似。365nm 处的吸收系数，通常用作水溶性 BrC 的替代物，与 WSOC 浓度（R = 0.57）、K 浓度（R = 0.75）以及由 Aerodyne 气溶胶质谱仪（CHO + CHO，R = 0.60）表征的有机气溶胶生物质燃烧标志物相关性良好。可以推断，结合使用 NOAA HYSPLIT 和 MODIS 火灾点和气溶胶光学深度数据进行的气团后轨迹分析，生物质燃烧是研究区域内水溶性 BrC 的一个重要来源。水溶性 BrC 与 BC 的光吸收（在 365nm 处）系数比为 9-27%。
