Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad, 380009, India.
Stockholm University, 11419, Stockholm, Sweden.
Environ Sci Pollut Res Int. 2020 Sep;27(26):33339-33350. doi: 10.1007/s11356-020-09388-7. Epub 2020 Jun 12.
Light-absorbing organic aerosol (brown carbon (BrC)) can significantly affect Earth's radiation budget and hydrological cycle. Biomass burning (BB) is among the major sources of atmospheric BrC. In this study, day/night pair (10-h integrated) of ambient PM were sampled every day before (defined as T1, n = 21), during (T2, n = 36), and after (T3, n = 8) a large-scale paddy-residue burning during October-November over Patiala (30.2° N, 76.3° E, 250 m amsl), a site located in the northwestern Indo-Gangetic Plain (IGP). PM concentration varied from ~ 90 to 500 μg m (average ± 1σ standard deviation 230 ± 114) with the average values of 154 ± 57, 271 ± 122, and 156 ± 18 μg m during T1, T2, and T3 periods, respectively, indicating the influence of BB emissions on ambient air quality. The absorption coefficient of BrC (b) is calculated from the high-resolution absorption spectra of water-soluble and methanol-soluble organic carbon measured at 300 to 700 nm, and that at 365 nm (b) is used as a general measure of BrC. The b and b ranged ~ 2 to 112 Mm (avg 37 ± 27) and ~ 3 to 457 Mm (avg 121 ± 108), respectively, suggesting a considerable presence of water-insoluble BrC. Contrasting differences were also observed in the daytime and nighttime values of b and b. Further, the levoglucosan showed a strong correlation with K (slope = 0.89 ± 0.06, R = 0.92) during the T2 period. We propose that this slope (~ 0.9) can be used as a typical characteristics of the emissions from paddy-residue burning over the IGP. Absorption Ångström exponent (AAE) showed a clear day/night variability during the T2 period, and lower AAE compared to AAE throughout the sampling period. Further at 365 nm, average relative atmospheric radiative forcing (RRF) for BrC is estimated to be ~ 17%, whereas that of BrC ~ 62% with respect to elemental carbon, suggesting that BrC radiative forcing could be largely underestimated by studies those use BrC only as a surrogate of total BrC.
吸光有机气溶胶（棕色碳 (BrC)）会显著影响地球的辐射收支和水文循环。生物质燃烧 (BB) 是大气 BrC 的主要来源之一。在这项研究中，每天在 10 小时的大气 PM 日/夜对（T1，n=21）之前、期间（T2，n=36）和之后（T3，n=8）采集环境 PM，在 10 月至 11 月期间，一个位于印度西北部恒河平原（IGP）的 Patiala（30.2°N，76.3°E，250 m 海拔）的大型稻田燃烧之后。PM 浓度在 90 到 500 μg m 之间变化（平均值±1σ标准偏差 230±114），T1、T2 和 T3 期间的平均值分别为 154±57、271±122 和 156±18 μg m，表明 BB 排放对环境空气质量的影响。从 300 到 700nm 测量的水溶性和甲醇溶性有机碳的高分辨率吸收光谱计算 BrC 的吸收系数（b），并将 365nm 处的 b 用作 BrC 的一般测量值。b 和 b 的范围分别为2 到 112 Mm（平均值 37±27）和3 到 457 Mm（平均值 121±108），这表明存在大量不溶于水的 BrC。b 和 b 的日夜间值也存在明显差异。此外，在 T2 期间，左旋葡聚糖与 K 呈强相关性（斜率=0.89±0.06，R=0.92）。我们提出，这个斜率（~0.9）可以作为 IGP 稻田燃烧排放的典型特征。在 T2 期间，吸收 Ångström 指数（AAE）表现出明显的日/夜变化，并且与整个采样期间的 AAE 相比，AAE 较低。此外，在 365nm 处，BrC 的平均相对大气辐射强迫（RRF）估计约为 17%，而 BrC 相对于元素碳的 RRF 约为 62%，这表明 BrC 的辐射强迫可能被那些仅将 BrC 用作总 BrC 替代物的研究大大低估。
