Ram Kirpa, Sarin M M
Physical Research Laboratory, Ahmedabad - 380 009, India.
Environ Sci Technol. 2009 Nov 1;43(21):8233-9. doi: 10.1021/es9011542.
Temporal and spatial variability in the absorption coefficient (b(abs), Mm(-1)) and mass absorption efficiency (MAE, sigma(abs), m(2)g(-1)) of elemental carbon (EC) in atmospheric aerosols studied from urban, rural, and high-altitude sites is reported here. Ambient aerosols, collected on tissuquartz filters, are analyzed for EC mass concentration using thermo-optical EC-OC analyzer, wherein simultaneously measured optical-attenuation (ATN, equivalent to initial transmittance) of 678 nm laser source has been used for the determination of MAE and absorption coefficient. At high-altitude sites, measured ATN and surface EC loading (EC(s), microg cm(-2)) on the filters exhibit linear positive relationship (R(2) = 0.86-0.96), suggesting EC as a principal absorbing component. However, relatively large scatter in regression analyses for the data from urban sites suggests contribution from other species. The representative MAE of EC, during wintertime (Dec 2004), at a rural site (Jaduguda) is 6.1 +/- 2.0 m(2)g(-1). In contrast, MAE at the two high-altitude sites is 14.5 +/- 1.1 (Manora Peak) and 10.4 +/- 1.4 (Mt. Abu); and that at urban sites is 11.1 +/- 2.6 (Allahabad) and 11.3 +/- 2.2 m(2)g(-1) (Hisar). The long-term average MAE at Manora Peak (February 2005 to June 2007) is 12.8 +/- 2.9 m(2)g(-1) (range: 6.1-19.1 m(2)g(-1)). These results are unlike the constant conversion factor used for MAE in optical instruments for the determination of BC mass concentration. The absorption coefficient also shows large spatiotemporal variability; the lower values are typical of the high-altitude sites and higher values for the urban and rural atmosphere. Such large variability documented for the absorption parameters suggests the need for their suitable parametrization in the assessment of direct aerosol radiative forcing on a regional scale.
本文报道了在城市、农村和高海拔地区对大气气溶胶中元素碳（EC）的吸收系数（b(abs)，Mm⁻¹）和质量吸收效率（MAE，σ(abs)，m²g⁻¹）进行的时空变异性研究。收集在石英纤维滤膜上的环境气溶胶，使用热光EC-OC分析仪分析其EC质量浓度，其中同时测量的678 nm激光源的光学衰减（ATN，相当于初始透过率）用于测定MAE和吸收系数。在高海拔地区，滤膜上测得的ATN与表面EC负荷（EC(s)，μg cm⁻²）呈现线性正相关（R² = 0.86 - 0.96），表明EC是主要的吸收成分。然而，城市站点数据的回归分析中相对较大的离散度表明其他物种也有贡献。2004年冬季，农村站点（贾杜古达）EC的代表性MAE为6.1 ± 2.0 m²g⁻¹。相比之下，两个高海拔站点的MAE分别为14.5 ± 1.1（马诺拉峰）和10.4 ± 1.4（阿布山）；城市站点的MAE分别为11.1 ± 2.6（阿拉哈巴德）和11.3 ± 2.2 m²g⁻¹（希萨尔）。马诺拉峰（2005年2月至2007年6月）的长期平均MAE为12.8 ± 2.9 m²g⁻¹（范围：6.1 - 19.1 m²g⁻¹）。这些结果与光学仪器中用于测定BC质量浓度的MAE恒定转换因子不同。吸收系数也表现出较大的时空变异性；较低的值是高海拔站点的典型特征，而城市和农村大气中的值较高。吸收参数记录的这种大变异性表明，在区域尺度上评估直接气溶胶辐射强迫时，需要对其进行适当的参数化。
