Optical properties of tropospheric aerosol and sulfate scattering efficiency measured at Neumayer Station, Antarctica

We measured optical properties and ionic composition of the aerosol at Neumayer Station from 2004 through 2006 by an integrating nephelometer and chemical analysis of daily aerosol samples, respectively. From this unique data set we discuss the seasonality of aerosol optical parameters along with their chemical composition. Austral summer (November through March) was characterized by mean particle number concentrations of 472±260 cm**-3 compared to 168±160 cm**-3 during winter (April through October), mean scattering Ångström exponents of 1.7±0.6 compared to 1.3±0.6 during winter, and mean backscattering ratios at 700 nm of 0.21±0.13 compared to 0.17±0.08 during winter. In contrast, light scattering coefficients (ssp) showed a broad maximum during winter (4.8±5.3 1/µm for ssp(550)). The mean single scattering albedo was 0.99± at 550 nm. We further derived mass scattering and mass backscattering efficiencies for biogenic sulfate aerosol (BSA) at 450 nm, 550 nm, and 700 nm for relative humidities between 5% and 11%. At 550 nm the scattering efficiency for biogenic sulfate aerosol sigma bsBSA(550) was 8.9±0.7 m**2/g with a corresponding backscattering efficiency sigma bsBSA(550) of 1.0±0.08 m**2/g. From the seasonality of the aerosol composition we inferred a dominant contribution of sulfate aerosol regarding radiative forcing in the lower troposphere from December through January at Neumayer, while the impact of sea salt aerosol prevailed for the rest of the year.本研究于2004至2006年间，在诺伊迈尔站（Neumayer Station）分别采用积分浊度计（integrating nephelometer）与每日气溶胶样品化学分析法，测定了该站点气溶胶的光学特性与离子组成。基于这套独特的数据集，本研究探讨了气溶胶光学参数及其化学组成的季节变化特征。南半球夏季（11月至次年3月）的平均粒子数浓度为472±260 cm⁻³，冬季（4月至10月）则为168±160 cm⁻³；平均散射安斯特朗指数为1.7±0.6，冬季为1.3±0.6；700 nm波长下的平均后向散射比为0.21±0.13，冬季为0.17±0.08。与之相对，光散射系数（light scattering coefficients, ssp）在冬季呈现宽泛的峰值，其中550 nm处的ssp(550)为4.8±5.3 1/µm。550 nm波长下的平均单散射反照率为0.99±。本研究进一步推导了相对湿度介于5%至11%区间内，生物源硫酸盐气溶胶（biogenic sulfate aerosol, BSA）在450 nm、550 nm及700 nm处的质量散射效率与质量后向散射效率。在550 nm波长下，生物源硫酸盐气溶胶的散射效率σ_bsBSA(550)为8.9±0.7 m²/g，对应的后向散射效率σ_bsBSA(550)为1.0±0.08 m²/g。基于气溶胶组成的季节变化特征，本研究推断：在诺伊迈尔站，12月至次年1月期间，硫酸盐气溶胶对低层对流层辐射强迫的贡献占据主导地位；而全年其余时段，海盐气溶胶的影响则更为显著。