POLARIS Research Center, Department of Environmental Sciences, University of Milan-Bicocca, Piazza della Scienza 1, Milan, Italy.
Sci Total Environ. 2011 Jun 15;409(14):2824-37. doi: 10.1016/j.scitotenv.2011.04.022. Epub 2011 May 5.
Vertical profiles of aerosol number-size distribution and black carbon (BC) concentration were measured between ground-level and 500m AGL over Milan. A tethered balloon was fitted with an instrumentation package consisting of the newly-developed micro-Aethalometer (microAeth® Model AE51, Magee Scientific, USA), an optical particle counter, and a portable meteorological station. At the same time, PM(2.5) samples were collected both at ground-level and at a high altitude sampling site, enabling particle chemical composition to be determined. Vertical profiles and PM(2.5) data were collected both within and above the mixing layer. Absorption coefficient (b(abs)) profiles were calculated from the Aethalometer data: in order to do so, an optical enhancement factor (C), accounting for multiple light-scattering within the filter of the new microAeth® Model AE51, was determined for the first time. The value of this parameter C (2.05±0.03 at λ=880nm) was calculated by comparing the Aethalometer attenuation coefficient and aerosol optical properties determined from OPC data along vertical profiles. Mie calculations were applied to the OPC number-size distribution data, and the aerosol refractive index was calculated using the effective medium approximation applied to aerosol chemical composition. The results compare well with AERONET data. The BC and b(abs) profiles showed a sharp decrease at the mixing height (MH), and fairly constant values of b(abs) and BC were found above the MH, representing 17±2% of those values measured within the mixing layer. The BC fraction of aerosol volume was found to be lower above the MH: 48±8% of the corresponding ground-level values. A statistical mean profile was calculated, both for BC and b(abs), to better describe their behaviour; the model enabled us to compute their average behaviour as a function of height, thus laying the foundations for valid parametrizations of vertical profile data which can be useful in both remote sensing and climatic studies.
在米兰，从地面到 500 米高空，对气溶胶数-尺度分布和黑碳 (BC) 浓度的垂直分布进行了测量。系留气球上配备了一个仪器包，其中包括新开发的微吸光光度计 (微吸光计® AE51 型， Magee Scientific，美国)、光学粒子计数器和便携式气象站。同时，在地面和高空采样点采集了 PM(2.5) 样品，从而确定了颗粒的化学成分。在混合层内外都收集了垂直剖面和 PM(2.5) 数据。从吸光光度计数据中计算了吸收系数 (b(abs)) 剖面：为此，首次确定了一个光学增强因子 (C)，用于新的微吸光计® AE51 型过滤器内的多次光散射。该参数 C 的值 (λ=880nm 时为 2.05±0.03) 通过比较吸光光度计衰减系数和垂直剖面中 OPC 数据确定的气溶胶光学特性来计算。米氏计算应用于 OPC 数-尺度分布数据，气溶胶折射率通过应用于气溶胶化学成分的有效介质近似法来计算。结果与 AERONET 数据吻合较好。BC 和 b(abs) 剖面在混合层高度 (MH) 处急剧下降，MH 以上的 b(abs) 和 BC 值相当恒定，占混合层内测量值的 17±2%。MH 以上的气溶胶体积中 BC 分数较低：为相应地面值的 48±8%。为了更好地描述它们的行为，计算了 BC 和 b(abs) 的统计平均值剖面；该模型使我们能够计算它们作为高度的函数的平均行为，从而为垂直剖面数据的有效参数化奠定了基础，这在遥感和气候研究中都很有用。
