大气颗粒物光散射特性的理论和实验研究

【作者】 李燕； 薛锐； 陶培培；

【机构】 南京理工大学化工学院； 南京工程学院能源与动力学院；

【摘要】 大气颗粒物的光散射在能见度降低和气候变化方面起主要作用。大气中颗粒物的组成和结构非常复杂,因此,对于大气颗粒物光散射的预测是一个不确定性非常大的难题。本文以海洋区域大气中主要的无机盐颗粒物NaNO₃和NaCl为例,研究大气中α-蒎唏与O₃光化学反应生成的低挥发性二次气溶胶（SOA）包覆无机盐颗粒物后,对其光散射性质的影响。采用TSI 3563积分浊度仪测量包覆前后的气溶胶颗粒物对450,550和700nm光的散射能力,同时采用经典的Mie核-壳双层结构光散射理论预测光散射系数。研究结果表明,当SOA包覆层的厚度相对于无机盐颗粒物的直径非常小时,有机包覆层对核光散射性质的影响可以用Mie核-壳理论模型得到较好的预测。对于固定的无机盐颗粒物直径,当有机物的相对含量增加时,光散射能力减弱。因此,对于特定粒径分布的无机物盐颗粒物,当有机物组分增加时,光散射能力将会降低,相对于纯的盐颗粒物,这将减轻它们对能见度的影响,但是也会抵消由于温室气体引起的对流层变暖。更多还原

【Abstract】 Light scattering by airborne particles plays a major role in visibility degradation and climate change.The composition and structure of particles in air can be complex,so that predictions of light scattering a priori have significant uncertainties.We report here studies of light scattering by NaNO₃ and NaCl,a model for airborne salt particles from the ocean and alkaline lakes,with and without an organic coating formed from the low volatility products of the reaction of α-pinene with ozone at room temperature at 1 atm in air.Light scattering at 450,550 and 700 nm was measured using an integrating nephelometer on particles whose size distribution was independently determined using a scanning mobility particle sizer（SMPS）.For comparison,polystyrene latex spheres（PSL） of a known size and dioctylphthalate（DOP） particles generated with a narrow size distribution were also studied.The measured values were compared to those calculated using Mie theory.Although excellent agreement between experiment and theory was found for the PSL and DOP particles,there were large discrepancies for a polydisperse NaCl sample.Combination of experiments and theory show that as salt takes up low volatility organics in the atmosphere and the geometric mean diameter increases,the effect on light scattering may be reasonably approximated from the change in size distribution under conditions where the organic coating is small relative to the core size.However,for a given particle diameter,light scattering decreases as the relative contribution of the organic component increases.Thus,light scattering by salt particles with a specific size distribution will be reduced when organics comprise a significant portion of the particles.This will lessen their impact on the visual range compared to pure salt particles,but also lead to less counterbalancing of the troposphere warming due to greenhouse gases.更多还原