矿物沙尘是气溶胶的重要化学组分， 对气候和环境都有重要影响。 本文基于2010年的北京AERONET站点的气溶胶产品资料， 分析了复折射指数在440～1 020 nm范围内的变化特性， 发现实部(n)在各个波段的取值差异不大； 而虚部(k)由于受到矿物沙尘吸收的影响从440到670 nm呈现出明显下降的趋势。 据此， 将k(440 nm)与其他波段的值分开考虑， 增加了一维信息量， 从而能将目前基于复折射指数反演气溶胶化学组成的三组分模型(水、 黑碳、 硫酸铵)扩展为包含矿物沙尘的四组分模型， 解决了以往在粗粒子较多时无法进行化学成分反演的难题。 针对北京沙尘、 灰霾、 晴朗三种典型天气进行了气溶胶中沙尘组分的反演试验， 获得的体积比例分别为88%， 37%和48%， 与基于气溶胶粒子体积谱分布计算的粗粒子比例的相对大小具有很好的一致性。

Mineral dust is an important chemical component of aerosol, which has a significant impact on the climate and environmental changes. The spectral behavior of aerosol refractive indices at four wavelengths from 440 to 1 020 nm was analyzed based on one year observation obtained from Beijing AERONET site. The real parts of refractive index (n) in each band did not differ greatly, however the imaginary parts (k) showed a significant difference due to the absorption of mineral dust in aerosol. From 440 to 670 nm k decreased rapidly, while from 670 to 1 020 nm featured a lower, constant value. Accordingly, k(440 nm) could be considered separately with other three bands. Hence, we added mineral dust into the currently used three-component aerosol chemical model to form a new four-component model (i.e. BC, AS, dust and water) which is more suitable to represent the aerosol chemical composition. Then we presented a method to retrieve dust content in aerosols using this four-component model and refractive indices obtained from the sunphotometer measurements. Finally the dust content in aerosol was investigated under different weather conditions, i.e. clear, haze and dust in Beijing. The results showed that volume fractions of the dust component were 88%, 37% and 48% for clear, hazy and dusty day respectively, which was consistent with the coarse mode proportion in aerosols calculated from aerosol size distributions.