获取大气颗粒物消光系数的差分吸收光谱法研究

Extinction Coefficient Measurement of Atmospheric Particles with Differential Optical Absorption Spectroscopy

针对雾霾天气日益增多,大气污染气体向颗粒物的转化在加快,研究了一种大范围对其监测的差分吸收光谱方法。差分吸收光谱法可以实时、在线、准确同时获取颗粒物光学特性和大气痕量气体浓度。论文首先分析了双光路差分吸收光学遥感系统获取颗粒物绝对光强的原理,然后研究了基于单光路测量大气吸收谱,在干净天气状况下测量参考光谱,利用能见度数据,在550nm波段处实现系统校准,计算校准参数,从而获得大气绝对吸收光强,然后解析出大气总的消光系数。再从总的大气消光系数中,去除瑞利散射以及大气痕量气体吸收对消光系数影响后,精确解析出颗粒物消光系数。同时基于差分思想获取大气痕量气体的浓度。最后把该方法应用于外场实验,获取大气颗粒物在350~700nm波段范围内消光系数和大气中NO2的浓度。研究结果表明颗粒物消光系数的随着波长的增加而减少,符合Angstrom公式。该研究为分析大气气相/粒子非均相化学反应提供有力的技术支持。

The atmospheric complex pollution becomes more and more serious, which results in enhanced atmospheric oxidation and accelerated interconversion of pollution trace gases and particles. Differential optical absorption spectroscopy （DOAS） is developed to monitor the characteristics of atmospheric particles in a large scale. The method of differential optical absorption spectroscopy is applied to real-time, online and simultaneous determination concentrations of atmospheric trace gases and extinction coefficients of particles. Method of extinction measurement of atmospheric particles is discussed basing on double optical paths DOAS system. The single optical path DOAS system is discussed for measuring the particle extinction coefficients in this paper. The DOAS system need to be calibrated to measure particle extinction. Firstly, the reference spectrum is measured under the clean atmospheric condition with visibility data. Then the absorption intensity of 550 nm wavelength is recorded to obtain correction coefficient of the the DOAS system. The total absolute optical intensity of atmosphere can be retrieved after calibrating the system parameter. The particle extinction coefficients are obtained by removing the contribution of trace gases and Rayleigh scattering from the total optical intensity. The particle extinctions are obtained from 350 to 700 nm and trace gases concentrations of NO2 are simultaneously retrieved basing on differential principle in the field campaign. The particle extinction coefficients decrease with wavelengths, which is in accordance with Angstrom formula. The research can provide raw data support to study atmospheric heterogeneous gas/particle chemical reaction.