双光路DOAS系统获取大气颗粒物粒谱分布方法研究

Study on the Number Size Distribution Retrieval of Atmospheric Particles with Double Optical Path DOAS

当前大气复合污染日趋严重,造成大气氧化性增强,气体向颗粒物的转化加快。大气颗粒物粒径大小及谱分布决定其在大气中的行为,以差分吸收光谱法(DOAS)为基础,结合双光路设计技术,开展实时、在线、获取近地面大气气溶胶颗粒物的粒谱分布的光谱方法研究。首先构建低噪声性能稳定的宽带氙弧灯为光源的双光路差分吸收光谱系统,基于干净天气条件下大气的能见度数据对系统进行校准,通过两个不同光路获得的光谱信号强度之比获取近地面紫外-近红外波段的大气总宽波段消光系数。基于宽波段消光系数,在去除瑞利散射以及气体吸收对消光系数的影响后,解析出气溶胶颗粒物的消光系数。基于核函数准则,利用均匀球型粒子的电磁场Mie理论来反演气溶胶物理特性,获得气溶胶粒子在该测量谱段的体积谱分布,利用体积谱与数密度谱的关系,反演出气溶胶粒子的数密度谱分布。开展利用直方图方法来表现颗粒物的粒谱分布方法研究,首先将DOAS测量波段近似等分为若干谱段,利用谱段处平均值,获取气溶胶粒谱直方分布图。最后把该系统和方法应用于外场实验,获得了气溶胶颗粒物在300~650nm范围内的消光系数,将测量波段等分为11个谱段,反演了颗粒物的在0.1~1.25μm粒径范围的数密度谱分布。该研究为整治我国灰霾天气,研究大气气相/粒子非均相化学反应提供科学依据。同时将推动DOAS技术的进一步发展和应用。

The atmospheric complex pollution becomes more and more serious,which results in atmospheric enhanced oxidation and accelerated transformation of gases into particles.The properties of atmospheric particles are determined by their radius range and number size distribution.A novel spectral method was developed for real-time,online and simultaneous determination concentrations of near-ground atmospheric pollution aerosols basing on differential optical absorption spectroscopy(DOAS), combining double optical path technique.The broadband xenon arc lamp is as light source of double optical path DOAS system. The differential optical absorption spectra are attained accurately using this system.The aerosol extinction coefficients are obtained by removal the contribution of polluted gas and Rayleigh scattering.Based on the kernel function criterion,the aerosol physical properties were retrieved using Mie scattering theory of uniform spherical particles.The aerosol size distribution and number density spectra distribution are retrieved by using aerosol extinction coefficients which have been got by DOAS system. The volume size distribution was retrieved by a step function(histogram).The number size distribution can be retrieved with the relationship the volume size distribution and the number size spectra.The inversion method was applied in the field experiment. The particle extinction coefficient was obtained from 300to 650nm.With the extinction coefficient,the number size distribution was retrieved.The particle radius ranges from 0.1to 1.25μm.The study can be used to analyze atmospheric particulate micophysical properties.Inversion method and remote sensing system are used in the field campaign.The research results not only can provide technique support to controll the haze weather,but also study atmospheric heterogeneous gas/particle chemical reaction to provide the raw data.The research will also promote further development and application of the DOAS technique.