河北饶阳测点气溶胶细粒子散射、吸收特性及散射相函数的观测研究

发布时间：2018-08-17 15:59

【摘要】：气溶胶辐射特性是气溶胶辐射强迫研究中的重要参数,也是气溶胶辐射强迫估算中最大的不确定性来源之一。其中气溶胶散射相函数(不对称因子)反映了气溶胶对辐射散射的方向性,在辐射传输中有着特殊的重要性。多年来,有关气溶胶散射、吸收(消光)的观测研究已经开展了很多,然而对气溶胶散射相函数的直接观测研究还相对较少。本工作通过2014年6月16日至2014年8月18日在河北饶阳观测站点开展的综合观测试验,采用最新的商业化三波段角散射浊度仪(Polar Nephelometer),观测获得了当地的大气气溶胶细粒子(PM_(2.5))的角散射系数,进一步得到细粒子的散射相函数和不对称因子特征,并对同期获得的散射,吸收特性进行了分析。观测期间,饶阳干气溶胶细粒子的平均散射系数在450 nm,525 nm,635 nm三个波段分别为430.3±274.9 Mm~(-1)、403.8±274.7 Mm~(-1)和321.5±227.5Mm~(-1);525nm波长气溶胶细粒子的平均吸收系数为31±19 Mm~(-1),单次散射反照率为0.91±0.06,半球后向散射比0.13±0.03,Angstrom指数为1.00±0.36。反映了饶阳气溶胶细粒子具有较强的光散射性。饶阳测点污染的发生常伴有偏南方向的气流控制,颗粒物污染受到地面风和光化学过程的影响,不同风向条件下气溶胶光学性质的差异很大。根据多波长角散射浊度仪Aurora 4000(Polar Nephelometer,ECOTech,Australia)测量获取的前向角散射系数(10°~90°)和后向散射系数,提出了一种基于浊度仪直接测量的气溶胶角散射系数和改进的HG相函数近似获取气溶胶散射相函数、不对称因子的拟合估算方法。估算结果表明,用改进的HG相函数近似能够较好的拟合河北饶阳实际观测的气溶胶细粒子(PM_(2.5))的散射相函数,由此得到的前向(15-20度)散射相函数数值和半球后向散射比与通过角散射浊度仪直接测量得到的结果有很好的一致性。拟合得到河北饶阳测点观测期间干气溶胶细粒子在三个波长的平均不对称因子(g)分别为0.53±0.04(635nm)、0.57±0.05(525nm),和0.57±0.07(450nm)。对比观测期间两个污染和清洁过程,干气溶胶细粒子的散射相函数和不对称因子(g)在污染情况下明显高于相对清洁情况,表明饶阳地区污染情况下细粒子的平均粒径相比于清洁情况更大。利用多波长角散射浊度仪测量计算得到的气溶胶相函数和半球后向散射比的观测结果,结合同期膜采样气溶胶化学成分分析得到的平均复折射指数,对膜采样期间粒子谱分布进行拟合反演,并通过PM_1/PM_(2.5)膜称重的比值与利用拟合得到的粒子谱计算的PM_1/PM_(2.5)比值进行对比验证。结果表明,膜称重PM_1/PM_(2.5)的比值与利用拟合得到的粒子谱计算的结果具有较好的一致性,表明利用角散射浊度仪的测量结果反演细粒子的粒子谱分布有较好的效果。在此基础上,进一步采用拟合反演的粒子谱计算气溶胶细粒子的不对称因子。并且讨论分析了利用粒子谱计算和利用改进的HG相函数计算时,其误差函数算法中分别进行了对观测得到的相函数数据进行取对数处理和不取对数处理的试验。发现采用先拟合细粒子的谱分布,进而计算气溶胶细粒子的不对称因子的方法,能够得到数值上更稳定的不对称因子。
[Abstract]:Aerosol radiative characteristics are an important parameter in the study of aerosol radiative forcing and one of the greatest uncertainties in the estimation of aerosol radiative forcing. The aerosol scattering phase function (asymmetric factor) reflects the directivity of aerosol to radiative scattering and is of special importance in radiative transfer for many years. The study of aerosol scattering and absorption (extinction) has been carried out a lot, but the direct observation of aerosol scattering phase function is still relatively few. This work is based on the latest commercial three-band angular scattering turbidimeter (Polar Nephe) through a comprehensive observation experiment conducted at Raoyang Observatory from June 16, 2014 to August 18, 2014. The angular scattering coefficients of local fine aerosol particles (PM_ (2.5)) were obtained by lometer. The scattering phase functions and asymmetric factors of fine aerosol particles were further obtained. The scattering and absorption characteristics obtained at the same time were analyzed. During the observation period, the average scattering coefficients of Raoyang dry aerosol particles were 450 nm, 525 nm and 635 nm. The average absorption coefficient of fine aerosol particles at 525 nm wavelength is 31 (-1), the single scattering albedo is 0.91 (-1), the hemispheric backscattering ratio is 0.13 65507 Raoyang measurement point pollution is often accompanied by southward-facing airflow control. Particulate pollution is affected by surface wind and photochemical processes. The aerosol optical properties vary greatly under different wind directions. Based on the aerosol angular scattering coefficient measured directly by turbidimeter and the improved HG phase function, the aerosol scattering phase function and the asymmetry factor can be approximated and estimated. The results show that the improved HG phase function can be used to approximate the actual observation in Raoyang, Hebei Province. The forward (15-20 degree) scattering phase function and hemispheric backscattering ratio obtained from the scattering phase function of aerosol fine particles (PM_ (2.5)) are in good agreement with those directly measured by an angular scattering turbidimeter. The scattering phase function and asymmetry factor (g) of dry aerosol particles were significantly higher than that of the relative clean state in the pollution condition, indicating that the average particle size of dry aerosol particles in the pollution condition of Raoyang area was higher than that in the clean state. The results of aerosol phase function and hemispheric backscattering ratio measured by multi-wavelength angular scattering turbidimeter, combined with the mean complex refraction index obtained from the chemical composition analysis of aerosols sampled at the same time, were used to fit and invert the particle spectrum distribution during the film sampling period, and the ratio of PM_1/PM_ (2.5) film weighing and the average complex refraction index were obtained. The PM_1/PM_(2.5) ratio calculated by fitting the particle spectrum is compared and verified. The results show that the PM_1/PM_(2.5) ratio by membrane weighing is in good agreement with the calculated results by fitting the particle spectrum. It is shown that the results obtained by using the angular scattering turbidimeter have a better effect on retrieving the particle spectrum distribution of fine particles. On this basis, the asymmetric factors of aerosol fine particles are calculated by fitting and inversion of particle spectra, and the experiments of logarithmic processing and logarithmic processing of the observed phase function data are carried out in the error function algorithm when particle spectra and improved HG phase function are used. It is found that a more stable asymmetric factor can be obtained by fitting the spectral distribution of fine particles and then calculating the asymmetric factor of aerosol particles.
【学位授予单位】：中国气象科学研究院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513

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