激光诱导辐射与弹性散射联合检测复杂介质中PM2.5的研究

Fine particulates such as PM2.5 receive much concern because of their effects on atmospheric environment, human health, combustion efficiency, etc. This project aims to the question how to rapid detect the concentration and size distribution of fine particulates in complicate media. The research subject will be combustionable gaseous flames and gas flue evolved by coal combustion. The research will be to study characteristic of time-resolved mixed spetral incandescence signal emitted by different sizes of fine particulates from the media which are lighted by the high power pulse laser. A nonlinear polynomial regression equation will be developed and the particlulates concentration and their size distribution in the media is characterized by the coefficients and decay time from the the equation. A coefficient correction algorithm will be developed to correct absorption and scattering effects of the coarse particles from the media which existing between the emission resource and the detector. A laser-based rapid detecting system with a wide range and high resolution will be established to measure the concentration of the fine particulates, such as PM 2.5 in the complicate media. The research results of this project will help to understand deeply the mechanisms of PM2.5 formation, growth, and evolution in atmospheric environment and the combustion resources such as industrial boilers and automobiles. These results will also provide scientific basis for creating reasonable combustion, allocating economical pollution control equipment, and developing PM2.5 control theory and technology.

PM2.5细粒子因对大气环境、人类健康、以及燃烧效率等的影响备受关注。本项目针对复杂介质中细粒子浓度与粒径的快速检测问题，以可燃气体火焰和燃煤烟气为研究对象，研究复杂介质经高能脉冲激光照射后不同尺度受热粒子激光诱导辐射出的光谱强度时间变化特性，建立非线性多项式回归方程，提取表征PM2.5细粒子浓度与粒径分布的特征参数。同时，采用激光弹性散射技术获取反映介质中粗颗粒组分特征量，建立系数修正算法，消除激光辐射信号发生源与检测器之间介质粗颗粒的吸收、散射对辐射光谱信号检测的干扰，建立适用范围较广、精度较高的激光测量系统，实现复杂介质中PM2.5细粒子浓度和粒径分布的快速检测。项目的研究成果对于深入理解大气环境以及工业锅炉、汽车等燃烧源PM2.5细粒子的形成、长大、演变机理等具有重要意义，为实时组织合理的燃烧、配置经济的污染控制设备、建立完善的PM2.5细粒子控制理论和技术提供科学依据。

PM2.5细颗粒因对大气环境、人类健康、以及燃烧效率等的影响备受关注。通过统计分析煤利用过程中PM2.5排放量发现，燃煤发电排放的PM2.5占煤利用过程中总排放量的60%以上，因此本项目以实验室燃煤火焰为研究对象，研究复杂介质中含碳PM2.5颗粒物浓度与粒径的激光检测问题。研究内容主要从理论模拟和实验测量两方面进行，详细论述了激光诱导辐射光谱技术（LII）在测量微纳米含碳颗粒粒径和浓度方面的应用。.结合弹性散射理论，采用核-壳模型计算含纤维素、石英、聚苯乙烯、赤铁矿及碳烟等五种不同典型凝结核霾滴的吸收效率因子，模拟计算结果揭示了内混态霾滴的光学吸收特性，表明含碳颗粒霾滴的吸收特性较其它矿尘霾滴的吸收特性更强，因此采用激光诱导辐射光谱技术可对煤等复杂介质燃烧产物中的吸收性较强的含碳颗粒物进行甄别和测量；同时建立了微纳米含碳颗粒的单相延迟双曲型激光诱导辐射传热传质模型，分析了含碳颗粒经高能脉冲激光照射前后温度与激光诱导辐射光谱强度的时域变化特征，为采用激光诱导白炽光技术进行高温环境中PM2.5含碳颗粒的定量测量研究提供理论依据，模型计算结果表明，热松弛时间取值越大，入射激光能量越高，粒径越小，受热颗粒的激光诱导辐射光谱信号振荡幅度越强，非傅里叶效应越显著。.实验层面主要是结合激光诱导白炽光法、消光法测量燃煤丙烷火焰中微纳米含碳颗粒的粒径分布和浓度，重点分析了测量波长、激光能量密度对激光诱导辐射信号的影响，实验结果表明，激光诱导辐射光谱信号强度在能量密度0.3 J/cm2、1.0 J/cm2时达到极大值，在0.5 J/cm2时达到极小值，这是纳米含碳颗粒升华辐射信号减弱和微米碳粒辐射白炽光信号叠加的综合结果。通过对辐射光混合信号衰减曲线进行三段指数函数拟合，确定三类含碳颗粒粒径分别为2 nm、21 nm和3 μm，分别对应为燃煤过程中的纳米碳粒、凝并或表面生长的成熟碳粒与焦炭或未燃尽煤粉等微米碳粒。结合消光法对LII信号强度标定得到三种粒径颗粒的平均体积浓度为0.18 ppm、0.16 ppm和0.19 ppm。该研究成果基本验证了联合激光诱导辐射光谱技术和散射技术探测PM2.5含碳颗粒颗粒粒径分布与浓度的可行性与可靠性。