光谱学与光谱分析, 2019, 39 (7): 1993, 网络出版: 2019-07-23   

呼吸性粉尘吸收系数的光声光谱探测

Study on Photo-Acoustic Spectrum Detection Technology of Respiratory Dust Absorption Coefficient
靳华伟 1,2,3,*谢品华 1,2胡仁志 1,2刘文清 1,2李治艳 1,2陈浩 1,2黄崇崇 1,2
作者单位
1 中国科学院安徽光学精密机械研究所环境光学与技术重点实验室, 安徽 合肥 230031
2 中国科学技术大学, 安徽 合肥 230026
3 安徽理工大学机械工程学院, 安徽 淮南 232001
摘要
针对呼吸性粉尘浓度连续、 可靠、 低成本的实时检测需求, 实现了光谱应用技术创新, 提出了一种基于光声光谱的呼吸性粉尘探测系统, 低功率二极管激光器光谱中心波长为403.56 nm及相应的NO2有效吸收截面为5.948 5×10-19 cm2·mole-1; 通过频率扫描拟合得到了1.35 kHz的谐振频率。 开展了光声池结构的影响分析, 得到了光声池长度参数对本底噪声影响较小但对激光信号影响较大、 内径参数对本底噪声存在一定影响但对本底噪声影响较小的结论。 在考虑品质因数、 加工条件、 使用场合和待测对象属性等影响情况下, 选用120 mm的长度参数和8 mm的内径参数; 基于长度为60 mm、 内径为25 mm的缓冲腔结构, 开展了缓冲隔板对系统稳定性的影响分析, 通过在缓冲腔中设置缓冲隔板, 降低了本底噪声、 稳定了系统, 其幅值及波动由(2.83±0.11) μv稳定为(1.26±0.03) μv。 分析得到了NO2的比吸收系数为195.28 Mm-1·(mg·m-3)-1, 利用NO2气体在405 nm处的吸收对系统进行了标定, 得到了拟合斜率为0.0436 8 μv/Mm-1、 相关系数为0.998、 池常数为300.24 Pa·cm·W-1的结论。 同时在1 min平均时间下, 得到了系统探测浓度下限及吸收系数为2.30 μg·m-3和0.448 Mm-1。 基于标准微球的聚苯乙烯作为气溶胶发生器对象开展了呼吸性粉尘的吸收系数影响分析, 进行了5μm以下不同数浓度颗粒及同一数浓度下不同粒径颗粒吸收系数的测试, 结果表明: 呼吸性粉尘的吸收系数和数浓度成正比, 线性拟合后的斜率为10.598±0.641 96, 相关系数为0.993; 吸收系数曲线的方差在3~4 Mm-1间, 不同粒径的颗粒对吸收系数存在着一定的影响; 随着粒径增加, 吸收系数随之增加。 开展了环境大气中NO2的测量, 选用0.2 μm的过滤膜滤除粉尘的干扰, 实验结果表明大气NO2浓度为16.4~61.6 μg·m-3, 平均浓度为41.1 μg·m-3。 为了证实测量系统的准确性, 与课题组自行研发的长光程差分吸收光谱系统(LP-DOAS)进行了对比测试, 测试结果显示了本光声光谱系统和LP-DOAS系统测量NO2浓度的相关性较好, 线性拟合后的斜率为1.011 78±0.040 13, 相关系数为0.947 81。 开展了环境大气中呼吸性粉尘的测量, 选用5 μm过滤片过滤环境大气, 通过“NO2+5 μm粉尘”和“NO2+0.2 μm粉尘”两路测量对象的差分测量, 得到了呼吸性粉尘的变化趋势, 可以满足自然悬浮状态下的呼吸性粉尘吸收系数实时测量。
Abstract
In this paper, combined with the continuous, reliable and low-cost real-time detection requirements of respiratory dust concentration, a spectral application technology innovation is realized, and the detection system with respiratory dust based on photo-acoustic spectroscopy is proposed. The center wavelength of the spectrum of the low-power diode laser is 403.56 nm and the corresponding effective absorption cross-section of NO2 is 5.948 5×10-19 cm2·mole-1. In addition, the resonance frequency of 1.35 kHz was obtained by using frequency scanning fitting. The influence analysis of photo-acoustic cell structure is carried out. The conclusion is drawn that the length parameter of the photo-acoustic cell has little influence on the background noise but great influence on the laser signal and the inner diameter parameter has some influence on the background noise but little influence on the background noise. Considering the influence of quality factors, processing conditions, service occasions and properties of the objects to be tested, length parameters of 120 mm and inner diameter parameters of 8 mm are selected. Besides, based on the buffer cavity structure with a length of 60 mm and an inner diameter of 25 mm, the influence of buffer partition on system stability is analyzed. The background noise is reduced and the signal fluctuation isoptimized from (2.83±0.11) to (1.26±0.03) μv. The specific absorption coefficient of NO2 with 195.28 Mm-1·(mg·m-3)-1 is analyzed. The system is calibrated using NO2 gas absorption at 405 nm. The fitting slope is 0.043 68 μv/Mm-1, the correlation coefficient is 0.998, and the pool constant is 300.24 Pa·cm·w-1. At the same time, the lower limit of the detected concentration and the absorption coefficient are 2.30 μg·m-3 and 0.448 Mm-1. The influence of absorption coefficient of respirable dust on polystyrene based on standard microspheres as aerosol generator is analyzed. What’s more, the absorption coefficients of particles with different concentration and different diameters at the same concentration are measured. The absorption coefficient of respirable dust is directly proportional to the number concentration. The slope after linear fitting is 10.598±0.641 96, and the correlation coefficient is 0.993. The variance of the absorption coefficient curve is between 3~4 Mm-1, and the absorption coefficient is affected by particles of different particle sizes. At the same time, the absorption coefficient increases with the increase of particle size. The NO2 measurements have been carried out in the ambient atmosphere. The filter membrane with 0.2 μm has been used to remove dust interference. The experimental results show that the concentration of NO2 in the atmosphere is 16.4~61.6 μg·m-3, and the average concentration is 41.1 μg·m-3. In order to verify the accuracy of the measurement system, the long-path differential absorption spectrum system developed by our group is compared. The test results show that there is a good correlation between the concentration of NO2 measured by the photo-acoustic spectroscopy system and the LP-DOAS system. The slope after linear fitting is 1.011 78±0.040 13, and the correlation coefficient is 0.947 81. The respirable dust in the ambient atmosphere is measured. The filter membrane with 5 μm is selected to filter the ambient atmosphere. The “NO2+5 μm dust” and “NO2+0.2 μm dust” are measured. The change trend of respirable dust is obtained, which can satisfy the real-time measurement of respirable dust absorption coefficient under natural suspension state.

靳华伟, 谢品华, 胡仁志, 刘文清, 李治艳, 陈浩, 黄崇崇. 呼吸性粉尘吸收系数的光声光谱探测[J]. 光谱学与光谱分析, 2019, 39(7): 1993. JIN Hua-wei, XIE Pin-hua, HU Ren-zhi, LIU Wen-qing, LI Zhi-yan, CHEN Hao, HUANG Chong-chong. Study on Photo-Acoustic Spectrum Detection Technology of Respiratory Dust Absorption Coefficient[J]. Spectroscopy and Spectral Analysis, 2019, 39(7): 1993.

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