【作者】 刘强；

【导师】 龚知本； 高晓明；

【作者基本信息】 中国科学技术大学 ， 光学， 2014， 博士

【摘要】 大气气溶胶通过吸收和散射太阳辐射影响大气辐射平衡,它对全球及局部地区的气候变化具有重要作用,因此精确测量大气气溶胶的光学特性对评估其辐射效应和气候效应的具有重要意义。光声光谱技术因其可直接测量自然悬浮状态下的气溶胶粒子、不受粒子散射影响等优点,被认为是进行气溶胶光吸收特性研究的有效手段。本文在光声光谱理论的基础上,设计了高性能的光声池,研制了一套可用于测量实际大气气溶胶吸收系数的光声光谱系统,通过对系统电噪声、流动噪声以及振动噪声的抑制,有效地提高了系统的灵敏度,并对吸收系数的标定以及系统的整体性能进行了系统研究。利用研制的系统,首先测量了实验室内产生的香烟气溶胶和苯胺黑气溶胶的光吸收特性,验证了系统的可靠性；然后,以合肥郊区的实际大气气溶胶为研究对象,通过长时问连续测量和多波长同时测量,结合扫描电迁移率颗粒物粒径谱仪的测量结果,详细分析了气溶胶粒子数浓度、粒径分布,以及化学成分的变化对测量气溶胶光吸收精度的影响。最后,为了开展大气气溶胶在中红外波段的吸收研究,利用可调谐外腔量子级联激光器对该波段实际大气中的CO2和N20以及CO和N20进行了同时探测,并对气体分子吸收和大气气溶胶吸收的同时探测进行了初步尝试。本论文的主要研究成果及创新有：(1)在国内率先研制了基于光声光谱技术的大气气溶胶吸收测量系统,对系统的噪声进行了分析,设计了消除采样管内振动噪声的微孔消音器,有效抑制了采样泵振动噪声的影响,并对系统的整体性能进行了实验研究和分析,为测量过程中采样流量的控制、数据采集频率的设定等参数提供了依据。在对吸收系数进行标定时,利用光谱仪测得的绿光激光器的发射谱和HITRAN数据提供的NO2吸收谱对单位浓度NO2的吸收系数进行了计算,使标定结果更加准确。(2)利用研制的光声测量系统,测量了实验室产生的香烟气溶胶和苯胺黑气溶胶的光吸收特性,对系统的可靠性进行了验证。然后,对合肥郊区实际大气气溶胶的吸收系数进行了长时间的测量,并分析了粒子数浓度、粒径分布以及气溶胶化学成分等因素对气溶胶吸收的影响。(3)提出了在存在水汽吸收干扰的波段测量大气气溶胶吸收系数的方法,利用该方法对香烟气溶胶和实际大气气溶胶在1.3μm附近的吸收进行了测量。(4)为了测量4.0μm波段大气气溶胶的吸收,我们利用4.5μm附近的外腔量子级联激光器首先对实际大气中CO2和N20以及CO和N20进行了同时探测,在此基础上对气溶胶吸收的测量进行了初步的研究。更多还原

【Abstract】 Atmospheric aerosols play an important role in atmospheric radiation balance through absorb and scatter the solar radiation, which changes local weather and global climate. Accurate measurement is highly requested to estimate the radiative effects and climate effects of atmospheric aerosol. Photoacoustic spectroscopy (PAS) technique, which observes aerosols on their natural suspended state and is insensitive to light scattering, is commonly recognized as one of the best candidates to measure the optical absorption coefficient (OAC) of aerosols.In the present work, a high performance PA cell was designed based on the PAS theory and a photoacoustic spectrometer was established for measuring the OAC of atmospheric aerosols. To improve the sensitivity, several methods was presented to control the noise derived from power supply, gas flow and vibration from the sampling pump. Calibration of the OAC and properties of the system were also studied in detail.Using the established PAS instrument, optical absorption properties of the cigarette smoke and nigrosin aerosol generated in laboratory were measured firstly to verify the reliability of the system. Then, time serial measurements and multi-wavelength measurements of the atmospheric aerosol at a suburban site of Hefei city were carried out. The effects of number concentration, size distribution and chemical composition on the OAC were analyzed in detail with the results from the PAS instrument and a scan mobility particle sizer. A method of measuring aerosol OAC at the wavelength where could also be absorbed by vapor was proposed and corresponding measurements were carried out.Finally, a tunable external cavity quantum cascade laser (EC-QCL) was used to determine CO2&N2O and CO&N2O simultaneously for the future work of aerosol absorption measurement at infrared wavelength. A preliminary study was carried out on the aerosol absorption measurement at infrared wavelength.The main merits and innovations of this thesis are as follows:(1)The PAS system for the aerosol OAC measurement developed in our library was the first one in China. A micro-hole mulffer was designed to control the noise derived from vibration from sampling pump. Performance of the PAS system was experimental investigated and analized. To calibrate OAC of aerosol accurately, absorption efficiency of NO2gas was calculated with emission spectrum of the green laser and absorption cross section provided by HITRAN2008database.(2)The PAS system was firstly employed to determine the optical absorption properties of cigarette smoke and nigrosin aerosol generated in laboratory to verify the reliability of the system. Then, time serial measurements and multi-wavelength measurements of the atmospheric aerosol at a suburban site of Hefei city were carried out.(3) A method of measuring aerosol OAC at the wavelength where could also be absorbed by vapor was proposed and corresponding measurements of the absorption properties of cigarette smoke and atmospheric aerosol near1.3μm were carried out.(4) To measure the absorption of atmospheric aerosol near4.5μm, a EC-QCL was employed to determine CO2&N2O and CO&N2O simultaneously firstly. Based on the trace gas measurements, absorption of aerosol was also studied preliminarily.更多还原