Research On Absorption Properties Of Atmospheric Aerosol Based On Photoacoustic Spectroscopy

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.