LP-DOAS测量乙二醛时大气中干扰吸收的去除

针对利用长光程差分吸收光谱技术在实现对大气中乙二醛实时监测中,一些干扰结构（Xe灯结构,H2O、NO2和O4干扰吸收）对长光程差分吸收光谱技术的影响,讨论了乙二醛的光谱反演方法对干扰吸收的准确去除.针对Xe灯结构由于压力和多普勒展宽程度等的变化而引起的Xe灯结构的非线性变化,采用不同时刻的参考灯谱通过光谱插值的方式准确去除,其去除误差引起的剩余结构可降低到比乙二醛的最低理论检测限低3倍|针对H2O的非线性吸收以及特征吸收结构随柱浓度的不同而变化的特点,采用较高和较低浓度H2O吸收光谱插值的方法准确去除了严重干扰乙二醛准确反演的H2O的吸收结构,其去除误差引起的剩余结构可降低到比乙二醛的最低理论检测限低10倍|另外,对于在此波段存在干扰的NO2和O4的吸收结构也实现了准确地去除.干扰结构的准确去除使DOAS对乙二醛的监测实现了较低的实际检测限 (0.15 ppbv)和较低的测量误差 (~10 %).最后,在广州郊区对实际大气进行了实际监测,其浓度范围在低于检测限到1.66 ppbv之间,与文献报道的浓度范围和变化趋势十分吻合.

Elimination of Atmospheric Interfering Absorption for the Measurement of Glyoxal by LP-DOAS*

  When measuring glyoxal directly in the atmosphere by Long Path Differential Optical Absorption Spectroscopy (LP-DOAS),the analysis of glyoxal strongly suffers from the cross interference of other absorbers or structure (Xe lamp-structure,H2O,O4 and NO2 absorption).The retrieval method of glyoxal-the elimination of interfering absorption or structure was studied.The Xe lamp-structure will change nonlinearly resulted from the change of pressure broadening and Doppler Broadening with the change of of Xe lamp pressure or temperature.The different lamp reference spectra detected at different time were interpolated to eliminate lamp structure and the resulting residual structures caused by an incorrect elimination were a factor of three below the detection limit of glyoxal|high amount of H2O in the atmosphere cause the nonlinear absorption of H2O and the observed band shape to vary with the column density of H2O.Two H2O absorption spectra with higher and lower column density were interpolated to eliminate nonlinear H2O absorption and the resulting residual structures caused by an incorrect elimination were ten times below the detection limit of glyoxal.In addition,the strong absorption of interfering species NO2 and O4 were also accurately removed.Low detection limit (0.15 ppbv) and low systematic errors (~10 %) were achieved by the accurate elimination of interfering structures.In the end,glyoxal was routinely detected during the daytime on the outskirts of Guangzhou,where mixing ratios ranged from less than detection limit (0.15 ppbv) to 1.66 ppbv.The variation and range of glyoxal concentration detected agreed well with the results reported.