Accurate Inversion of Formaldehyde Column Concentration in a Chemical Park Based on a Passive Vehicle-Mounted DOAS System
HU Zhao-kun1，2, LI Ang1*, XIE Pin-hua1，2，3, WU Feng-cheng1, XU Jin1
1. Key Laboratory of Environment Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
2. Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China
3. CAS Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
Abstract：Formaldehyde (HCHO) is the most abundant carbonyl compound in the atmosphere. It is one of the most important intermediate products of non-methane volatile organic compounds. It is widely involved in photochemical reactions in the atmosphere and is also an important precursor of aerosols. Formaldehyde plays an important role in atmospheric chemistry. The emission of VOCs from the petrochemical industry is an important source of HCHO in the urban atmosphere. At present, the pollutants of NMVOCs such as HCHO in the chemical park are mainly near-ground concentration through point-type equipment and lack of stereoscopic monitoring data. The Differential Optical Absorption Spectroscopy technology has been successfully applied to the monitoring of pollutant gases such as SO2 and NO2. Due to the relatively weak optical absorption intensity of formaldehyde, the cross-interference of other gases in the inversion band is strong, and practical monitoring applications are relatively rare. The paper selects a petrochemical company and uses a passive DOAS method to accurately invert formaldehyde column concentrations. In this paper, the relationship between the absorption profile of formaldehyde and other two-dimensional correlation matrix that is used to fit the gas absorption cross-section is established, and the band with the smallest correlation between the absorption profile of formaldehyde and other gas absorption profiles is selected. The acquisition of the band that minimizes cross-interference from DOAS inversion of formaldehyde by other gases is achieved. At the same time, the spectrum actually collected in the field is selected, and different initial bands and cut-off bands are selected for iterative DOAS inversion. The residuals are used to evaluate the actual inversion effect of formaldehyde in different bands. In the region where the cross-interference between the cross-sections is small and the fitting residual is low, the widest band is selected as the best fitting band to achieve accurate DOAS inversion of formaldehyde. From the results of the two-dimensional correlation matrix of absorption profiles of formaldehyde and other gases, the correlation between formaldehyde and NO2, SO2, O3, and O4 is below 0.5 in most of the bands, and the cross-interference is small. The correlation between formaldehyde and BrO at the initial wavelength of 318～320 nm, cutoff wavelength of 340～346 nm and initial wavelength of 330～334 nm, and cutoff wavelength of 354～360 nm is less than 0.5 in these two wavebands, which is suitable as the inversion waveband of HCHO. Through the selection of different initial bands and cut-off bands for the iterative DOAS inversion of formaldehyde, combined with the correlation analysis results of fitting cross sections, 332.4～358.1 nm was finally used as the inversion band of HCHO, and the fitting residual was 10-4. In this paper, a passive vehicle-borne DOAS system is used to establish the HCHO best-fit band for the system by establishing a two-dimensional correlation matrix between absorption cross-sections and through iterative inversion of the measured spectrum. The fitting residual is reduced to 10-4. Based on the accurate inversion of formaldehyde and combined with GPS information of the system, the spatial distribution of formaldehyde concentration in a chemical company was acquired. During the entire field observation period, the error of HCHO inversion was less than 6%. The results show that the vehicle passive DOAS system can play an important role in quickly obtaining the spatial distribution information of formaldehyde in the chemical industry park, and provides an effective measurement method for the stereoscopic monitoring of formaldehyde in the urban atmosphere.
Key words：Air pollution; Chemical industry park; DOAS; Fitting band; HCHO
胡肇焜，李 昂，谢品华，吴丰成，徐 晋. 基于车载被动DOAS系统的化工园区甲醛柱浓度精确反演研究[J]. 光谱学与光谱分析, 2019, 39(10): 3028-3033.
HU Zhao-kun, LI Ang, XIE Pin-hua, WU Feng-cheng, XU Jin. Accurate Inversion of Formaldehyde Column Concentration in a Chemical Park Based on a Passive Vehicle-Mounted DOAS System. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(10): 3028-3033.
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