关键词: 开放光路, 差分吸收光谱技术, 车载走航观测, 无组织排放

Abstract: Objective　Unorganized emissions of atmospheric pollutants have the characteristics of random source location, uncertain emission timing and complex pollutant compositions, which means great challenges to conventional fixed-site monitoring with insufficient flexibility. Due to its flexibility and maneuverability, vehicle mobile platform monitoring has become a promising complementary technique for tracking toxic and harmful pollution components in the environment in recent years. Conventional pump-sampling monitoring systems suffer from unavoidable gas adsorption and sampling loss during pipeline transmission, which severely reduces measurement accuracy for trace odorants such as ammonia (NH₃) and dimethyl sulfide (CH₃SCH₃). To address this limitation, this work develops an open-path White-cell ultraviolet differential optical absorption spectroscopy (UV-DOAS) system based on mobile detection for real-time, loss-free field measurement of multi-component harmful atmospheric gases. The system's optical structure, spectral retrieval algorithm and field adaptability are comprehensively investigated, aiming to provide a high-sensitivity mobile monitoring tool for fugitive emissions from waste landfills and similar industrial sites. Methods　Unlike traditional gas extraction sampling techniques, open-path measurement not only eliminates the loss of analytes caused by sampling process, but also has the characteristics of high measurement precision, non-contact real-time online detection, and simultaneous quantification of multiple components. By regulating the number of beam reflections inside the White cell, effective optical path lengths ranging from 4.8 m to 33.6 m can be achieved with a base path length of approximately 1.2 m. Regarding the absorption characteristics of malodorous gases including ammonia (NH₃) and dimethyl sulfide (CH₃SCH₃) within the 190–240 nm wavelength range, a two-dimensional correlation matrix of differential absorption cross-sections was constructed for NH₃, CH₃SCH₃, sulfur dioxide (SO₂), carbon disulfide (CS₂), hydrogen sulfide (H₂S) and other absorbing species to screen the optimal retrieval wavelength band. Firstly, laboratory tests using the mixed gas of NH₃, CH₃SCH₃ and SO₂ were conducted to validate the selected wavelength range. And then, a vehicle-borne traverse campaign was carried out at a municipal landfill site in Hefei City in September 2023, and a spatial mass concentration distribution of target gaseous pollutants surrounding the landfill site was drawn by combining with Global Positioning System (GPS) positioning data. Finally, comparing with published literature data, correlation analysis and pollutant ratio analysis were carried out to characterize the emission patterns and pollution features of the landfills. Results and Discussion　The laboratory mixed-gas tests demonstrated that the relative deviation between the measured concentrations of each gas by this system and the standard theoretical values was below 3%, and the system achieved μg/m³ -level detection sensitivity for all target odorants and toxic gases. The field traverse observations successfully captured continuous spatial distribution data of four key pollutants around landfill boundaries. The maximum concentrations of NH₃, CH₃SCH₃, SO₂ and NO₂ in the atmosphere around the landfill site reached 74.9 μg/m³, 120.8 μg/m³, 423.3 μg/m³ and 451.2 μg/m³, respectively. Furthermore, the emission characteristics and pollution patterns of the landfill were investigated based on the correlation and ratio analysis of pollutant components. Significant concentration hotspots of NH₃ and CH₃SCH₃ were detected near the leachate exposure zones and waste transfer stations, and there was a strong positive correlation between the two gases, indicating consistent microbial decomposition-driven fugitive release. The high-concentration zones of SO₂ and NO₂ coincided with the downwind area of waste incineration facilities, and their stable concentration ratio matched the typical emission characteristics of domestic waste thermal treatment. The elevated NO ₂ signals also appeared at traffic congestion roads due to vehicle exhaust interference. The system maintained stable data output during vehicle vibration and mild rainfall periods, with a time resolution of 21 s, meeting the rapid response demand of mobile patrol monitoring. The comparative analysis of pollutant ratios across four landfills further distinguished the odor emissions from leachate and the flue gas pollutants from incineration units, clarifying the differentiated fugitive pollution patterns of different functional landfill areas. Conclusion　This study develops an open-path White-cell vehicle-monitoring UV-DOAS system with non-contact, realtime multi-component measurement and low sampling loss. This open-path White-cell UV-DOAS vehicle monitoring system overcomes the sampling loss defect of traditional extractive equipment and realizes adjustable long optical path measurement for trace harmful gases. The spectral interference elimination method based on cross-correlation matrices effectively improves the accuracy of simultaneous retrieval of NH₃, CH₃SCH₃, SO₂ and NO₂, which is fully validated through laboratory calibration. The field landfill traverse campaigns prove the system's outstanding environmental adaptability and spatial mapping capability for fugitive emissions. Combined with GPS location information, the system can accurately locate pollutant hotspots and distinguish multiple emission sources via inter-gas correlation and concentration ratios. This vehicleborne open-path DOAS platform provides a high-precision, high-sensitivity, real-time mobile monitoring scheme for on-site surveillance of fugitive toxic and malodorous atmospheric pollutants, and has broad application prospects in emission supervision of landfills, sewage plants and industrial parks.

Key words: open path, differential optical absorption spectroscopy (DOAS), mobile monitoring, unorganized emission