Development and application of UV-visible and mid-IR differential absorption spectroscopy techniques for pollutant trace gas monitoring

摘要: Spatial representativeness is an important quality criterion in trace gas monitoring, especially if measurements are intended for regulatory and model validation purposes. Open-path absorption spectroscopy techniques meet the requirement by providing concentrations averaged over atmospheric paths ranging from some hundred meters to kilometers. This research concerns characterization application of a UV-visible differential optical (DOAS) system, development demonstration detection technique based on tunable, mid-infrared (mid-IR) quantum-cascade lasers (QCL). The spectral accuracy, stability resolution DOAS spectrometer, efficiency its PMT1-based light system were characterized tested laboratory field conditions. Additional experiments included exploratory test photodiode array (PDA) as multichannel analyzer, analysis arc high-pressure Xe lamps. PDA NO2 360-530 nm range show effective lower detectable fractional absorbance 8·10-4 (1-sigma) 3-s integration time, overpassing capabilities scanner/PMT system. SO2, NO2, O3 extensively validated through calibration intercalibration, intercomparison with conventional point monitors EPA2-certified systems, showing good agreement among different instruments. A nitrous acid (HONO) generator was developed used characterizing capability. Laboratory indicate limit (LDL)  0.2 ppm·m HONO (2-sigma) 30-min time. Concerning formaldehyde (HCHO), HPLC3-analyzed DNPH4 samples shows non-aleatory, high degree correlation (r2 = 97%) between two techniques, but unexplained, significant deviation 1:1 line (which nevertheless within 85% confidence interval curve). mathematical method estimation limits sequential lamp spectra. LDL estimations this very operational limits. Other data processing concentration retrieval algorithms analyzing (12 campaigns). interpretation observations these studies reported detail. first study dynamics photochemical production regime HCHO Grenoble region, France. at suburban location allowed estimating sources formaldehyde, served validating results mesoscale grid model. Measurement-derived emission ratios literature values, inventory, calculations. large fraction (>80%) observed measurement photochemically produced, VOC-limited / NOx-saturated. investigation demonstrates also that well-suited second monocyclic aromatic hydrocarbons (MAH) wastewater treatment plant Lausanne (Switzerland) using GC5/FID6-analyzed grab samples. Combined vertical wind speed MAH time series suggest quasi-diurnal cycle involving accumulation fugitive emissions during stagnant early morning hours followed rapid upward convective dispersion midday on. indicates potentially source area. Measurements carried out altitude ( 2500 m ASL7) Andean valley (Sogamoso Valley, Colombia) presented interpreted. combined meteorological performed ground level (including DOAS) airborne (with homemade tethered balloon), along calculations, provide evidence inflow Sogamoso Valley clean air masses Colombian Eastern Savanna ( 200 ASL). anabatic flow plays role ventilation valley, particularly dry season. Despite selectivity sensitivity, temporal resolution, restricted limited number species display highly structured electronic bands. advent laser (QCL) 1994, thereafter, offers open-path promising doorway mid-IR. Quantitive ambient pressure 9.6 µm pulsed-operated, single-mode DFB8 QCL demonstrated transmission spectra 1044-1050 cm-1 obtained tuning temperature. column densities retrieved mid-IR simultaneous attained ( 25 ppm·m) still too immediate open path Currently ongoing improvements pulse acquisition should allow achieving commercial systems ( 2 near future. These demonstrate applicability encourage use detection. -------------------------------------------------- 1 PMT: PhotoMultiplier Tube 2 EPA: US Environmental Protection Agency 3 HPLC: High Performance Liquid Chromatography 4 DNPH: 2,4-DiNitroPhenylHydrazine 5 GC: Gas 6 FID: Flame Ionization Detector 7 ASL: Above Sea Level 8 DFB: Distributed FeedBack