RESUMO
This paper presents the simulation and field evaluation results of two approaches to localize pollutant emission sources with open-path Fourier transform infrared (OP-FTIR) spectroscopy. The first approach combined the plume's peak location information reconstructed from the Smooth Basis Function Minimization (SBFM) algorithm and the wind direction data to calculate source projection lines. In the second approach, the plume's peak location was determined with the Monte Carlo methodology by randomly sampling within the beam segment having the largest path-integrated concentration. We first conducted a series of simulation studies to investigate the sensitivity of using different basis functions in the SBFM algorithm. It was found that fitting with the beta and Weibull basis functions generally gave better estimates of the peak locations than with the normal basis function when the plumes were mainly within the OP-FTIR's monitoring line. However, for plumes that were symmetric to the peak position or spread over the OP-FTIR, fitting with the normal basis function gave better performance. In the field experiment, two tracer gases were released simultaneously from two locations and the OP-FTIR collected data downwind from the sources with a maximum beam path length of 97 m. For the first approach, the release locations were within the 0.25- to 0.5-probability area only after the uncertainty of the peak locations was included in the calculation process. The second approach was easy to implement and still performed as satisfactorily as the first approach. The distances from the sources to the best-fit lines (i.e., the regression lines) of the estimated locations were smaller than 10 m.
Assuntos
Poluentes Ocupacionais do Ar/análise , Poluição do Ar/prevenção & controle , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Vento , Poluição do Ar/análise , Algoritmos , Simulação por ComputadorRESUMO
This paper reports the results from a field study that used a micro gas chromatograph (µGC) in conjunction with single gas chromatography-mass spectrometry (GC-MS) analysis to obtain the time-dependent concentration changes of individual volatile organic compounds (VOCs). The µGC is capable of performing sub-ppb analysis every 15min and has a total weight of only 3kg, which includes an embedded tablet computer. The field study was conducted in an elementary school near a chemical industrial area. Six VOCs including acetone, 2-butanone, methyl acetate, toluene, m-xylene and isobutyl acetate, were detected at low ppb levels via canister/GC-MS analysis. Five of the six chemicals were successfully quantified using the µGC. The lone exception was acetone, which prematurely breakthrough on the preconcentrator of the µGC because of its high volatility. The continuous analyses performed by the µGC revealed the individual temporal trends of the concentrations for the remaining 5 chemicals. The establishment of real-time trends for each of the chemicals enabled a detailed examination of their correlations.
Assuntos
Poluentes Atmosféricos/análise , Poluição do Ar em Ambientes Fechados/análise , Monitoramento Ambiental/métodos , Compostos Orgânicos Voláteis/análise , Poluição do Ar em Ambientes Fechados/estatística & dados numéricos , Butanonas/análise , Cromatografia Gasosa , Cromatografia Gasosa-Espectrometria de Massas , Instituições Acadêmicas , Xilenos/análiseRESUMO
A new approach employing two pollution rose plots to locate the sources of multiple hazardous gas emissions was proposed and tested in an industrial area. The data used for constructing the pollution rose plots were obtained from two side-by-side measurements of open-path Fourier Transform Infrared (OP-FTIR) spectrometers during one week of continuous analysis on the rooftop of a semiconductor plant. Hazardous gases such as CF4, C2F6, CH3OH, NH3, NO2, and SF6 were found and quantified at the ppb level by both OP-FTIR measurement sites. The data of the top 20% highest concentrations and associated wind directions were used to construct the pollution rose plots. Pollution source probability contours for each compound were constructed using the probability-product of directional probability from two pollution rose plots. Hot spots for SF6, CF4, NO2, and C2F6 pointed to the stack area of the plant, but the sources of CH3OH and NH3 were found outside of this plant. The influences of parameters for this approach such as the variation in wind direction, lower limit concentration threshold and the nearby buildings were discussed.