.op-ftir/ct Technology Application In The Monitoring Of Atmospheric Pollutants

Open Path Fourier Transform Infrared Spectroscopy (OP-FTIR) combined with computed tomography (CT) is an innovative technique that can be used for occupational and environmental air monitoring. The followings are the major content of this paper:1. A novel iterative algorithm, least-squares with non-negativity constraints (LSNC), was developed for reconstructing chemical concentration distributions using the OP-FTIR system. The reconstructions were evaluated by different quantitative criteria of image quality, and compared with a conventional iterative method--the maximum likelihood expectation maximization (MLEM) that had been approved to be able to create accurate maps for steeper plumes. Results showed that the reconstruction quality for narrow plumes by LSNC method was dramatically improved over MLEM method, especially in the peak location estimation. Additionally, this method improved the reconstruction accuracy of concentration maps quantitatively and qualitatively when the plumes were under some constraints, including the rapid changing air flow patterns and the simulated measurement noise.2. Acetone gas was scanned rapidly for 40 times in a chamber using the OP-FTIR technique, and the observed path integrated concentrations (PICs) and bootstrapped PICs data were reconstructed using LSNC method. The experiments validated LSNC can locate peaks more accurately than MLEM, and the reconstructed PICs were more closer to the original data. What's more, the bootstrapped reconstructions were found to be better when compared to original reconstructions. Furthermore, the bootstrap method may present some useful information that was lost due to the instrument limits.3. Using computer simulation data and time series analysis, this study demonstrated that it is feasible to use the OP-FTIR/CT technique to evaluate personal exposures, in terms of 26min time-weighted average concentration (26min TWA) personal exposures. The correlation coefficient (R_TWA²) between the estimated and true values depended on the simulation conditions. When we have a relatively wide plume and slowly changing conditions, the R_TWA² values are high and close to 1. On the contrary, the R_TWA² values are smaller when the plume is narrow with fast changing conditions. This paper...