Indoor CO2 Online Monitoring Based on Open-Path Tunable Diode Laser Absorption Spectroscopy

To investigate the variation in indoor carbon dioxide ( CO2) volume fractions and their relationship with human activities, this study designs an open-path tunable diode laser absorption spectroscopy (TDLAS) sensing system to monitor indoor CO2 volume fractions. A distributed feedback ( DFB) laser with a central wavelength of 2004 nm is employed as the excitation light source to measure the R(16) characteristic absorption line of carbon dioxide. The Levenberg-Marquardt method of nonlinear least squares fitting is employed to fit the measured spectra, allowing for volume fraction measurements without requiring calibration. Comparative measurements with a commercial XENSIVTM PAS CO2 sensor yield a high correlation (R-2= 0. 89). The results indicate that the daily average indoor CO2 volume fraction is 4. 63x10(-4), slightly surpassing outdoor levels, whereas the fluctuation range of indoor CO2 volume fraction within a day is 3. 86x10(-4). 5. 66x10(-4). Indoor CO2 volume fraction is volume fractions influenced by ventilation and indoor human activities, and the daily volume fraction trends are highly correlated with working hours. At a personnel density of 0. 005 persons/m(3), the growth rate of CO2 volume fraction is measured at 2. 3x10-5 h(-1). Therefore, timely ventilation is recommended for crowded indoor environments to prevent elevated CO2 volume fractions that may cause discomfort.