First Simultaneous Visualization of SO2 and NO2 Plume Dispersions using Imaging Differential Optical Absorption Spectroscopy

Imaging Differential Optical Absorption Spectroscopy (Imaging-DOAS) has been utilized in recent years to provide slant column density (SCD) distributions of several trace gas species in the plume. The present study introduces a new method using Imaging-DOAS data to determine two-dimensional plume structure from the plume emissions of power plant in conditions of negligible aerosol effects on radiative transfer within the plume. We demonstrates for the first time that two-dimensional distributions of sulfur dioxide ($SO_2$) and nitrogen dioxide ($NO_2$) in power plant emissions can be determined simultaneously in terms of SCD distribution. The $SO_2$ SCD values generally decreased with increasing distance from the stack and with distance from the center of the plume. Meanwhile, high $NO_2$ SCD was observed at locations several hundred meters away from the first stack due to the ratio change of NO to $NO_2$ in NOx concentration, attributed to the NO oxidation by $O_3$. The results of this study show the capability of the Imaging-DOAS technique as a tool to estimate plume dimensions in power plant emissions.