Laser photoacoustic spectrometry and its application for simulation of air pollution in a wind tunnel

Abstract

Laser photoacoustic spectrometry and a line permeation pollution source were used in a study of the dispersion of pollution in an urban agglomerate using simulation in a wind tunnel. Applications of this measuring technique utilize the high sensitivity and broad dynamic range (3 orders of magnitude in this case) of the photoacoustic detection method. The minimum detected absorbance in the photoacoustic detection method employed in this work was at the level of ≅ 4.3 × 10^–6 (≅ 8 µg m^–3 CH₃OH). The effectiveness and flexibility of the permeation method for generation of various concentrations of gases were verified for simulation of emission pollution sources in a wind tunnel. The line permeation pollution source developed in this work, with a concentration flux of (8.3 × 10^–5 ± 2 × 10^–6) g s^–1 at 20 °C, generated a concentration level in the model used from a background value of 80–90 µg m^–3 up to values of ≅ 1000 µg m^–3 of methanol. A simple model street canyon together with the pollution source was employed to carry out a number of measurements of spatial profiles. The dispersion of the pollutant was studied at the bottom and on the walls of the street canyon together with the concentration variation with changes in the wind speed. The laboratory model was used to demonstrate the differences in ventilation of the street canyon.