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

Laser photoacoustic spectrometry and a line permeation pollution source wer e used in a study of the dispersion of pollution in an urban agglomerate us ing simulation in a wind tunnel. Applications of this measuring technique u tilize the high sensitivity and broad dynamic range (3 orders of magnitude in this case) of the photoacoustic detection method. The minimum detected a bsorbance in the photoacoustic detection method employed in this work was a t the level of congruent to 4.3 x 10(-6) (congruent to 8 mu g 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 d eveloped in this work, with a concentration flux of (8.3 x 10(-5) +/- 2 x 1 0(-6)) g s(-1) at 20 degrees C, generated a concentration level in the mode l used from a background value of 80-90 mu g m(-3) up to values of congruen t to 1000 mu g m(-3) of methanol. A simple model street canyon together wit h the pollution source was employed to carry out a number of measurements o f spatial profiles. The dispersion of the pollutant was studied at the bott om and on the walls of the street canyon together with the concentration va riation with changes in the wind speed. The laboratory model was used to de monstrate the differences in ventilation of the street canyon.