Influence of wind direction and source location on peak-to-mean concentration ratios in urban environments

Abstract

Peak values of concentration can occur during very short time intervals due to atmospheric turbulence. The power law function can be used to relate the mean concentration (
over a longer time period
to the maximum mean concentration (
corresponding to a shorter time period
; however, it has not yet been fully investigated in urban areas where buildings can affect the turbulent airflow and mass transfer of pollutants. This work examines the power law function exponent (p) considering different urban scenarios: a uniform building height array and a tall building embedded in a regular array, considering different wind directions and source locations. The results show that, increasing fetch, the peak-to-mean concentration ratio usually decreases with increasing averaging time. For the same wind direction, sources located in the urban canyon produce lower |p|-values compared to the source located between buildings. Oblique flows present lower |p|-value comparing to perpendicular direction. It is fair to state that although there is an influence of wind direction and source location, the distance from the source promotes larger variations of p. For the tall building configuration, the peak-to-mean ratios as well as the |p|-values were lower compared with the uniform building height array.

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ORCID for Zheng-Tong Xie: orcid.org/0000-0002-8119-7532

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