Lidar observations of the diurnal variations in the depth of urban mixing layer: A case study on the air quality deterioration in Taipei, Taiwan
Journal
Science of the Total Environment
Journal Volume
374
Journal Issue
1
Pages
156-166
Date Issued
2007
Author(s)
Abstract
An aerosol light detection and ranging (LIDAR) system was used to measure the depth of the atmospheric mixing layer over Taipei, Taiwan in the spring of 2005. This paper presents the variations of the mixing height and the mixing ratios of air pollutants during an episode of air quality deterioration (March 7-10, 2005), when Taipei was under an anti-cyclonic outflow of a traveling high-pressure system. It was found that, during those days, the urban mixing height reached its daily maximum of 1.0-1.5 km around noon and declined to 0.3-0.5 km around 18:00 (LST). In terms of hourly averages, the mixing height increased with the ambient temperature linearly by a slope of 166 m/°C in daytime. The consistency between the changes in the mixing height and in the ambient temperature implied that the mixing layer dynamics were dominated by solar thermal forcing. As the cap of the mixing layer descended substantially in the afternoon, reduced dispersion in the shallow mixing layer caused the concentrations of primary air pollutants to increase sharply. Consequently, the pollutant concentration exhibited an anti-correlation with the mixing height. While attentions are usually focused on the pollution problems occurring in a morning inversion layer, the results of this study indicate that the air pollution and its health impacts could be even more severe as the mixing layer is getting shallow in the afternoon. © 2006 Elsevier B.V. All rights reserved.
Subjects
LIDAR; Tropospheric aerosols; Urban air quality; Urban mixing layer
SDGs
Other Subjects
Air pollution; Atmospheric aerosols; Geographical regions; Mixing; Optical radar; Anti-cyclonic outflow; Light detection and ranging (LIDAR); Pollutant concentration; Tropospheric aerosols; Urban air quality; Urban mixing layer; Air quality; aerosol; air quality; air temperature; atmospheric pollution; diurnal variation; lidar; solar radiation; urban atmosphere; vertical mixing; aerosol; air analysis; air monitoring; air pollutant; air pollution; air quality; article; atmosphere; circadian rhythm; dynamics; environmental temperature; light; priority journal; Taiwan; urban area; Aerosols; Air Pollutants; Air Pollution; Environmental Monitoring; Meteorological Factors; Seasons; Taiwan; Asia; Eurasia; Far East; Taipei; Taiwan
Type
journal article