Abstract
The planetary boundary layer height (PBLH) is one of the key factors in influencing the dispersion of the air pollutants in the troposphere and, hence, the air pollutant concentration on ground level. For this reason, accurate air pollutant concentration depends on the performance of PBLH prediction. Recently, ceilometers, a lidar instrument to measure cloud base height, have been used by atmospheric scientists and air pollution control authorities to determine the mixing level height (MLH) in improving forecasting and understanding the evolution of aerosol layers above ground at a site. In this study, ceilometer data at an urban (Lidcombe) and a rural (Merriwa) location in New South Wales, Australia, were used to investigate the relationship of air pollutant surface concentrations and surface meteorological variables with MLH, to validate the PBLH prediction from two air quality models (CCAM-CTM and WRF-CMAQ), as well as to understand the aerosol transport from sources to the receptor point at Merriwa for the three case studies where high PM10 concentration was detected in each of the three days. The results showed that surface ozone and temperature had a positive correlation with MLH, while relative humidity had negative correlation. For other pollutants (PM10, PM2.5, NO2), no clear results were obtained, and the correlation depended on the site and regional emission characteristics. The results also showed that the PBLH prediction by the two air quality models corresponded reasonably well with the observed ceilometer data and the cause and source of high PM10 concentration at Merriwa can be found by using ceilometer MLH data to corroborate back trajectory analysis of the transport of aerosols to the receptor point at Merriwa. Of the three case studies, one had aerosol sources from the north and north west of Merriwa in remote NSW, where windblown dust is the main source, and the other two had sources from the south and south east of Merriwa, where anthropogenic sources dominate.
Highlights
The planetary boundary layer (PBL) is considered as the lowest layer of the troposphere directly influenced by the surface forcing, such as heat transfer, frictional drag, topography, and others
The selected meteorological variables from the DPIE Lidcombe monitoring station showed that temperature and solar radiation were strongly correlated with mixing level height (MLH), as shown in Figures 3 and 4
The inverse relation between temperature with relative humidity explains the MLH is positively correlated with temperature, but negatively correlated with RH
Summary
The planetary boundary layer (PBL) is considered as the lowest layer of the troposphere directly influenced by the surface forcing, such as heat transfer, frictional drag, topography, and others. The term MLH indicates boundary layer height as measured by lidar such as Vaisala CL51, while PBLH indicates layer height predicted from the models or measured with temperature profiles, such as from radiosonde. PBLH from the DPIE’s forecast and air quality models, CCAM-CTM study, we used the derived MLH data from the two selected ceilometers to compare with The PBLH is an important parameter in predicting air quality concentration and, as such, comparison with MLH lidar measurement data from the ceilometer is performed. Besides using the ceilometer measurement to validate the PBLH estimate in air quality models, ceilometers can detect aerosol at various heights above a site, continuously, and they are useful to study aerosol transport.
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