Studies Of The Planetary Boundary Layer And Their Impact On Air Pollution In A Semi-Arid Region With Complex Terrain

The adjacent cities of El Paso-Juárez, located in the Rio Grande Rift Valley and surrounded by complex mountainous terrain, have undergone rapid urbanization and industrial growth in the last few decades, accompanied by increasing substandard air quality episodes. Although numerous air quality studies were conducted in this semi-arid region in the past, none focused extensively on the Planetary Boundary Layer (PBL) contribution and impact on air pollutant concentrations. In this work, both the high and low ozone episodes from 2015 to 2020 were examined. Both modeling and experimental data of the PBL height (PBLH) were obtained and related to atmospheric stability. Aerosol backscattered data from a network of ceilometers were used to monitor and continuously measure the aerosol-layer characteristics. PBLH of 2700 ± 250 m was frequently observed during the summer, with occasional extraordinarily high PBLH (3780 ± 250 m) days. Out of 29 high ozone events during the study period where ceilometer PBLH were analyzed, 23 events had shallow daytime PBLH indicating less volume for pollution dispersion. Synoptic scale analysis of these events supported this claim and revealed an anticyclonic circulation aloft associated with a middle and upper tropospheric high-pressure system centered within 750 km of this region. The resultant significant scale subsidence strengthened the temperature inversion capping the PBL growth, thus trapping the pollutants. A comprehensive case study of the 2017 consecutive high and low ozone episodes provided a better understanding of meteorology and PBL in regional pollution events. During the entire study, the ceilometer also captured several occurrences of virga events (a phenomenon within the PBL) in this region, and a simple method of virga detection is proposed. All the observed virga events occurred in Fall and Winter months with favorable dry climatic conditions