Urban daytime boundary layer height determination and its relationship with high pollutant concentrations in Barcelona

Abstract

The planetary boundary layer height (PBLH) is a key parameter to diagnose the amount of pollutant concentration since it takes part in vertical dispersion, limiting the volume where the pollutants can be dispersed. Nevertheless, there is not a reference technique to compute it. In this work, 4 different algorithms -Parcel Method (RSD0), Gradient Detector (WW), Function Adjustment (ERES) and BL-View Enhanced Gradient using a Candidate Selector (CEIL)- are applied to Barcelona non-rain midday radiosounding and ceilometer data from August 2015 to December 2018 in order to estimate PBLH, focusing on pollutant episodes. The results suggest that RSD0 algorithm use is more suitable during summer, when boundary layer is highly developed. Instead, CEIL yield better results during colder seasons, when boundary layer is not highly developed and, thus, noise do not dominate over backscatter signal. WWis useful to detect strong temperature gradients and ERES is e ective at detecting cloud presence. Among the four algorithms, WW and CEIL are selected to study high pollution concentration days. The PBLH median for NO2 and PM10 episodes is lower than the 25th percentile for all days studied, which suggest the role of low PBLH in pollutant accumulation. WW and CEIL point higher PBLH for tropospheric O3 episodes influenced by high temperature and clear sky conditions.