On the association between characteristics of the atmospheric boundary layer and air pollution concentrations

Air pollution in the lower atmosphere is a global concern. Characteristics of the planetary boundary layer (PBL) are considered important determinants of the dispersion and the concentrations of pollutants. This work explores the association between characteristics of the PBL and corresponding air pollution data, separately for different PBL states. Five years (2014-2018) of twice daily (01:30 and 13:30 local time) high resolution radiosonde data were used to estimate the convective and stable boundary layer heights (CBL and SBL, respectively), and the temperature lapse rate, in Bet Dagan, Israel. In 23% of the nights, mostly cloudy ones, no indication for an SBL was found but a clear top of a ground-based residual layer (RBL) was detected. The concentrations of NO, NO2, NOx and PM2.5 were negatively correlated with the heights of the CBL and RBL but positively correlated with the SBL height. Their association with the lapse rate was always negative, weak in daytime (CBL) but very strong during the night (SBL and RBL). The associations with the O-3 concentrations were opposite in sign to those with the primary pollutants. The PBL height using the bulk Richardson number method was most strongly associated with the CBL and RBL concentrations but we found it unsuitable for estimating the height of the SBL. Our results demonstrate the importance of accounting for the different states of the PBL. In particular, they suggest that during SBL conditions, the common practice of using the PBL volume as a determinant of pollutant concentrations might not be appropriate.