Impact of planetary boundary layer in dense haze /smog event over South Asian Mega City; Lahore Pakistan

Air quality over North Eastern region of Pakistan is rapidly worsening over the years, especially over Lahore and adjacent areas reporting world record levels of pollutant concentrations including highest particulate matter (PM) levels during the autumn and winter seasons. Meteorological parameter plays an important role in extreme pollution episodes. In order to study the impact of meteorological condition such as planetary boundary layer (PBL) an intensive PBL measurements were conducted over Lahore from October 2019 to March 2021 using LUFT CHM15K Ceilometer LIDAR. The impacts of PBL structure on heavy haze pollution and the relationship with PM2.5 concentrations were studied. The boundary layer height drops clearly during winter period (December 2019 and 2020, usually lower than 500m. The PM2.5 concentrations increases when the PBL drops and vice versa. Key finding in this study is that the dynamics of the Planetary Boundary Layer (PBL) change significantly during heavily polluted days during intense autumn / winter smog periods, which indicates the role of aerosols in influencing meteorological conditions, besides having other impacts in the region of study.