PBLH and Wind Effects on Diurnal PM2.5 Surface Concentrations in Metro Manila during CAMP2Ex Weather and CompoSition Monitoring 2019

This study investigated the effects of planetary boundary layer height (PBLH) and near-surface winds on the observed aerosol loading within the PBL, during daytime for no-rain days over an urban mixed background site in Metro Manila from January to December 2019. A unique opportunity wherein collocated measurements from a ground-based High Spectral Resolution Lidar (HSRL), Beta Attenuation Monitor, and automated weather station at the Manila Observatory (MO; 14.64°N, 121.08°E) were obtained from the Cloud, Aerosol Monsoon Processes Philippines Experiment (CAMP2Ex) Weather and CompoSition Monitoring observation campaign. The HSRL vertically-resolved aerosol column and PBLH retrievals together with PM2.5 surface concentration measurements provided novel observations of the air quality above the surface. Results show that PM2.5 surface concentrations can be representative of the immediate 500-m aerosol column in terms of diurnal variability with a Pearson correlation R = 0.63. PBLH and the 500-m aerosol column have a significant inverse relationship with R = -0.37. Further analysis also revealed the compounding effects of winds, PBLH and traffic volume on the observed high surface aerosol loading especially in the morning. Shallow PBLH and low near-surface wind speeds in the mornings both constrain and stagnate the fresh emissions to a small PBL volume, which leads to poor air quality in the site. Meanwhile, mid-afternoons are characterized by larger PBLH and near-surface wind speeds, which leads to a reduction of mean PM2.5 concentrations by a factor of two as compared to the mornings.