Spatial Distributions of Trace Gases and Aerosol Particles over the Coastal Megacity of Metro Manila, Philippines during the CAMP2Ex Aircraft Campaign

As a consequence of rapid economic development, several megacities in Southeast Asia (SEA) host rising levels of air pollution that require an in-depth characterization to guide pollution mitigation strategies. Aircraft-based pollution measurements serve to bridge the gap between local ground-based sampling and large-scale satellite retrievals, but airborne data is relatively scarce in SEA. To partially address this shortfall, an in-depth aircraft-based investigation under the NASA Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP²Ex) was performed over and downwind of Metro Manila on 4 Oct 2019. This provides the first in-depth, three-dimensional spatial analysis of air pollution over Metro Manila, a rapidly-growing coastal megacity characterized by its complex local meteorology, high population density, elevated pollution levels, and high black carbon (BC) contribution to fine particulate pollution.

Preliminary analysis showed elevated concentrations of CO₂, CH₄, and CO associated with winds and back trajectories originating from Metro Manila. Low-altitude (100 m above ground level; AGL) enhancement ratios of these species, accompanied by regime changes in aerosol composition, suggested the presence of three distinct emission profiles. Over the megacity, trace gas concentrations were generally highest near the surface (150 m AGL), particularly near industrial areas.

Further work will include other trace gases (e.g., NO_x, NO_y, O₃) and aerosol species (e.g., SO₄^2-, BC) to investigate possible sources such as power plants and landfills. Investigating the spatial distributions of key species and identifying possible emission sources of pollution in and around Metro Manila lends valuable insights on the spatial characteristics and transport of pollution over coastal megacities, serving as a case study of urban pollution in SEA as well as helping us quantify the contribution of Metro Manila to regional pollution.