Over the last decade, an accurate assessment of ambient air quality in Metro Manila has never been really possible due to the absence of a consistent monitoring program. As a result, adverse effects on public health, economic productivity, infrastructure, and vegetation have never been comprehensively assessed. While air quality monitoring has been initiated in the past (e.g. URBAIR, 1997) most of these have been transient exercises and have never been really sustained over the long term (except for the Environmental Management Bureau-National Capital Region, which has been continuously monitoring total suspended particulates for a number of years now).

Partial monitoring of criteria air pollutants (such as SO₂, NO₂, O₃, CO, Pb, and PM10) in the past have shown that PM10 and O₃ are the pollutants of concern in the city.

This study, through the support of SIDA, has focused on investigating the severity of fine particulate matter (PM2.5), a major component of PM10. In particular, the spatial and temporal distribution of fine PM was assessed via the monitoring and modeling activities of this study. Despite the absence of an ambient guideline in the Philippine Clean Air Act for this particular pollutant, the study was undertaken because it is more dangerous than PM10.

With these scientific results, it is now possible to evaluate adverse effects on public health, infrastructure, economic productivity, and vegetation. The conclusions will hopefully provide a more reasonable and credible basis for developing sound policies that will improve air quality in Metro Manila.

According to the results of three years of fine PM monitoring and source-receptor modeling, the most significant source of particulate pollution in Metro Manila is the transport sector.

This sector's contribution is consistently substantial, varying from 50 to 90 per cent at various sampling sites in the city all throughout the year. Next to transport, sources such as biomass burning, sea salt, and soil have also been found to contribute, in varying degrees, to particulate pollution.

Source inventory of PM also confirms the significance of the transport sector in the particulate pollutant load of Metro Manila.

• PM 2.5 levels are most serious in three sites, namely NPO (traffic site), Pasig (industrial), and PGH (commercial/institutional). Despite the absence of AQ ambient standards for PM2.5, it is likely that Metro Manila will be in non-attainment for PM because of this.
• Source apportionment (of PM2.5 by CMB and PMF) indicates that the primary contribution to particulate pollution is from the transport sector. This is evident even in clean background sites such as Antipolo.

• Dispersion modeling results indicate the serious but localized contribution of stationary sources to particulate pollution over the northwestern part of Metro Manila. These also point to the extensive contribution of mobile (i.e. transport-related) sources throughout the city. Major pollution hotspots are found to be concentrated along major arteries and dense traffic networks (such as those in the central part of the city).
• The significant contribution of transport (or mobile sources) is also substantiated by an initial inventory of PM sources.

• Improve and expand urban railway system (including ancillary infrastructure such as parking areas)
• Continue improving public vehicular volume control along major roads

• Implement rapid and extensive conversion to natural gas
• Phase out two-stroke motorcycle engines by supply and demand-side measures

• Pedestrianize areas in and around urban attractors
• Utilize riverine transport
• Construct bicycle lanes where possible

• Institute eco-labeling of buses, jeeps, cars, and tricycles
• Strengthen and improve motor vehicle inspection systems
• Enforce strict quality standards of emission testing centers

• Enforce road (and lane) regulations in a strict and transparent manner
• Continue implementation and improvement of current vehicle reduction scheme
• Conduct comprehensive driver education

• Immediate deployment of AQ advertisement boards
• Public dissemination of AQ index and other monitoring results (e.g health impacts) through mass and print media
• Sustain ambient AQ monitoring program

• Strengthen institutional, technical, and management capacity of EMB, LGUs, and other allied agencies
• Strengthen existing tripartite partnership between government, private sector, and civil society
• Encourage science and policy research on air quality issues such as AQ standards, transboundary transport, etc.