1 Population and Air Quality in Metro Manila Marlon Viejo Master in Population Studies University of the Philippines Population Institute Introduction Among many large cities around the world, air pollution poses a grave threat to human and environmental health (Brennan 1996; Schneider 1998; WHO/UNEP 1992; World Resources Institute 1992). There are different types of compounds and chemicals known as air pollutants which are released into the atmosphere through different human activities. In 1992, a survey of the 20 world‟s largest megacities revealed that the World Health Organization (WHO) guidelines were exceeded by at least one of these pollutants in each megacity. These exceeding levels of air pollutants have been shown to produce negative impacts on respiratory, cardiovascular, and neurological systems among human populations. In the Philippines, epidemiological studies on the impact of air pollution on health have been conducted in Metro Manila in the 1990s. A study among drivers and commuters showed that the symptoms of Chronic Obstructive Pulmonary Disease (COPD) such as cough, phlegm, wheezing and shortness of breath were found to be more than twice prevalent among jeepney drivers as among commuters or air conditioned bus drivers (Subida and Torres 1991). In 1993, a study among school children and child vendors in Metro Manila revealed that child vendors were at greater risk of being exposed to air pollutants than other child groups, due to the roadside environment they work in, low socioeconomic status and the risks associated with it (Subida and Torres 1994). In a 1996 study among 630 infants in Metro Manila, it was reported that the cumulative incidences of acute lower respiratory infections (ALRI) and cough and colds were 81.5 per 1000 infants and 584.5 per 1000 infants respectively. The major risk factors identified to be significant in the development of ALRI among infants were PM 10 1 level indoors, absence of breastfeeding, and the number of smokers in the household of infants. In general, it was reported that particulate which can be inhaled are above the acceptable levels in Metro Manila (DOH 1996). Most research on air pollution tackles the sources rather than the causes of pollution. Through the monitoring of the Department of Environment and Natural Resources – Environmental Management Bureau (DENR-EMB), emissions of air pollutants are classified according to Area, Stationary and Mobile Sources which are roads, factories and gas-powered vehicles, respectively. The important sources of pollution vary from city to city. In Metro Manila, 2006 data showed that there are about 6 million registered vehicles plying its roads.