Background

 Air pollution is the presence of a heterogeneous mixture of compounds such as ground level ozone (O3), carbon monoxide (CO), sulphur dioxide (SO2), nitrogen oxides (NOx) and particulate matter (PM10 & PM2.5). These chemicals or compounds are released into the air in a quantity that is detrimental to the environment, animals and human beings as a whole. The World Health Organization (WHO) suggests that the pollution (indoor and outdoor) of the air we breathe is probably the most significant environmental problem that we are facing today and in most instances human activity such as inefficient modes of transport, household fuel and waste burning, coal-fired power plants, and industrial activities  \cite{who2018a} . However, there are also natural causes of air pollution such as volcano eruption and wildfires but their occurrence is rare and its effect is often localized as compared to the effects caused by pollution from human activity \cite{epc2017}.  Recently, a new model on air quality deisgned by the World Health Organization  (WHO) estimates that 92% of the world's population live in areas that exceed the WHO air quality limits.
    Most of the countries in the Western Pacific Region are developing nations that are experiencing the intense process of urbanization and industrial development, hence, the burden of air pollution related health effects is the largest\cite{Mannucci_2017}.
 
Exposure to air pollutants can affect human health in various ways, leading to increased mortality and morbidity and in most cases a shortend life expectancy. Recent studies have shown that there is growing and evolving epidemiological evidence on the health effects  of ambient air pollution\cite{usepa2009}. The World Health Organization stated that outdoor (ambient) air pollution is a major environmental health problem that is responsible for some  72% premature deaths worldwide. In 2012, it was estimated that 3 million premature deaths from cardiovascular, respiratory disease and cancers throughout the world were caused by ambient air pollution and in particular exposure to particulate matter of 10 microns (PM10) or less  \cite{who2016}. From these premature deaths 87% were from low- and middle-income countries with the greatest burden being in those countries in the WHO Western Pacific and South-East Asia regions.
Health effects of ambient air pollution ranges from increased hospital admissions and emergency rooms visits to increase risk of premature death\cite{who2018}
The World Health Organization ranks particulate air pollution as the 13th leading cause of mortality worldwide and recent studies have shown a deeper and more complicated relationship.