Outdoor air pollution is a major environmental health risk affecting everyone in developed and developing countries alike . Recently, a new model on air quality designed by the World Health Organization (WHO) estimates that 92% of the world's population live in areas that exceed the WHO air quality limits. 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 from human activities 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 air pollution from human activity \cite{epc2017}.
The common cause of ambient air pollution are emissions caused by combustion processes from motor vehicles, solid fuel burning and industry. Most of these emissions contain a heterogeneous mixture of pollutants such as particulate matter, ground-level ozone, carbon monoxide, lead, sulphur oxides, nitrogen oxides and is of great concern because of their effects to the environment, animals and humans. These pollutants have been classified by the USEPA as criteria pollutants because their source of emissions is diverse and widespread, therefore, guidelines have been established to regulate their permissible levels.
The harmful effects of ambient air pollution on human health have been consistently documented by many epidemiological studies worldwide, and it has been calculated that globally at least seven million deaths are annually attributable to the effects of air pollution\cite{Mannucci_2017}. The World Health Organization ranks air pollution as the 13th leading cause of mortality worldwide and recent studies have shown a deeper and more complicated relationship. Exposure to air pollutants can affect human health in various ways, leading to increased mortality and morbidity and in most cases a shortened life expectancy. Health effects of ambient air pollution ranges from increased hospital admissions and emergency rooms visits to increase risk of premature death\cite{who2018}. 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 suggests that outdoor ambient air pollution is responsible for some 72% premature deaths worldwide and in 2012, it was estimated that 3 million premature deaths from cardiovascular, respiratory disease and cancers in cities and rural areas 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.
Most of the countries in the Western Pacific Region are developing nations that are experiencing an intense process of urbanization and industrial development, hence, the burden of air pollution-related health effects is large \cite{Mannucci_2017}. WHO estimates that about 3 billion people in developing nations rely on firewood and charcoal for cooking and other domestic uses, hence, they are continuously exposed to smoke-induced illnesses especially amongst children and the elderly. The latest burden estimates reflect the very significant role air pollution plays in cardiovascular illness and premature deaths – much more so than was previously understood by scientists.