# **1. Introduction**

## **1.1 Background**

Air pollution episodes are prevalent in cities and urban centers usually resulting from the cumulative anthropogenic alterations of the natural environmental systems, due to the inevitable and increasing demand for limited resources that often exceed the carrying capacity of cities (Gramsch et al., 2006; <mark>Martínez, 2015).</mark> According to WHO (2018), more than 80% of inhabitants in monitored urban centers are exposed to pollution levels that exceed WHO prescribed limits (Annex 1).

Consequently, populations in fast-growing urban centers are exposed to air pollution–linked health threats (WHO, 2018) with significant dependence on exposure periods. Broadly speaking, a 2018 WHO report indicates that 7 million people die every year from exposure to air pollution with the majority of deaths occurring in developing countries. WHO further ranks air pollution (i.e. both outdoor from industries, construction & automobiles, and indoor from solid fuel combustion) among the 24 leading risk factors for global mortality (WHO, 2009). A recent OECD (Economic Co-operation and Development Centre) study quantifying human and financial costs of Africa's outdoor air pollution found air pollution to be more deadly in Africa than malnutrition or dirty water; specifically, it estimates that air pollution in Africa kills 712,000 people a year prematurely, compared with approximately 542,000 from unsafe water, 275,000 from malnutrition and 391,000 from unsafe sanitation (OECD, 2016).

Findings from empirical epidemiological studies consistently show association of pollutant exposure and exacerbation of illnesses and increased mortality for cardiovascular and respiratory cases among vulnerable groups, e.g., older people, children, pregnant women, lower socioeconomic groupings in low-income countries, etc. (Seaton et al., 1995; <mark>Brunekreef & Holgate, 2002; B</mark> ellinger, 2005; <mark>Kampa & Castanas, 2008). Respectively, morbidity and mortality cases are largely linked to lung cancer, ischemic heart disease and stroke, Chronic Obstructive Pulmonary Disease (COPD), and respiratory infection. For example, a 9-year study (1990s) covering 38 million people in 8 European cities found a significant increase in hospital admissions for asthma and COPD, and Cardiovascular Disease (CVD) for people older than 65 years per 10μ</mark> gm<sup>-3</sup> <mark>exposure to PM</mark> 10 <mark>. More recently (2015), exposure to PM</mark> 2.5 <mark>caused 4.2 million deaths accounting for 7.6% recorded total global deaths thus making it the most important pollutant, and also ranked the 5th global risk factor in 2015. Additionally, O</mark> 3 <mark>accounted for over 0.25 million deaths (Atkinson et al., 2001; Cohen et al., 2017; WHO, 2018).</mark> A snapshot of historical pollution trends and projections in developed countries and the world’s megacities indicate higher per-capita emission levels than cities in low-income economies. However, this outlook is projected to be altered as air pollution has been increasingly severe in fast-expanding cities from non-industrialized countries often exceeding WHO limits (Mayer, 1999). Without any additional action to limit or control air pollution, challenges are only expected to increase as firms and people concentrate further in cities as economic growth rises (Bose, 2010; Kilroy et al., 2015; <mark>Martínez, 2015)</mark> .

Whereas strong regulatory regimes (e.g. restriction of lead and sulfur bearing fuels, strict emission limits, etc.) and technological advances have generally resulted in improved air quality in industrialized economies over time, e.g., China from 2013-2015 (Zheng et al., 2017), a broad plethora of literature and seminal studies still denote distributed pollution levels across a wide 2