Air pollution can be defined as “the release of various gases, finely divided solids or finely dispersed liquid aerosols into the atmosphere at rates that exceed the natural capacity of the environment to dissipate and absorb them” (Nathanson, 2020). It continues to be a major concern worldwide with pollutants such as particulate matter (PM) and nitrogen dioxide (NO2) still being released into the atmosphere as a result of industrialization and urbanization. With a myriad of adverse health outcomes associated with exposure to air pollutants such as lung cancer and stroke, it is imperative to take steps to monitor and tackle air pollution and improve air quality especially in low and middle income countries.


Air pollution is said to be one of the major global causes of death. With about 91% of the world’s population living in places where air quality levels exceed the World Health Organisation (WHO) limits, an estimated 4.2 million deaths per year are attributed to ambient air pollution due to stroke, lung disease, lung cancer, acute and chronic respiratory illnesses (WHO, 2021). 

3.8 million premature deaths were also attributed to smoke exposure from cooking fires, especially in low and middle income countries (WHO, 2021) .  

Figure 1: Share of deaths from air pollution, 2017

Source: Our World In Data

There is currently a vast amount of epidemiological evidence that fine particulate matter (i.e. PM2.5) has various health effects on humans such as elevated hospitalizations, exacerbation of asthma, occurrence of lower respiratory symptoms and ultimately mortality (Pope III, 2000). Nitrogen Dioxide (NO2) and Ozone (O3) have also shown to contribute to risks of respiratory and circulatory mortality (Faustina et al., 2014, Turner et al., 2016).

Indoor vs Outdoor Air Pollution

Indoor air pollution has been a major cause of concern for many centuries now. It is said to be traced back to times when humans moved to areas with temperate climates and had to make fires for heating and cooking in their homes (Bruce et al., 2000). There was a heavy reliance on biomass fuels and the combustion of these fuels, which were mainly derived from wood, crop residue and animal dung, resulted in the production of smoke indoors which affected the health of household occupants. 

In many developed countries, advancements have been made from the use of biomass fuels to fossil fuels and electricity. In developing countries, however, biomass mass fuels are still widely used, especially among the poor as the more efficient fuel types tend to be more expensive (Piddock et al., 2014). 

While fuel combustion accounts for a proportion of indoor air pollution, other sources include tobacco smoking, indoor mould, building and furniture materials, consumer products such as cosmetics, perfumes etc (Figure 1).

Figure 2: Sources of Indoor Pollutants

Source: AndaTech Distribution, 2019

Outdoor pollution, also known as ambient air pollution, is the contamination of the ambient air as a result of the presence of chemical substances, gases and particulate matter (Almetwally et al., 2020). It has been in existence since humans started using fire for cooking and heating but industrialisation and urbanisation have increased it immensely. It occurs as a result of both natural and anthropogenic sources (WHO, 2021) but the effects of human activities have shown to outweigh that of natural sources of ambient air pollution. The main human activities that contribute greatly to ambient air pollution include fuel combustion from vehicles,  heat and power generation, residential cooking, heating and lighting, industrial activities and municipal and agricultural waste burning (WHO, 2021) . 

Figure 3: Sources of Outdoor Air Pollution

Source: Shan.Org 

Major Air Pollutants

1. Particulate Matter (PM): Particulate Matter (PM) is defined as the sum of liquid and solid particles that are suspended in the air, of which a majority are hazardous (Yavad & Devi, 2018). It is an important component of the atmosphere and a common indoor and outdoor pollutant. Vehicles, incinerators, dust, fires and industrial facilities are major contributors of PM in the environment (El Morabet, 2019). The particle sizes are between 2.5 mm (PM2.5) and 10 mm (PM10) and affect different parts of the respiratory system based on size.

2. Nitrogen Oxides (NOx): Nitrogen oxides (NOx) are a group of pollutant gases with stable oxides resulting from the reaction between nitrogen and oxygen (Sharma et al., 2013). They can be naturally created but are mainly produced by anthropogenic activities such as combustion of fossil fuels in vehicles and when generating power (Almetwally et al., 2020).

3. Carbon Monoxide (CO): Carbon monoxide (CO), a stable oxide of carbon, is produced from the partial oxidation of carbon containing compounds (Donald, 2016). It can be derived from both exogenous and endogenous sources. CO in the atmosphere is produced as a result of incomplete combustion in the process of coal power production, operation of vehicles and biomass burning (Varma et al., 2015). The most common source of CO endogenously is the degradation of heme by heme oxygenase (Varma et al., 2015).

4. Ozone (O3): Ozone is a colourless odourless gas which forms a protective layer against ultraviolet (UV) rays from the sun in the stratosphere, where it is harmless. In the troposphere however, it is a pollutant that could have various effects. Ozone in the troposphere is produced when nitrogen oxides from fossil fuel burning react with volatile organic compounds (Chen et al., 2007). This results in the release of oxygen atoms that combine with oxygen molecules to form ozone. Various respiratory symptoms such as coughing and dyspnea are associated with exposure to ozone.

5. Sulfur Dioxide (SO2): Sulfur dioxide (SO2) is a colourless acidic gas with a choking smell (Almetwally et al., 2020). It is widely used as fumigation for grains, a bleaching agent and in food preservation. It is released from natural sources such as volcanoes but can also be released as a result of anthropogenic activities such as burning of biomass and fossil fuels (Almetwally et al., 2020).

Table 1: Main Air Pollutants, their sources and maximum mean level recommended by WHO

Source: King et al., 2018

Health Effects of Air Pollution

Ambient and indoor air pollution have been recognized by the WHO as a risk factor for non-communicable diseases (WHO, 2019). When humans are exposed to high levels of air pollution, it results in adverse health outcomes, especially respiratory and cardiovascular diseases (Hoek et al., 2001, Franchini et al., 2012). While all components of air pollution are harmful to human health, particulate matter has been recognised to produce the most severe effects .

Majority of studies conducted have linked long-term exposure to air pollution with an increased risk of coronary artery disease (Gan et al., 2012, Pope et al., 2004 ). Studies have also shown a positive association between short-term exposure to gaseous components and PM with the risk of death from heart failure (Shah et al., 2013).

Chronic obstructive pulmonary disease, lung cancer, acute respiratory infections and respiratory allergies have all been linked to exposure to air pollutants (Brunekreef & Holgate, 2002). 

Asides from respiratory and cardiovascular  diseases, air pollution has also been linked to childhood leukemia, type 2 diabetes mellitus and bladder cancer (Schraufnagel et al., 2018). It has also been shown to be associated with osteoporosis, conjunctivitis, dry eye disease and inflammatory bowel disease (Schraufnagel et al., 2018).

Figure 4: Deaths linked to outdoor and household air pollution

Source: Climate and Clean Air Coalition

Air Pollution in Africa

The extent of air pollution in Africa has been difficult to quantify as most studies are carried out in developed countries and available studies are mainly of poor quality. There is also a lack of capacity to measure air quality in the majority of countries. A 2019 UNICEF report said only 7 out of the 54 African countries have real-time and reliable air pollution monitors (UNICEF, 2019).

A rapid growth in the population in addition to industrialisation and urbanisation, have had a major impact on air pollution in Africa and with most of the population on the continent living in extreme poverty, air pollution is a major problem. Some African countries such as Mali and Cote d’Ivoire have some of the highest air pollution indices globally (AQICN, 2021).

Major sources of air pollution in Africa include traffic emission, mining of natural resources, use of solid fuel for cooking, re-suspended dust from unpaved roads, waste incineration and bush burning, use of insecticides to control malaria and the Sahara desert, which is the highest source of atmospheric particulate matter in the world (Fayiga et al., 2018).

Deaths from outdoor pollution in Africa is said to have increased by 57% in about three decades, from 164,000 in 1990 to 258,000 in 2017 (UNICEF, 2019). A study conducted by researchers at NASA stated that air pollution accounts for about 780,000 premature deaths per year in Africa (Bauer et al., 2019). 

Air Pollution in Nigeria

Air pollution continues to be an unnoticed or overlooked problem in Nigeria. Many Nigerian urban cities suffer from high exposure to air pollutants, with the WHO ranking 4 Nigerian cities as some of the most polluted cities in 2016 (WHO, 2016) (Figure 5). Nigeria also happens to be the country with the highest number of premature deaths due to particulate matter pollution in the Sub-Saharan region (49,100) (IHME, 2020). A study conducted by the World Bank estimated that 11,200 premature deaths were as a result of air pollution in Lagos (Croitoru et al., 2020).

Figure 5: Cities with the worst air quality in the world

Source: WHO, 2016

Figure 6: Percentage of Household using solid fuel by LGA, Kaduna State

Source: Kaduna State General House Report, 2015

The heavy use of generators, kerosene stoves, firewood and coal for cooking and high levels of waste incineration are some of the contributing factors to high levels of PM in the atmosphere in Nigeria. The Nigerian Demographic and Health Survey conducted in 2013 showed that approximately 70% of households nationwide used solid fuels for cooking (National Population Commission, 2013). A survey conducted by the Kaduna state bureau of statistics in 2015 also showed that the majority of households in Kaduna use solid fuels for cooking (Figure 6). With such heavy use of solid fuels, in addition to other sources of air pollution, the Nigerian population is at an increased risk of developing cardiovascular and respiratory problems.

There is also a lack of adequate resources and equipment in the country to conduct air quality studies that would aid decision makers in creating policies to reduce the level of air pollution in the country.


The need for cleaner air globally is a continuous battle. There is however a need for immediate action to be taken in low and middle income countries like Nigeria to reduce mortality and morbidity attributed to air pollution as it is often overlooked currently. 

Research on air quality in Nigeria and Africa as a whole is of utmost importance in tackling air pollution on the continent. Also, with deliberate efforts being made by the government to transition to renewable and less toxic sources of energy, and policies being drafted by our lawmakers to support the fight against air pollution, we can move closer towards our goal for cleaner air. 


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