Air pollution is defined as the contamination of indoor or outdoor environments by any chemical, physical, or biological agent that modifies the natural characteristics of the atmosphere (WHO, 2022). Air pollution can result from natural sources (e.g. dust, fires or volcanic eruptions) or human activities (e.g. motor vehicles and industrial facilities). This Toolkit page includes reviews of exposures to air pollution from both natural and human sources. Interventions for reducing air pollution and promoting health are summarised in another Toolkit page.
The most commonly examined air pollutant was particulate matter (PM) (n=16), which is categorized by the size of particles. PM10 (n=14) and PM2.5 (n=15), also known as “fine particles”, have diameters less than 10μm and 2.5μm respectively. Other commonly studied pollutants were nitric oxides (NOx; n=12), ozone (O3; n=8), and sulphur dioxide (SO2; n=7). Other air pollutants included carbon monoxide (CO), carbon dioxide (CO2), black smoke, biomass smoke, environmental tobacco smoke (also known as passive smoke), synthetic gasses, hydrocarbons and dust. Some studies specifically referred to traffic-related air pollution; others used proxies of air pollution (e.g. volume of heavy goods vehicles (Rugel 2020), proximity to industry or major roadways (Wray 2018); and the use of household fuels (Zhang 2007).
Twenty-one reviews examined the health impacts of air pollution from over 600 primary studies. Overall, exposure to air pollution had negative consequences on the respiratory, immune and cardiovascular systems, cancer, maternal health and birth outcomes, type 2 diabetes mellitus, weight, neurological diseases, mental health and death.
Most reviews considered all age groups or did not specify age, with one review focusing on older adults (Barnett 2018) and two reviews in children (Choo 2015; DePriest 2017). The reviews included studies from high-, middle- and low-income countries, with some reviews focusing specifically on sub-Saharan Africa (Alaazi 2020; Coker 2018), West Africa (De Longueville 2010), Brazil (Oliveira 2011), China (Zhang 2007; Zhang 2014), and Malaysia (Choo 2015).
Exposure to air pollution was associated with 56 negative health outcomes across 16 disease categories (Figure 1). Most reviews reported an association between air pollution exposure and respiratory disease or mortality. Other commonly reported associations with air pollution were diseases of the circulatory system (n=7), cancer (n=5), and mental health disorders (n=5).
For mortality outcomes, exposure to air pollution was associated with premature death (Arantes 2019; Ali 2019), cardiovascular mortality (Brunekreef 2005), respiratory mortality (Oliveira 2011; Alaazi 2020) and non-specified mortality (Brunekreef 2005; Rugel 2020; Ali 2019; Coker 2018; Hesterberg 2009; Rojas-Rueda 2021).
For mental health outcomes, exposure to air pollution was associated with:
- depression (Barnett 2018; Bernardini 2020; Coker 2018; Rojas-Rueda 2021; Sampson 2020);
- schizophrenia (Bernardini 2020; Rojas-Rueda 2021);
- panic attacks, substance abuse disorders, and suicide attempts (Bernardini 2020);
- dementia, autism, and attention-deficit/hyperactivity disorder (Rojas-Rueda 2021).
For physical health outcomes, exposure to air pollution was linked to:
- issues with the respiratory system (Rojas-Rueda 2021; Zhang 2007; Zhang 2014; Ali 2019; Arantes 2019; Brunekreef 2005; Coker 2018; Hesterberg 2009; Kurt 2016; Oliveira 2011; Choo 2015; De Longueville 2010), including
- cardiovascular disease (Ali 2019; Brunekreef 2005; Rugel 2020; De Longueville 2010), including
- adverse maternal health and birth outcomes, including
- type 2 diabetes mellitus (Dendup 2018; Rojas-Rueda 2021) and body weight status (An 2018; Rojas-Rueda 2021);
- problems with the immune system (Arantes 2019), including eye (Alaazi 2020) and ear (Rojas-Rueda 2021) infections;
- cancers, including cancer of the mouth, pharynx, larynx, breast, cervix and leukaemias (Rojas-Rueda 2021); lungs (Zhang 2007; Kurt 2016; Ali 2019; Rojas-Rueda 2021; Wray 2018); oesophagus (Zhang 2007; Rojas-Rueda 2021); and head and neck (Zhang 2007).
- neurological diseases, including Alzheimer’s and Parkinson’s disease (Rojas-Rueda 2021).
All reviews found that the exposure to air pollution had a strong negative impact on health. Despite the effects not all being statistically significant, as there was only one review with a meta-analysis (Barnett 2018), exposures to air pollution were associated with signficiant adverse events including death.
Efforts should be made to reduce exposure to air pollution. Recommendations included:
- develop air monitoring networks; these will facilitate epidemiological studies and if made publicly available, could enable stakeholders (including the general public) to monitor air pollution levels in their area and make decisions accordingly (Coker 2018)
- improve individualised data on air pollution exposure by increasing access and affordability of wearable technology, which may be a solution to improve personalised data collection and inform health practices (Wray 2018)
- cooperation at a multi-national level involving multiple stakeholders, including the government, industry, energy companies and the public (Kurt 2016)
- implementation of policies to reduce air pollution exposure at schools (e.g. restricting traffic in the vicinity of schools) and in homes, taking into consideration the health of individuals and the areas where such buildings are built (DePriest 2017)
- medical staff should consider the physical and social neighbourhood environment, including exposure to air pollution, when assessing children and others with asthma (DePriest 2017)
- invest in interventions to reduce air pollution and the harmful effects on health
One review reported on the high economic costs of health impacts from air pollution (Zhang 2014). Between 2002 and 2009, Lanzhou, China had economic losses of over a billion renminbi (RMB) (approx £120 million GBP) in most years, with the highest loss of 1.66 billion RMB (almost £200 million GBP) in 2009. The other 20 reviews did not report any direct information on the cost or resource implications of air pollution and health.
Quality of the evidence
Four reviews (19%) used tools to assess the risk of bias or quality, which had moderate (An 2018; Barnett 2018; Dendup 2018) and very low (Rugel 2020) quality evidence. The majority (81%) reviews were therefore ranked uncertain, giving the overall score of uncertain evidence. To improve the evidence base, future research should
- focus on at-risk or vulnerable and disadvantaged populations
- account for individual and other environmental factors by using more robust study designs
- develop standard definitions, methods, and measures for air pollutants and health outcomes (e.g. ICD-10 codes) to reduce heterogeneity and increase the ability to estimate pooled effects in meta-analyses
Searches for evidence were conducted between 2002 and 2020 in a median of three databases (IQR: 2-4). Ten of the included studies were formal systematic reviews (one with a meta-analysis (Barnett 2018), eight narrative/literature reviews, one umbrella review, one scoping review, and one integrative literature review.
External links to related sources
- WHO (2010): WHO Guidelines for indoor air quality: selected pollutants
- WHO (2014): WHO Guidelines for indoor air quality: Household fuel combustion
- WHO (2021): Ambient (outdoor) air pollution
- WHO (2021): Household air pollution and health
- WHO (2021): WHO global air quality guidelines
- WHO (2022): News release – billions of people still breathe unhealthy air
- IQAir (2021): Interactive global map of 2021 PM2.5 concentrations by city
- Global Carbon Project (Accessed 2022): Global Carbon Atlas
- OECD: Air pollution effects
- UK Government: Clean Air Strategy 2019
- UK Department for Environment, Food & Rural Affairs (2018): Air quality – explaining air pollution – at a glance
- Healthy Air (2022): Clean Air Consultation Tool
- Clean Air Fund (2022): The Pathyway to Healthy Air in the UK
References of included reviews
Alaazi, Dominic A., and Gamel A. M. Aganah. 2020. “Understanding the Slum-Health Conundrum in Sub-Saharan Africa: A Proposal for a Rights-Based Approach to Health Promotion in Slums.” Global Health Promotion 27 (3): 65–72.
Ali, Muhammad Ubaid, Guijian Liu, Balal Yousaf, Habib Ullah, Qumber Abbas, and Mehr Ahmad Mujtaba Munir. 2019. “A Systematic Review on Global Pollution Status of Particulate Matter-Associated Potential Toxic Elements and Health Perspectives in Urban Environment.” Environmental Geochemistry and Health 41 (3): 1131–62.
An, Ruopeng, Mengmeng Ji, Hai Yan, and Chenghua Guan. 2018. “Impact of Ambient Air Pollution on Obesity: A Systematic Review.” International Journal of Obesity 42 (6): 1112–26.
Arantes, B. L., T. Mauad, and D. F. Da Silva Filho. 2019. “Urban Forests, Air Quality and Health: A Systematic Review.” International Forestry Review 21 (2): 167–81.
Barnett, Anthony, Casper J. P. Zhang, Janice M. Johnston, and Ester Cerin. 2018. “Relationships between the Neighborhood Environment and Depression in Older Adults: A Systematic Review and Meta-Analysis.” International Psychogeriatrics / IPA 30 (8): 1153–76.
Bernardini, Francesco, Riccardo Trezzi, Roberto Quartesan, and Luigi Attademo. 2020. “Air Pollutants and Daily Hospital Admissions for Psychiatric Care: A Review.” Psychiatric Services 71 (12): 1270–76.
Brunekreef, B., and B. Forsberg. 2005. “Epidemiological Evidence of Effects of Coarse Airborne Particles on Health.” The European Respiratory Journal: Official Journal of the European Society for Clinical Respiratory Physiology 26 (2): 309–18.
Choo, Chua Poh, and Juliana Jalaludin. 2015. “An Overview of Indoor Air Quality and Its Impact on Respiratory Health among Malaysian School-Aged Children.” Reviews on Environmental Health 30 (1): 9–18.
Coker, Eric, and Samuel Kizito. 2018. “A Narrative Review on the Human Health Effects of Ambient Air Pollution in Sub-Saharan Africa: An Urgent Need for Health Effects Studies.” International Journal of Environmental Research and Public Health 15 (3). https://doi.org/10.3390/ijerph15030427.
De Longueville, Florence, Yvon-Carmen Hountondji, Sabine Henry, and Pierre Ozer. 2010. “What Do We Know about Effects of Desert Dust on Air Quality and Human Health in West Africa Compared to Other Regions?” The Science of the Total Environment 409 (1): 1–8.
Dendup, Tashi, Xiaoqi Feng, Stephanie Clingan, and Thomas Astell-Burt. 2018. “Environmental Risk Factors for Developing Type 2 Diabetes Mellitus: A Systematic Review.” International Journal of Environmental Research and Public Health 15 (1). https://doi.org/10.3390/ijerph15010078.
DePriest, Kelli, and Arlene Butz. 2017. “Neighborhood-Level Factors Related to Asthma in Children Living in Urban Areas.” The Journal of School Nursing: The Official Publication of the National Association of School Nurses 33 (1): 8–17.
Hesterberg, Thomas W., William B. Bunn, Roger O. McClellan, Ali K. Hamade, Christopher M. Long, and Peter A. Valberg. 2009. “Critical Review of the Human Data on Short-Term Nitrogen Dioxide (NO2) Exposures: Evidence for NO2 No-Effect Levels.” Critical Reviews in Toxicology 39 (9): 743–81.
Kurt, Ozlem Kar, Jingjing Zhang, and Kent E. Pinkerton. 2016. “Pulmonary Health Effects of Air Pollution.” Current Opinion in Pulmonary Medicine 22 (2): 138–43.
Oliveira, Beatriz Fátima Alves de, Eliane Ignotti, and Sandra S. Hacon. 2011. “A Systematic Review of the Physical and Chemical Characteristics of Pollutants from Biomass Burning and Combustion of Fossil Fuels and Health Effects in Brazil.” Cadernos de Saude Publica 27 (9): 1678–98.
Rojas-Rueda, David, Emily Morales-Zamora, Wael Abdullah Alsufyani, Christopher H. Herbst, Salem M. AlBalawi, Reem Alsukait, and Mashael Alomran. 2021. “Environmental Risk Factors and Health: An Umbrella Review of Meta-Analyses.” International Journal of Environmental Research and Public Health 18 (2). https://doi.org/10.3390/ijerph18020704.
Rugel, Emily Jessica, and Michael Brauer. 2020. “Quiet, Clean, Green, and Active: A Navigation Guide Systematic Review of the Impacts of Spatially Correlated Urban Exposures on a Range of Physical Health Outcomes.” Environmental Research 185 (June): 109388.
Sampson, Laura, Catherine K. Ettman, and Sandro Galea. 2020. “Urbanization, Urbanicity, and Depression: A Review of the Recent Global Literature.” Current Opinion in Psychiatry 33 (3): 233–44.
Wray, Alexander, Dana Lee Olstad, and Leia Michelle Minaker. 2018. “Smart Prevention: A New Approach to Primary and Secondary Cancer Prevention in Smart and Connected Communities.” Cities 79 (September): 53–69.
Zhang, J. J., and Smith, K.R. 2007. “Household Air Pollution from Coal and Biomass Fuels in China: Measurements, Health Impacts, and Interventions.” Environmental Health Perspectives 115 (6): 848–55.
Zhang, Yaqun, Min Li, Mercedes A. Bravo, Lan Jin, Amruta Nori-Sarma, Yanwen Xu, Donghong Guan, et al. 2014. “Air Quality in Lanzhou, a Major Industrial City in China: Characteristics of Air Pollution and Review of Existing Evidence from Air Pollution and Health Studies.” Water, Air, and Soil Pollution 225 (10). https://doi.org/10.1007/s11270-014-2187-3.