Inequities in air pollution exposure and gaps in air quality monitoring

Abstract

Air pollution is the world’s single largest environmental health risk factor. It is responsible for an estimated 7 to 9 million deaths each year, of which more than 70% are due to noncommunicable diseases (NCDs).1Lelieveld J. Evans J.S. Fnais M. Giannadaki D. Pozzer A. The contribution of outdoor air pollution sources to premature mortality on a global scale.Nature. 2015; 525: 367-371Crossref PubMed Scopus (2772) Google Scholar,2Landrigan P.J. Fuller R. Acosta N.J. Adeyi O. Arnold R. Baldé A.B. et al.The Lancet Commission on Pollution and Health.Lancet. 2018; 391: 462-512Abstract Full Text Full Text PDF PubMed Scopus (1573) Google Scholar The death toll from air pollution is currently 3 times greater than that from malaria, HIV/AIDS, and tuberculosis combined.2Landrigan P.J. Fuller R. Acosta N.J. Adeyi O. Arnold R. Baldé A.B. et al.The Lancet Commission on Pollution and Health.Lancet. 2018; 391: 462-512Abstract Full Text Full Text PDF PubMed Scopus (1573) Google Scholar Numerous publications have covered the various air pollutants and their negative impacts on respiratory and cardiovascular health following both short-term and chronic exposures. Here, we highlight some of the current pressing issues and the actions needed to resolve them. Despite substantial improvements in air quality standards in many countries over recent decades, 92% of the world population remains exposed to unhealthy levels of air pollution. However, although air pollution is clearly a global problem, it disproportionately affects low- and middle-income countries (LMICs). Approximately 97% of cities with populations of more than 100,000 inhabitants do not meet World Health Organization air quality guidelines in LMICs compared with 49% in high-income countries (HICs). In addition to being affected by ambient air pollution, 3 billion people worldwide and 90% of rural households in LMICs are affected by indoor air pollution from the use of solid fuels for domestic cooking and heating. Compared with HICs, LMICs incur a higher proportion of disability-adjusted life years lost as a result of noncommunicable diseases attributable to air pollution and more than 90% of air pollution–related deaths.2Landrigan P.J. Fuller R. Acosta N.J. Adeyi O. Arnold R. Baldé A.B. et al.The Lancet Commission on Pollution and Health.Lancet. 2018; 391: 462-512Abstract Full Text Full Text PDF PubMed Scopus (1573) Google Scholar In most LMICs, this disease and mortality burden has increased significantly over recent decades as a result of increased levels of pollution along with a growing and ageing population.2Landrigan P.J. Fuller R. Acosta N.J. Adeyi O. Arnold R. Baldé A.B. et al.The Lancet Commission on Pollution and Health.Lancet. 2018; 391: 462-512Abstract Full Text Full Text PDF PubMed Scopus (1573) Google Scholar Yet, although LMICs experience the highest exposures and bear the brunt of the health burden, air quality monitoring and air pollution exposure research are often lacking in these countries.3Burns J. Boogaard H. Polus S. Pfadenhauer L.M. Rohwer A.C. Van Erp A.M. et al.Interventions to reduce ambient air pollution and their effects on health: an abridged Cochrane systematic review.Environ Int. 2020; 135105400Crossref PubMed Scopus (33) Google Scholar In Fig 1, we show the mean annual population-weighted mass concentration of particles less than 2.5 μm in size (PM2.5) by country, as well as the location of all existing PM2.5 ground monitors. With the exception of India and China, monitoring is sparse in LMICs and lacking in many of them. Africa in particular has various countries in which annual PM2.5 concentrations exceed the quality targets set in World Health Organization Interim Target-1, yet no monitoring is available. We also know that within-country socioeconomic and racial and ethnic disparities in air pollution exposures and health outcomes exist in both LMICs and HICs. In the United States, studies have shown that minorities and poorer communities tend to live in closer proximity to sources of pollution and are exposed to significantly higher concentrations of air pollutants.4Mikati I. Benson A.F. Luben T.J. Sacks J.D. Richmond-Bryant J. Disparities in distribution of particulate matter emission sources by race and poverty status.Am J Public Health. 2018; 108: 480-485Crossref PubMed Scopus (130) Google Scholar Furthermore, equivalent increases in PM2.5 values have been linked to significantly higher associations with adverse health outcomes in black and Hispanic populations than in white populations.4Mikati I. Benson A.F. Luben T.J. Sacks J.D. Richmond-Bryant J. Disparities in distribution of particulate matter emission sources by race and poverty status.Am J Public Health. 2018; 108: 480-485Crossref PubMed Scopus (130) Google Scholar These disparities are even more apparent in LMICs: a recent article published in the New York Times (https://www.nytimes.com/interactive/2020/12/17/world/asia/india-pollution-inequality.html) reported on the PM2.5 exposures experienced over the course of the day by 2 children in New Delhi, one of whom lived in a slum and the other of whom lived in one of the city’s upper middle class neighborhoods. The first child was consistently exposed to higher levels of pollution throughout the day, and his daily exposure was approximately 4 times higher than that of the upper middle class child. This higher exposure to air pollution, if chronic, could result in 5 additional potential years of life lost. Effectively improving air quality and mitigating the increasing burden of air pollution necessitates a multipronged approach, including research to inform policy, better monitoring, and setting-specific interventions. Although we now have an understanding of many of the respiratory and cardiovascular effects of air pollution, further research is needed to address existing gaps in knowledge on issues such as the long-term effects of exposure,5Tonne C. A call for epidemiology where the air pollution is.Lancet Planet Health. 2017; 1: e355-e356Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar the relative toxicity of pollutants from different sources,1Lelieveld J. Evans J.S. Fnais M. Giannadaki D. Pozzer A. The contribution of outdoor air pollution sources to premature mortality on a global scale.Nature. 2015; 525: 367-371Crossref PubMed Scopus (2772) Google Scholar and the adverse impacts of pollutants on cognitive development. Other remaining challenges include characterizing the joint and independent effects of multipollutant exposures, the concentrations and health risks of ultrafine particulate matter,6Schraufnagel D.E. The health effects of ultrafine particles.Exp Mol Med. 2020; 52: 311-317Crossref PubMed Scopus (149) Google Scholar and the effects of primary versus secondary particulate matter. The most pressing issue, however, is the need for bigger research efforts in LMICs, in which exposures are highest yet data are limited.7Prabhakaran P. Jaganathan S. Walia G.K. Wellenius G.A. Mandal S. Kumar K. et al.Building capacity for air pollution epidemiology in India.Environ Epidemiol. 2020; 4: 3117Crossref Google Scholar Gaps in knowledge include the apportionment of different sources and how these vary among urban, periurban, and rural environments. In addition, although household air pollution trials in LMICs have demonstrated drastic reductions in exposure with the use of fuels cleaner than biomass, the health effects of such interventions remain uncertain.8Mortimer K. Balmes J.R. Cookstove trials and tribulations: what is needed to decrease the burden of household air pollution?.Ann Am Thorac Soc. 2018; 15: 539-541Crossref PubMed Scopus (20) Google Scholar To determine accurate exposure-response relationships and inform intervention strategies, more ground-level monitoring is required, particularly in LMICs, in which monitoring stations are few and far between (Fig 1). Where ground measurements are lacking, satellite data and chemical transport models can be adopted to estimate pollutant concentrations. Recent years have also seen a rapid development in low-cost air quality sensors, which could be utilized to supplement the data from available monitoring stations. However, it is important that these devices undergo appropriate quality control and validation to verify their performance and precision. Ultimately, the use of regulations and legislation, as well as research into the effectiveness of interventions, are key in reducing exposures. However, there are also individual-level strategies that can be adopted to minimize personal exposures. Limiting physical activity outdoors on days with high pollution, minimizing near-road exposure, and reducing outdoor air infiltration indoors can reduce exposure to ambient air pollutants. Strategies to lower indoor air pollution include avoiding the use of solid fuels, ventilating and isolating cooking areas, and using high-efficiency particulate air filters.9Carlsten C. Salvi S. Wong G.W. Chung K.F. Personal strategies to minimise effects of air pollution on respiratory health: advice for providers, patients and the public.Eur Respir J. 2020; 551902056Crossref PubMed Scopus (29) Google Scholar Readily available air quality data for the general public and public information campaigns to raise awareness of the effects of air pollution and provide guidance on personal mitigation strategies would help facilitate and increase adoption of these practices. At a policy level, a move to cleaner fuels and measures to cut energy consumption are necessary for bringing both ambient and indoor air pollution down to safe levels. It is especially important for measures to be implemented in areas where few or none exist. Although a number of interventions to reduce ambient air pollution have been implemented, evidence of their effectiveness is mixed, pointing to the need for improved study design and analysis methods, as well as for more uniform evaluations.3Burns J. Boogaard H. Polus S. Pfadenhauer L.M. Rohwer A.C. Van Erp A.M. et al.Interventions to reduce ambient air pollution and their effects on health: an abridged Cochrane systematic review.Environ Int. 2020; 135105400Crossref PubMed Scopus (33) Google Scholar From a policy perspective, the specific choice of intervention needs to be context and setting specific and may require a combination of measures in cases in which multiple sources rather than a single source contribute heavily to the air pollution. Successful interventions to mitigate household air pollution require a multifaceted approach that involves not only affordable clean fuel but also education and behavioral messaging to bring about change in cultural views and cooking behaviors and promote exclusive use of clean fuel.10Checkley W, Williams KN, Kephart JL, Fandiño-Del-Rio M, Steenland NK, Gonzales GF et al. Effects of a cleaner energy intervention on cardiopulmonary outcomes in Peru: a randomized controlled trial. Am J Respir Crit Care Med https://doi.org/10.1164/rccm.202006-2319OC. Accessed December 11, 2020.Google Scholar Despite the extensive body of scientific evidence linking air pollution with increased morbidity and mortality, air pollution has only recently begun receiving public and policy attention, and mitigation strategies remain largely absent from guidelines on disease prevention. In a landmark ruling in 2020 that attracted global media attention, air pollution was recorded as a cause of death for a British girl who died in 2013 following an asthma attack, marking the first instance of air pollution being explicitly linked to a specific person’s death (https://www.bbc.com/news/uk-england-london-55330945#:∼:text=A%20nine%2Dyear%2Dold%20girl,east%20London%2C%20died%20in%202013). The 9-year old, who was black, lived in Lewisham in southeast London, within 25 meters of a major circular road along which she used to walk to get to school. A 2018 report highlighted the fact that levels of air pollution at a monitoring station within a mile of her home had consistently exceeded European Union legal limits and World Health Organization guidelines. This case raised questions about the government’s commitment to tackling air pollution and shined a light on the disparities faced by minorities and disadvantaged communities. We hope that this case encourages policymakers, not just in the United Kingdom but worldwide, to do more to meet air quality standards. It is important to note that strategies to mitigate air pollution are relevant not only to improving public health but also to combating climate change, and that the health and economic benefits associated with reducing air pollution far exceed the costs. In summary, air pollution remains one of the most important risk factors for illness and death worldwide. Although air pollution data have become more available worldwide and resources such as www.openaq.org have increased access to information, we do not prioritize air quality monitoring and research in the resource-poor settings in which air pollution–related disease burden is the highest, driving further inequities in health. A setting-specific multifaceted approach to target air pollution is needed to meet air quality standards and improve health around the world.