Protecting populations from the health harms of air pollution
BMJ 2023; 383 doi: https://doi.org/10.1136/bmj.p2020 (Published 04 October 2023) Cite this as: BMJ 2023;383:p2020Linked Research
Interactive effects of ambient fine particulate matter and ozone on daily mortality in 372 cities
- James Sullivan, medical student fellow,
- Cecilia Sorensen, director
- Global Consortium on Climate and Health Education, Mailman School of Public Health, Columbia University, New York, NY, USA
- Correspondence to: C Sorensen cjs2282{at}cumc.columbia.edu
The combustion of fossil fuel drives climate change by producing greenhouse gases, and it harms human health through air pollution, which is responsible for more than eight million deaths annually, accounting for nearly 15% of deaths worldwide.1
The linked study by Liu and colleagues (doi:10.1136/bmj-2023-075203) sheds new light on the pervasive harms of air pollution and exemplifies how climate change—and the human activities that drive it—multiply the risk of harm. These authors showed how two common air pollutants, fine particulate matter (PM2.5, airborne particles with a diameter of ≤2.5 µm) and ozone (O3), act synergistically to harm those exposed,2 providing compelling new evidence that both policies and healthcare practices must change to account for new and evolving understanding of the compound effects of climate change, its drivers, and its consequences on human health.
PM2.5 is generated primarily from the burning of fossil fuels and other industrial activities, and ground level O3 forms when byproducts of fossil fuel combustion react in sunlight and heat. These particles damage lung tissue when inhaled and eventually cross into the bloodstream where they cause or exacerbate systemic diseases through pro-inflammatory mechanisms, including cardiovascular disease, diabetes, obesity, preterm birth, pre-eclampsia, and cancer.3456789
Although evidence suggests that concomitant exposure to PM2.5 and O3 can lead to worse health outcomes, national and international organizations currently regulate each pollutant independently.21011 Using an international dataset of 372 cities across 19 countries and regions, Liu and colleagues found a statistically significant synergistic interaction between these two pollutants and prevalence of daily total, cardiovascular, and respiratory mortality. When PM2.5 and O3 were both present, mortality rates were greater than the additive effects of exposure to each pollutant alone.2
Given recent findings of synergy between common pollutants, a need is growing to account for these compounding harmful effects in emissions standards and regulations worldwide.101213 Even current composite measures, such as the Air Quality Index,14 provide different weights to individual pollutants but do not account for any interaction or non-linearity between pollutants. A shift to composite, multipollutant regulatory models that include non-linear coefficients or a mixture assessment factor have been called for by major organizations,11 regulators,15 and researchers16171819 and could address this limitation.
Such regulation is essential, as ongoing combustion of fossil fuel, coupled with hotter days (leading to more ground level O3) and increasingly common and severe wildfires, pose a serious threat to the universal right to health.202122 Furthermore, areas of socioeconomic disadvantage and those with a high prevalence of minority and other vulnerable groups are already disproportionately affected by poor air quality,20 and faster warming in these areas can exacerbate the inequity further through mechanisms such as increased localized O3 production.232425 Yet, regulatory standards still rely on geographic averages, rarely accounting for this unequal burden of exposure, let alone synergistic effects. Through the intersection of existing inequalities in health, structural racism, and other forms of discrimination, climate change therefore acts as a threat multiplier, exacerbating existing drivers of poor health for the world’s most vulnerable populations.26
Alongside the moral imperative to tackle health inequities, better regulation of air pollution can reduce healthcare costs by preventing harmful exposures.27 Much more stands to be gained, medically and financially, if the synergistic effects of PM2.5, O3, and likely other common pollutants are considered.
Equipping clinicians and patients with solutions
While policy wheels turn slowly, clinicians, patients, and populations urgently need to implement evidence based interventions to reduce personal risks from air pollution, such as refraining from strenuous outdoor exercise when air quality is poor, monitoring heat and air quality,28 staying indoors with high efficiency particulate air (HEPA) filtration systems, using N95 respirator masks, and more.2930 Clinicians and other healthcare professionals across specialties need to equip patients and communities with these protective physical, behavioral, technological, and pharmacological interventions 5 and identify patients at high risk owing to pre-existing respiratory and cardiovascular disease, age, pregnancy, low paid (or no) employment, and poor housing.31 Unfortunately, most healthcare professionals lack the knowledge and skills needed to recognize, prepare for, and respond to climate change related health and health system threats,32 because climate change is largely absent from professional training programmes.
As evidence emerges on risk multiplication, complexity, and disproportionate burden of harms, society must be ready to swiftly implement population level and individual approaches to protect human health. Regulators and policy makers must act on policies to reduce air pollution and drivers of climate change, while clinicians and patients need to drive mitigation and adaptation measures to reduce exposure risks in the community as we all face this planetary and human health crisis together.
Footnotes
Competing interests: The BMJ has judged that there are no disqualifying financial ties to commercial companies. The authors declare the following other interests: none.
Further details of The BMJ policy on financial interests is here: https://www.bmj.com/sites/default/files/attachments/resources/2016/03/16-current-bmj-education-coi-form.pdf.
Provenance and peer review: Commissioned; not externally peer reviewed.