Exposure to low concentrations of air pollution, even amounts permitted under government regulations, may still kill tens of thousands of people a year.
Researchers studied the effects of levels of pollution permitted under American laws – and found they still caused deaths among the elderly.
The research was published in The Lancet Planetary Health.
Lead study author Mahdieh Danesh Yazdi, a postdoctoral fellow in Harvard Chan School's Department of Environmental Health, said: "We found that among elderly patients enrolled in [U.S. national health-insurance programme] Medicare, small increases in long-term exposure to both particle and gaseous air pollutants increased the risk of death, even at levels deemed safe by current regulations.
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"Our findings suggest that current air pollution limits are not adequate to protect the health of vulnerable groups."
The analysis included data on millions of Medicare enrollees from 2000 to 2016. The researchers predicted people's exposure levels by using satellite-based measurements, land-use data, meteorological data and chemical-transport models.
The study looked at the effects of three different types of pollutants: fine particulate matter, or PM2.5 – particulates with a diameter of less than 2.5 micrograms per cubic metre of air – nitrogen dioxide (NO2), and summer ozone (O3).
All three pollutants increased mortality risk among the participants.
Thousands of deaths could be attributed to even small increases in annual air pollution concentrations, according to the researchers.
Men were at greater risk of death from PM2.5 and O3, and people who identified as Black had a higher risk of death caused by NO2 and O3.
The study also found an increased risk of death for people living in lower-income areas.
Joel Schwartz, professor of environmental epidemiology and senior author of the study, said: "Our finding that people living in lower income areas are more susceptible to the harmful effects of air pollution means they are suffering a double whammy – more exposure, and greater risk from that exposure.”
A study released this year analysed the health effects of air pollution (and where it was coming from) in 200 countries.
The researchers said pollution from cars and industry is only part of the problem, as PM2.5 – tiny particles that can go into people’s lungs – can make people ill if they cook every night on a stove.
Professor Randall Martin of Washington University in St Louis, US, said: "PM2.5 is the world's leading environmental risk factor for mortality. Our key objective is to understand its sources.”
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