Air pollution driven by wildfires have been linked with a heightened risk of committing suicide in rural populations, according to new research in the US.
Every 10 per cent increase in particulate matter, or PM2.5, pollution in the rural counties was linked to a rise of 1.5 per cent in monthly suicide rates, the study from the University of Illinois Urbana-Champaign, Illinois, US, found.
There is now evidence linking air pollution, long known for its bad effects on physical health, with mental health problems such as anxiety, depression and suicide, according to David Molitor, a professor of finance at the university and co-author of the study published in the journal Proceedings of the National Academy of Sciences (PNAS).
For the study, the researchers used data on deaths by suicide and satellite-based measurements of wildfire smoke and PM2.5 concentrations in the US from 2007-19.
They then compared year-on-year monthly levels of smoke exposure at the county-level to changes in suicide rates, and then analysed these effects across local areas and demographic groups. A county is the largest administrative district within a US state.
The researchers associated worse air quality with higher rates of suicide, even as these trends were seen to emerge among only certain demographic groups in rural areas.
Higher suicide rates linked to PM pollution were concentrated among demographic groups with both a high baseline suicide risk and high exposure to outdoor air - rural white males of working age, and rural adults with no college education, the study said.
On the other hand, the researchers found no evidence linking wildfire smoke pollution to suicide risk in the urban population.
"Suicide rates were about 36 per cent higher in rural versus urban counties during our sample period. All of the effects seem to be concentrated in the rural populations," said Molitor.
However, demographic differences alone cannot fully explain the disproportionate impact of air quality in rural areas, the study said.
The study findings rather reflect broader regional influences, it said.
One such influence being that of individual exposure to air pollution.
For the same level of ambient air pollution, the study found personal exposures to vary by a factor of 20 between individuals depending on factors such as housing, investments and behaviour.
For example, individuals in rural counties spent significantly more time outdoors and were more likely to be employed in outdoor occupations.
Previous studies have found that rural populations, having lower average incomes compared to their urban counterparts, are also less likely to indulge in protective behaviours, like staying home on a day of heavy smoke, and make investments against smoke exposure.
These too could lead to variations in personal exposures, amounting to urban-rural differences, the study said.
"Most of the global population is regularly exposed to unhealthy levels of air pollution, and the emerging evidence suggests that this exposure is not only detrimental to physical health, but to mental health as well," said Molitor.