The present consensus on how particulate air pollution (such as wood smoke from cooking fires, still commonplace in much of the world) causes an acceleration of age-related disease and mortality is that this is a matter of inflammation. Particules lodge in the lungs, and there spur chronic inflammation that drives onset and progression of all common age-related conditions. The evidence for this to be a causal relationship seems fairly compelling, based on studies of similar populations with different particulate exposure that rule out socioeconomic factors. It is certainly the case that more polluted regions are usually less wealthy regions, and it is certainly the case that wealth influences life expectancy, but wealth doesn’t appear to be the driving mechanism here.

A new analysis of 16 years of publicly accessible health data on 68.5 million Medicare enrollees provides broad evidence that long-term exposure to fine particles in the air – even at levels below current EPA standards – leads to increased mortality rates among the elderly. Based on the results of five complementary statistical models, including three causal inference methods, the researchers estimate that if the EPA had lowered the air quality standard for fine particle concentration from 12 μg/m3 down to the WHO guideline of 10 μg/m3, more than 140,000 lives might have been saved within one decade.

A number of studies have documented a strong correlation between long-term exposure to fine particulate and greater human mortality, but some concern has remained about the causal nature of the evidence, and whether it is sufficient to inform revisions to air quality standards. Some scientists argue that modern causal inference methods can provide such evidence, using the right data.

Analyzing a massive dataset through five distinct approaches, including two traditional statistical methods and three causal inference methods, researchers derived broad evidence consistent with a causal link between long-term particulate exposure and mortality. Modeling a 10 μg/m3 decrease of fine particle concentration between 2000 and 2016 resulted in a 6% to 7% decrease in mortality risk. Based on their model results, the researchers estimated that more than 140,000 lives might have been saved if the current U.S. standard for fine particle concentration had been lowered to 10 μg/m3 between 2007 and 2016.