What's the Most Harmful Particulate Matter?

A new study from the University of California San Diego (UCSD) has revealed that particulate matter (PM) pollution caused by wildfires could be significantly worse for human health than that generated by other sources, such as tailpipe emissions. Although that conclusion has already been arrived at during several lab-based studies, this is the first to deliver the same verdict in a real-world setting.

The implications of the discovery are that regulatory bodies such as the Environmental Protection Agency (EPA) should factor in the source of PM pollution when defining “safe” limits for concentrations of the contaminant. That kind of distinction is particularly important in California where the research was conducted, due to the high incidence of wildfires and the state’s swelling populations in coastal regions.

Alarming results

The paper was written by researchers from Scripps Institution of Oceanography, in collaboration with scientists at the Herbert Wertheim School of Public Health and Human Longevity Science at UCSD. To arrive at their findings, they analysed particulate matter sensing records and hospital admissions data over a 14-year period, correlating the latter with the former.

In order to differentiate between PM particles produced by wildfire and those from other sources, the researchers defined the wildfire pollution as that experienced by people exposed to Santa Ana winds when there was fire upwind. They also used data from the National Oceanic and Atmospheric Administration (NOAA) to identify smoke plumes as a secondary measure of a person’s exposure.

They found that a jump in the concentration in ambient air of 10μg/m3 of non-wildfire smoke increased the likelihood of a person being admitted to hospital for cardiovascular or respiratory ailments by 1%. However, when that pollution was found to have emanated from wildfires, the risk leapt up by anywhere between 1.3% and 10%, representing a sizable increase.

Reassessing the regulations

Given that our capacity to monitor levels of black carbon and PMx is greater than ever before, the scientists behind the paper argue that the EPA and other environmental authorities must factor the source of PM into their calculations when decreeing legal limits. Indeed, assuming that all PM particles are equally toxic appears to be inaccurate, so regulating them as if they were is misguided at best and outright dangerous at worst.

It’s already well known that PM2.5 particles – which have a diameter 20 times smaller than a human hair and can be easily inhaled into the body – can wreak serious damage upon our internal organs. Now, it appears that PM2.5 can be even more destructive if it’s created during the combustion of forested areas, although the exact reasons behind the discrepancy are not understood.

“As conditions in Southern California become hotter and drier, we expect to see increased wildfire activity,” explains Tom Corringham, co-author on the research. “This study demonstrates that the harm due to wildfire smoke may be greater than previously thought, bolstering the argument for early wildfire detection systems and efforts to mitigate climate change.”