PM and health effects

Our research on PM and health outcomes has turned up two findings: 1) On a mass basis, the health effects of PM 0.1 and PM 2.5 are generally the same, or rather that 0.1 is not significantly worse on health than 2.5 & 2) the research on ultrafine PM 0.1 is lacking and its impact on health outcomes isn’t well understood.

Question: Is there a significant difference in health effects between PM 2.5 and PM 0.1 on a mass basis? Does the composition of particulate matter affect health outcomes in different ways? Is this an area that is generally understood and supported by evidence?

Hi @kchance , @bontempi , @Cerruti , @hopkepk , @avidela , @djaffe
You might be able to help us answer this question. What do you think are the biggest challenges?

@jamesburbridge, @TerryMulligan
There is the issue of the heterogeneity of UFP exposures and the metric. Most UFP (particle number concentrations for sizes <100 nm) have used a central monitor and not found a lot of clear results. We do see effects on MIs with a changing toxicity with time. See Wang et al. Environmental Health (2019) 18:82

Hi @sagnikdey , @yusef , @yousotchik , @Sierramtz , @Dwalsh11 . @alanDRI , @mccubbin
Join the discussion to provide your views on how PM size affects health.

Great comment @hopkepk! Thank you.

Hi @omehrpour, @mskoehle, @rgschreib, @ckellogg
We’d love to see any input that you might have on this issue. Join the discussion.

I agree with @hopkepk the ability to adequately assess UFPs in health studies is a limiting factor. A study done in Netherlands that used mobile monitoring to assess UFPs found higher impacts of UFPs than PM2.5.

The issue of comparison with PM2.5 on a mass basis is problematic, mainly because UFPs are often measured by particle number rather than mass.

From a toxicological perspective UFP’s present an added pathway for adverse health effects, where they are able to penetrate human physiological barriers and end up in the brain, placenta etc with the potential of causing direct impacts.

Additionally UFPs maybe generated from different sources than PM2.5.

Back in the latter part of the 90s, the US EPA issued its first major cost/benefit analysis. While there were several flaws in this analysis, one of the major findings was that 80% of the benefits came from reductions in particulates emissions. This analysis looked at the 6 criteria pollutants…Particulates, SO2, NOx, CO, lead, and ozone. In the US, ambient air quality had improved dramatically and most of the country was in attainment relative to ambient air standards for particulates, SO2, NOx, CO, and lead. Ozone has some special issues and is influenced by automobile emissions and proximity to large bodies of water. As a result, EPA declared SO2 and NOx as precursors to particulate formation. These compounds end up as sulfate and nitrate particulates that are washed out of the atmosphere in rain (ie acid rain). As a result, emissions of all criteria pollutants are down by nearly 80% since 1970, while the economy is up by a factor of 3. Even so, the benefits are somewhat difficult to conclusively pin down. You would be hard pressed to find a death certificate that says somebody died from particulates. There have been very, very few studies that have been able to do a true, side by side comparison simply because we cannot do a controlled study on what would have happened had we not done such a good job in the US of reducing emissions. The best study that I have ever seen was done by Prof, Michael Greenstone when he was at MIT. He used infant mortality data (which is very detailed) from the period before and after the 1978 modifications to the Clean Air Act. These regulations stipulated the first attainment/non attainment areas for particulates. By selecting regions of the country with approximately the same economic conditions but were in different attainment/non attainment areas, he was able to statistically tease out the impact of particulate emissions on infant mortality, while correcting for such potential influences as smoking/non smoking, alcoholism, income, etc. The results showed a modest impact of 1000 infant deaths out of 2 million births. Since infants have the same mortality rate in the first year of life as the population as a whole, this gives some indication of the level of impact of particulate emissions. The death rate in the US is on the order of 2 million people each year, so the number of deaths attributable to air pollution in the US is somewhat exaggerated. Of course, in places like China and Southeast Asia, the ambient concentrations are much higher and will lead to higher mortality rates.

As mentioned above, fine particulates (<PM 2.5) get into your lungs and get trapped there. Larger particulates (PM 10) tend to get washed out from the atmosphere (think rocks). Recognize that a PM 10 particle weighs over 13 times as much as a PM 2.5 particle. The ratio gets worse (ie larger) for particles greater than PM 10 compared to particles smaller than PM 2.5. Thus, the weight of the particles, by itself, may not be the most telling parameter for the impact of particulates. When we collect a sample of particulates, we typically report the weight (much easier to measure). The weight fraction will be skewed towards the larger particle sizes. Never the less, actual, hard data is scarce on very low levels of particulates, either indoors or outdoors. People have been living with dust in their houses for centuries. There will always be some dust in the atmosphere from natural causes.

Thank you sharing your thoughts Carl.