Air pollution is a major threat to human health. Small particles known as PM 2.5 are a hazardous type of pollutant. These particles can enter our bloodstream, travel deep into our lungs, and cause respiratory and cardiovascular damage, from a variety of sources. Millions of premature deaths worldwide are caused by exposure to particulate matter.
The World Health Organization recently updated its air quality guidelines to take into account the increasing body of evidence on the harmful effects of PM 2.5. The updated guidelines are meant to promote the regulation and reduction of emissions in order to improve air quality.
The updated air quality guideline of 5 m 3 is being explored by researchers in the MIT Department of Civil and Environmental Engineering.
The researchers wanted to know if moving to a no-fossil-fuel future would help different regions meet air quality guidelines.
"Eliminating fossil-fuel emissions would improve air quality around the world, but it would be difficult for many regions to meet the WHO guidelines because of their high contributions from natural sources," says senior author Colette Heald.
More than 90 percent of the global population is exposed to average annual concentrations that are higher than the recommended guideline according to a study published in June. Over 50 percent of the world's population would still be exposed to PM 2.5 concentrations that exceed the new air quality guidelines even if there were no emissions.
Natural sources of particulate matter are still present in the atmosphere when emissions are removed.
Sidhant Pai, co-lead author and graduate student, says that it can be difficult to reduce PM 2.5 exposure in parts of India and northern Africa. The need for a new generation of air quality metrics that can enable targeted decision-making is suggested by the study.
In order to explore the viability of achieving the updated PM 2.5 guidelines worldwide under different emissions reduction scenarios, the researchers used a baseline year of 2019.
They used a suite of different sources to study the contribution of one source. The amount of PM 2.5 pollution that could be attributed to natural and fire sources was determined using a simulation that turned off all human-based emissions. The researchers were able to understand the most important PM 2.5 sources in a particular region by analyzing the chemical composition of the PM 2.5 aerosol. Concentrations of PM 2.5 in the Amazon were mostly comprised of carbon-based aerosols. Nitrogen-based aerosols were popular in Northern Europe. Both regions would need different policies and methods to improve their air quality.
"Analyzing particulate pollution across individual chemical species allows for mitigation and adaptation decisions that are specific to the region, as opposed to a one-size-fits-all approach, which can be challenging to execute without an understanding of the underlying importance of different sources."
The WHO air quality guidelines had an impact on the environment. Scientists could suggest high level solutions to improve the region's air quality if they looked at an area that wasn't in compliance. As the guidelines have tightened, globally-applicable solutions to manage and improve air quality are no longer visible.
Some of the particles have different toxicity properties that are related to health outcomes. This work can help motivate it. Being able to separate out that piece of the puzzle can give epidemiologists more insight into toxicity levels and the impact of particles on human health.
The authors see the new findings as an opportunity to make changes to the guidelines.
A professor in the MIT departments of Civil and Environmental Engineering and Chemical Engineering says that measuring the chemical composition of PM 2.5 would give policymakers information on what interventions would most effectively improve air quality. New insights into how different chemical species in PM 2.5 affect human health would be provided by it.
As we learn more about the health impacts of these different particles, our work and that of the broader atmospheric chemistry community can help inform strategies to reduce the pollutants that are most harmful to human health
More information: Sidhant J. Pai et al, Updated World Health Organization Air Quality Guidelines Highlight the Importance of Non-anthropogenic PM2.5, Environmental Science & Technology Letters (2022). DOI: 10.1021/acs.estlett.2c00203 Journal information: Environmental Science & Technology LettersMIT News ( web.mit.edu/newsoffice/) is a popular site that covers news about MIT.
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