In addition to climate change, air pollution is one of the biggest threats to human health. Small particles, known as particulate matter or PM2.5 (named for their diameter of only 2.5 micrometers or less), are a particularly dangerous type of pollutant. These particles are produced from a variety of sources, including forest fires and the burning of fossil fuels, and can enter our bloodstream, travel deep into the lungs, and cause damage to the respiratory and cardiovascular systems. Exposure to particulate matter causes millions of premature deaths worldwide every year.
In response to growing evidence of the harmful effects of PM2.5, the World Health Organization (WHO) has recently updated its air quality guidelinesReducing the recommended annual PM2.5 exposure guideline from 10 micrograms per cubic meter (μm) by 50 percent.3) up to 5 μm3. These updated guidelines represent an aggressive attempt to promote the regulation and reduction of anthropogenic emissions to improve global air quality.
A new study by researchers at MIT’s Department of Civil and Environmental Engineering is examining whether the 5 μm air quality guideline has been updated.3 is realistically achievable in different regions of the world, especially if anthropogenic pollutants are aggressively reduced.
The first question that the researchers wanted to explore was to what extent the transition to a future of non-fossil fuels would help different regions meet these new air quality guidelines.
“We have found that eliminating fossil fuel emissions would improve global air quality, but while this would help some regions comply with WHO guidelines, the significant contribution of natural resources in many other regions would hamper their achievement,” said Colette Heald, senior author, Civil and Environmental at MIT. Professor of Engineering and Department of Earth, Atmospheric and Planetary Sciences in Germeshausen.
A study by Heald, Professor Jesse Kroll, and graduates Sidhant Pai and Therese Carter, published June 6th magazine Letters in Environmental Science and Technology, finds that more than 90 percent of the world ‘s population is currently experiencing an average annual concentration that is higher than the recommended guideline. The authors further demonstrate that more than 50 percent of the world’s population would still be exposed to PM2.5 concentrations in excess of the new air quality guidelines, even in the absence of all anthropogenic emissions.
This is due to the large natural sources of particulate matter – dust, sea salt and plant organic matter – that still exist in the atmosphere when anthropogenic pollutants are removed from the air.
“If you live in parts of India or North Africa that are high in fine dust, it can be difficult to reduce exposure to PM2.5 below the new guideline,” says Sidhant Pai, one of the leading authors and graduate students. “This study forces us to rethink the value of different emission control measures in different regions and shows the need for a new generation of air quality metrics to enable us to make targeted decisions.
The researchers conducted a number of modeling exercises to investigate the implementation of the updated PM2.5 guidelines worldwide under different emission reduction scenarios.
Their models used a set of different anthropogenic sources that could be turned on and off to explore the contribution of a particular source. For example, the researchers conducted modeling that turned off all human emissions to determine the amount of PM2.5 pollution that can be attributed to natural and fire sources. By analyzing the chemical composition of PM2.5 aerosols in the atmosphere (e.g., dust, sulfate, and carbon black), researchers were also able to better understand the major sources of PM2.5 in a particular region. For example, increased PM2.5 concentrations in the Amazon have been shown to consist mainly of carbon-containing aerosols from sources such as deforestation fires. On the contrary, nitrogen-containing aerosols were popular in Northern Europe and were greatly contributed by the use of vehicles and fertilizers. Thus, these two regions will need very different policies and approaches to improve air quality.
“Analyzing particulate matter pollution for individual chemicals can lead to region-specific mitigation and adaptation solutions, rather than a one-size-fits-all approach that can be difficult to implement without understanding the importance of different sources. “,” Says Pai.
When the WHO air quality guidelines were last updated in 2005, they had a significant impact on environmental policy. Scientists could look at an area that did not meet the requirements and propose high-level solutions to improve air quality in the region. However, with the tightening of the guidelines, global solutions for managing and improving air quality are no longer so obvious.
“Another advantage is that some particles have different toxicity properties that are related to health outcomes,” says Therese Carter, one of the leading authors and graduate students. “This is an important area of research that this work can help motivate. Being able to separate that part of the puzzle can give epidemiologists more insight into the different levels of toxicity and the effects of specific particles on human health.
The authors believe that these new findings are an opportunity to extend and replicate the current guidelines.
“Conventional and global measurements of the chemical composition of PM2.5 would provide policy makers with information on which interventions would most effectively improve air quality in any given location,” said Jesse Kroll, a professor in the Department of Civil and Environmental Engineering and Chemical Engineering at MIT. . “But it would also give us new insights into how the various chemicals PM2.5 affect human health.”
“I hope that by learning more about the health effects of these different particles, our work and that of the wider atmospheric chemistry community can help develop strategies to reduce the most harmful pollutants to human health,” Heald added.
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