Particle-based ambient air pollution causes more than 4 million premature deaths every year worldwide, according to the World Health Organization. The smallest particles, 2.5 microns or smaller, known as PM2.5—pose the greatest health risk because they can penetrate deep into the lungs and even reach the bloodstream.
Although the total MP2.5 Levels have dropped 42 percent in the U.S. since 2000 as a result of clean air regulations, scientists are concerned about the health impacts of even low levels of such pollution. US Environmental Protection Agency lowered annual national air quality standard for PM2.5 12 to nine micrograms per cubic meter (μg/m3) this week. EPA Administrator Michael Regan said at a news conference that officials estimate the new rule will save up to $46 billion in avoided health care and hospitalization costs by 2032. “Health benefits will include up to 800,000 cases of asthma symptoms avoided, 4,500 premature deaths avoided, and 290,000 lost work days avoided,” he said. The World Health Organization adopted an even lower level of 5 µg/m3 standard in 2021, citing growing evidence of fatal damage.
Beyond investigating their size, scientists are also investigating the chemistry of airborne particles, which, unlike other regulated pollutants such as lead and ozone, encompass a wide range of solid and liquid particles, from soot to the nitrate. Some airborne particles are emitted directly from automobile exhaust pipes or industrial sources; others form in the atmosphere. And the balance between them is changing. To help states meet stricter air standards, scientists will need more detailed studies of particle sources.
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In July 2022, for the first time in more than a decade, teams of scientists conducted an intensive campaign to characterize what’s in the summer particle soup that New York City residents breathe. The researchers measured the chemical composition of the PM.2.5 over the course of a month.
The team discovered that the PM2.5 was 80 to 83 percent organic or carbon-based—compared to about 50 percent in 2001, according to the study, which was published Jan. 22 in ACS ES&T Air. “Over the past 20 years, summer particles have shifted to organic aerosols due in large part to successful reductions of sulfate and other inorganic compounds,” says Tori Hass-Mitchell, lead author of the study and doctoral student at the University from Yale.
About 76 percent of the total organic aerosols measured by the study in New York City were not emitted directly from a source, but instead formed in the atmosphere. These so-called secondary organic aerosols are produced when gases, including volatile organic compounds (VOCs), are oxidized in the atmosphere. VOCs are produced by a wide range of sources, such as automobiles, vegetation, and household chemicals, including cosmetics and cleanserswhich complicates efforts to identify the sources of greatest impact.
The paper by Hass-Mitchell and colleagues is the first to include data from the Atmospheric Chemistry and Science Measurement Network (ASCENT): A network of 12 sites in the US that is the first long-term monitoring system capable of chemically characterizing different types of particles. Sally Ng, who led the design of the $12 million network funded by the National Science Foundation, says Europe has had similar measurement capabilities for more than five years. “It’s time for the United States to modernize its air quality measurement infrastructure,” says Ng, an aerosol scientist at the Georgia Institute of Technology and co-author of the New York City study.
Recent studies have shown that secondary organic aerosols may be linked to serious health problems, especially cardiovascular disease. A study published last September in Environmental science and technology discovered that as organic aerosols oxidize, they produce highly reactive molecules that It can break down human cells and cause tissue damage.. Oxidized organic aerosols are the most toxic organic component of PM2.5says Ng. And his work suggests that secondary organic aerosols become more toxic the longer they are oxidized in the atmosphere.
EPA research scientist Havala Pye co-authored a separate paper 2021 Nature study which found that secondary organic aerosols are strongly associated with county-level heart and lung disease mortality rates in the US. Secondary organic aerosols were associated with a 6.5 times higher mortality rate than PM2.5.
“There’s a good chance that aerosols are becoming more toxic in terms of mass, and secondary organic aerosols would be part of the reason,” says Allen Robinson, an atmospheric scientist at Colorado State University, who was not involved in the new study. investigation. or Pye’s study. In other words, breathing more oxidized aerosols may be more toxic to humans. But the literature analyzing the health effects of individual components of PM2.5 It’s messy, Robinson notes. More work is needed to unravel the impact of complex combinations of different particle sizes and chemistries on PM.2.5, he explains. Pye also warns that consistent results from repeated experiments are needed to verify whether secondary organic aerosols carry significantly greater health risks than other particles that make up PM.2.5.
Will a warming climate worsen health risks from air pollution?
Previous studies have found that warmer temperatures can lead to increased production of these secondary organic aerosols. Hass-Mitchell and her colleagues found in the new study that secondary production of organic aerosols increased by 60 percent and 42 percent in Queens and Manhattan, respectively, during a sweltering five-day heat wave in July 2022. “We should expect greater health burdens as temperatures rise in a warming climate, with potentially more frequent extreme heat events in the future,” says Hass-Mitchell.
“Secondary organic aerosols are increasingly contributing to summer particulate matter and urban air quality, and (have) a temperature sensitivity that is really important to consider in the context of future climate scenarios,” says Drew Gentner, a Chemical and Environmental Engineer from Yale University and lead author of the new paper. These compounds “oxidize more at higher temperatures,” he adds, and rising temperatures can lead to greater emissions of reactive volatile organic compounds.
And as temperatures rise amid climate change, more frequent and severe wildfires have already begun to occur. reduce air quality improvements in the western states. Although Hass-Mitchell and her colleagues did not observe smoke from wildfires in the summer of 2022, they expect that organic aerosols from wildfires, such as those in the smoke that choked much of the northeast and midwest last summer—will also play an important role as the climate changes.
Many other cities, such as Los Angeles, Atlanta, and Seoul, have also documented a growing proportion of PMs.2.5 of secondary organic aerosols. But the exact mix of natural sources versus man-made sources varies widely from city to city. To continue reducing PM2.5“We need to understand the underlying sources and chemistry that contribute to the production of secondary organic aerosols,” says Gentner.
Until the early 2000s, both tools to measure secondary organic aerosols and understanding of their formation were limited, says Benjamin Nault, a co-author of the New York City study and a research scientist at Johns Hopkins University. Currently, most instruments are designed to measure aerosol size or chemistry, but not both, he says. Scientists rely on models to determine how much secondary organic aerosol comes from, for example, living vegetation, asphalt or the kitchen. But it’s not clear whether some sources are more harmful than others. “There are different signatures for chemicals that come from taking a shower or painting (a house),” he says. “Now we’re trying to understand how they come together in an urban environment.”
And that better understanding is leading to more nuanced pollution research. “As aerosol studies advance, with increasing capabilities to examine the various chemical components of aerosols, we can raise important questions about the relative impact of those components on air quality, human health and the environment” says Gentner. “Secondary sources of organic aerosols may be less straightforward to address compared to primary sources of pollution, but studies (like ours) show that secondary organic aerosols are the largest contributors in some urban areas.”
The report for this article was supported by the Nova Institute for Health.