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Scientists have investigated a poorly understood type of air pollutant. Lamarr Golding/EyeEm/Getty Images
  • Air pollution is responsible for the deaths of around 7 million people each year — and 91% of the global population is exposed to air that exceeds the limits on pollution levels set by the World Health Organization (WHO).
  • Fine particulate matter is a key source of air pollution. This can be directly produced or indirectly produced when other pollutants react to chemicals in the atmosphere.
  • In a new study, researchers highlight another type of pollutant, called anthropogenic secondary organic aerosols (ASOAs), which also react with other pollutants.
  • The researchers show that ASOAs are likely to significantly contribute to mortality associated with air pollution.

In a new study, a team of scientists has shown that an under-researched type of pollution, ASOAs, make a significant contribution to air pollution mortality.

For the researchers, their findings, published in the journal Atmospheric Chemistry and Physics, highlight the need for greater focus on these types of aerosols and the need for further research into how, when, and where they react with other pollutants to cause air pollution.

According to the WHO, about 7 million people die each year due to air pollution. The organization also reports that over 90% of the world’s population breathes air that exceeds the WHO’s safety standards for air pollution.

Researchers have found that fine particulate matter is a leading cause of this pollution — and that deaths due to fine particulate matter have increased from 3.5 million per year in 1990 to 4.2 million per year in 2015.

According to the Environmental Protection Agency, fine particulate matter can be caused directly or indirectly. Some direct sources of fine particulate matter include fires and construction sites.

Indirect sources include chemicals such as nitrogen oxides and sulfur dioxide, which can be emitted from the burning of fossil fuels and react with other chemicals in the atmosphere to produce fine particulate matter.

One type of chemical that can contribute to the formation of fine particulate matter are ASOAs. Previously, research has shown that these chemicals — found in inks, cleaning products, adhesives, and paints, for example — are a major source of volatile organic compounds that contribute to fine particulate matter.

Speaking to Medical News Today, Dr. Benjamin A. Nault, from the Center for Aerosol and Cloud Chemistry, at Aerodyne Research Inc., in Billerica, MA, and a lead author of the research, defined ASOAs as “particulate matter that is formed through [the] chemistry of organic compounds emitted from human activities.”

“These human activities include driving vehicles (emissions from tailpipes), cooking (charcoal emissions), heating (charcoal or wood), and volatile chemical products […] such as paint, adhesives, inks, cleaners, asphalt, etc. Some examples of these organic compounds include benzene, toluene, and xylenes.”

In their study, the researchers wanted to further confirm the role that ASOAs play in fine particulate matter pollution.

Dr. Nault told MNT that determining the amount of ASOAs is crucial to this.

“Particulate matter can be broadly classified as either primary or secondary. Primary particulate matter is particulate matter that is directly emitted from a source — think about the black smoke you may see coming out of a diesel vehicle or the smoke you see from a campfire or forest fire.”

“Secondary particulate matter is particulate matter that is produced by emissions that have undergone chemistry in the atmosphere — think about the sulfur dioxide that is emitted from coal fire plants that leads to acid rain,” Dr. Nault added.

“Due to this chemistry, secondary particulate matter can be more challenging to regulate, as you have to know both the emissions and the chemistry that leads to the particulate matter that is being observed and that can lead to health impacts. The secondary organic aerosol is one of the most difficult to regulate, as it is estimated that there are [thousands] of organic gases in the atmosphere from various emissions.”

“Once these emissions enter the atmosphere, they can undergo rapid chemistry, which (a) allows them to become particulate matter but (b) can make it more challenging to trace that compound to an emission source. This combination of emissions and chemistry has led to a large effort from the research community to be able to understand secondary organic aerosol production and how it may impact human health,” explained Dr. Nault.

“However, many studies have typically not [been] able to predict the amount of secondary organic aerosol that has been observed. Our research was able to predict the amount of secondary organic aerosol for various cities and different emissions around the world, providing confidence that we could start investigating how secondary organic aerosol impacts human health.”

According to Dr. Brian McDonald, of the National Oceanic and Atmospheric Administration Chemical Sciences Laboratory, in Boulder, CO, and a co-author of the study, “What’s new here is that we are showing this is an issue in cities on three continents, North America, Europe, and East Asia.”

According to Dr. Nault, “The older idea was that to reduce premature mortality, you should target coal-fired power plants or the transportation sector.”

“Yes, these are important, but [we are] showing that if [you are] not getting at the cleaning and painting products and other everyday chemicals, then [you are] not getting at a major source.”

To determine the significance of the contribution of ASOAs to fine particulate matter, Dr. Nault and colleagues drew on data from 11 studies that had analyzed air quality over the past 20 years.

The data came from cities across the world, including New York, London, and Beijing.

The researchers then used air quality models that also include satellite information to analyze the data. This allowed them to determine the contribution that ASOAs make to fine particulate matter, as well as mortality caused by fine particulate matter.

The researchers found a strong correlation between the production of ASOAs and volatile organic compounds, which react in the atmosphere to create fine particulate matter.

Using the models, the researchers estimate that ASOAs cause between 340,000 and 900,000 premature deaths each year. According to Dr. Nault, “[That is] more than [10] times as many deaths as previously estimated.”

While regulations on air pollution emission have increased over time, ASOAs have seen relatively little regulation.

Speaking to MNT, Prof. Jose-Luis Jimenez, of the Cooperative Institute for Research in Environmental Sciences, at the University of Colorado Boulder, and a corresponding author of the study, said, “The key problem is that the importance of ASOAs for mortality has not been recognized.”

“Previous studies concluded that the impact was small, and therefore, there was no urgency to regulate the chemicals that are most important to create ASOAs. Our research shows that the impact is quite large, and this recognition is the first step towards regulation. Then there is a need for research that provides more detail on the specific products and chemicals that are most important and to develop regulations to address these sources.”

“It is similar to the way ozone pollution has been regulated: First, it was recognized as a problem in Los Angeles in the 1950s and 1960s and started to be regulated. As more was learned about the chemistry that led to ozone pollution, the regulations were more targeted and effective. But ozone pollution is still a problem in many places (for example, in Colorado this summer), as these pollutants are difficult to reduce to low levels and need continuing efforts.”

Speaking to MNT, Dr. Nault said that to develop the findings of the present study, more research needs to be done globally, and that a more detailed understanding of the makeup of ASOAs and fine particulate matter is needed.

“This research is just a starting point for [a] better [understanding of] secondary organic aerosol in urban areas and how it directly impacts human health. A big first area that needs to be added to this research is more observations around the world, especially throughout Central and South America, throughout Africa, and throughout Central, South, and Southeast Asia.”

“We generally expect similar results [to what] we found in this research; however, this data would provide valuable insight into what the emissions are in these regions, whether trends we found in our research holds in these areas, and what the health impacts from [ASOAs] may be in these regions.”

“Further, a better understanding of what is actually being emitted from these volatile chemical products, products that are used in everyday usage, is needed to better understand how [they] impact indoor and outdoor air quality and how these volatile chemical products [may be] similar or different for different regions around the world.”

“Finally, we use total particulate matter to describe the health effects from this pollution; however, we would think that certain material in the particulate matter would be worse for health effects. Continued research in understanding what is actually in particulate matter, including [ASOAs], and what material leads to the health effects can lead to better emissions standards and improved health.”

Dr. Nault said that as an individual, using cleaner modes of transport, avoiding the use of solid fuels, and purchasing low emission products can make a difference to how much we contribute to air pollution.

“Transportation is still an important source of ASOAs and particulate matter. So, making sure that your vehicle is well tuned and taken care of ensures reduced emissions. If possible, using mass transportation or cycling will overall reduce this contribution further, as [having] fewer [individual] cars in urban areas will improve emissions.”

“Reducing solid fuel use (charcoal, wood), when possible, is another important step in reducing contribution to ASOAs. Some localities have been pushing for ‘low emissions’ products, such as low emission paint. If low emission products are available, and you have the choice and ability to get such products, that will also lead to overall lower contributions of ASOAs.”