Air quality in America's largest cities has steadily improved thanks to tighter regulations on key sources of particulate pollution. However, increased heat, wildfire smoke and other emerging global drivers of urban aerosol pollution are now combining to create a new set of challenges for public health officials tasked with protecting millions of people on the East Coast.
Research from Colorado State University published in npj Climate and Atmospheric Science begins to unpack and characterize these developing relationships against the backdrop of New York City. The research quantifies how existing particulate pollution from sources such as vehicle exhaust or consumer products are now combining with wildfire smoke –– transported from thousands of miles away –– to create secondary, often more toxic, pollution or contribute to the formation of ozone in hot weather.
Professor Delphine Farmer in the Department of Chemistry led the research with data collected from continuous on-the-ground readings at a site on Long Island during the summer of 2023.
"We did not set out to study air quality, wildfire and heat in that way, but smoke from fires in Canada arrived and, unfortunately, that is likely to be more and more common in the future," Farmer said. "Cities on the West Coast have been dealing with these combined issues for a while, but the developing situation in New York is a good test case to understand how variables like the nearby natural forests and denser populations on the East Coast may contribute to these emerging drivers of air pollution in mega cities."
Aerosol pollution consists of tiny particles of smoke or other compounds from many common sources such as cleaning solutions or cooking in restaurants. It can also occur naturally from the gases plants release every day. Hotter temperatures can cause plants to release more of those gases and speed the evaporation of some of those consumer products into particulate air pollution. Meanwhile, wildfire smoke particles absorb and react to those same gasses –– further amplifying both natural and man-made sources of pollution. Because these particles can enter the lungs, they may lead to heart disease, cancer and even dementia, making them a key focus area for health regulation.
Farmer said the situation in New York presented an opportunity to start to untangle the relationships between sources and their impacts overall. Her team found evidence that 90 percent of the aerosol pollution found over the city was indeed sensitive to at least one aspect of these global changes, such as high temperatures –– meaning effects from the pollutants were made worse during a heat wave, for example.
Some volatile chemical products such as paints and solvents are sensitive to these changes, and the team's work shows that those sources are responsible for more than double the estimated contribution from cars to the city's air pollution total in this category.
New York also has plenty of restaurants where the daily cooking and cleaning activities can contribute to overall pollution totals as well. However, the team found that while those emissions were also sensitive to the introduction of smoke or higher temperatures the effects were localized.
"We found that restaurants do have a big impact on their own local neighborhoods, but their associated aerosols are only a minor component of the total average load across the region," Farmer said. "Still, any worsening of those conditions from the arrival of wildfire smoke –– for example –– could lead to environmental health inequality for those areas that health policy makers will need to consider."
She added that context like that will help policy makers prioritize sources of pollution to target for both their overall contributions to the area's air quality and their localized impact on public health.
Machine learning techniques aid research into urban air pollution
Emily Franklin led aerosol data collection on the ground and follow-up analysis for the project as a CSU postdoctoral fellow funded by the National Science Foundation. She has since taken a position as a research scientist at CSIRO, Australia's national science agency.
Franklin said the team pulled measurements from many different instruments on the site and worked closely with fellow researchers from the universities of Minnesota, Columbia, Michigan and the University of California, Berkeley for the project. Together, these instruments generated thousands of individual indicators of aerosol composition, including characterization of hundreds of unique but unidentifiable compounds in the atmosphere. To take advantage of these complex measurements, she leveraged machine learning techniques.
"This was an incredibly rich and complex dataset. In a place like New York, you have compounds coming from trees in city parks, fires in Canada, construction sites miles away, and the barbecue joint up the road," Franklin said. "Machine learning was a powerful tool allowing us to embrace this complexity and leverage it to better understand how all of these sources interact with the climate to make the air pollution experienced by the community."
Funding for this project came from the National Oceanic and Atmospheric Administration as part of their AGES+ campaign, which is focused on improving air quality understanding through extensive, coast-to-coast observation using ground sites, research aircraft and satellite data.
The CSU team will now continue to study air quality in the region through the NSF funded GOTHAAM Campaign using a C-130 aircraft as a flying chemistry lab to measure atmospheric composition in real time across New York, New Jersey and Connecticut. That project focuses on volatile organic compounds –– a broad term for gases from car exhaust, industry, vegetation and consumer products that react in the atmosphere to form ground-level ozone, secondary organic aerosols and particulate matter.
Farmer said measurements taken from the plane will give the team a better sense of the chemistry happening in the region as they will be able to get readings over the ocean and at different altitudes. Ideally, they will be able to provide more information to the millions of residents in the broader region about their air quality and potential health risks from it.
"We worry about what we are breathing on the ground but in reality, the chemistry happening above us has a big impact on that. This research project will again help us understand key interactions better and improve our ability to predict potentially hazardous air quality conditions," she said.
