Scientists Launch GOTHAAM to Track Air Quality Above New York City

This past summer, scientists flew above New York City in an effort to study one of the most complex urban atmospheres in the world.

The Greater New York Oxidant Trace Gas Halogen and Aerosol Airborne Mission (GOTHAAM) is the largest airborne campaign ever conducted to measure precursors to smog in the area.

Funded by the National Science Foundation (NSF) and led by John Mak, a professor in Stony Brook's School of Marine and Atmospheric Sciences(SoMAS), the project brings together researchers from more than seven universities and the National Center for Atmospheric Research (NCAR).

For six weeks, the team - including SoMAS Professor Daniel Knopf, SoMAS Dean Paul Shepson and Christine Gilbert, an assistant professor in the School of Communication and Journalismand SoMAS - was based at MacArthur Airport on Long Island, conducting over 20 research flights using the NSF/NCAR C-130 aircraft, a large flying laboratory capable of carrying 13,000 pounds of instruments and flying low enough to capture detailed data across a range of environments.

"GOTHAAM is an intensive New York City-centric intensive field campaign that really focuses on the unique set of circumstances in this region," said Mak. "The population and industrial strength coupled with its location next to huge swaths of active forested areas, as well as being adjacent to the Atlantic Ocean, means you have three distinct areas all mixing together. In addition, we now have wildfire smoke to contend with regularly. This leads to a wide range of chemical processes that we don't fully understand. We want to understand those processes and the products, and how they impact our lives. The understanding we gain from this study will be directly translatable to other metropolitan areas around the world."

The New York metropolitan area (NYMA) regularly experiences air pollution events, especially during summer months. In 2021, seven of 11 monitoring stations in the region recorded ozone levels above federal health standards. While fine particulate pollution has declined, in large part due to decades of regulation, other factors such as gases released from vehicles, vegetation, industrial activity, and consumer products drive the formation of smog and secondary pollutants. These pollutants can worsen asthma and heart disease and also affect ecosystems in the metropolitan area.

To capture this complex chemistry, the C-130 aircraft is outfitted with a unique suite of state-of-the-art analytical instruments, including mass spectrometers, particle analyzers, and laser sensors that can detect hundreds of chemical compounds in real time. The flights, each lasting six to eight hours, crisscross the region from forests to city streets to the ocean. By sampling across these contrasting environments and tracking changes from day into night, GOTHAAM is expected to generate a high-resolution picture of atmospheric composition.

One of the central goals is to better understand volatile organic compounds (VOCs). VOCs are critical ingredients in the formation of ground-level ozone and particulate matter. In New York, VOCs come from a wide variety of sources: tailpipes, building emissions, industrial sites, consumer products like cleaning sprays and paints, and trees in surrounding forests. Forest emissions are especially important in the New York area, where wooded areas along highways and city outskirts may release more VOCs than intact forests. When these natural gases mix with urban pollutants, the chemistry becomes even more reactive.

The project also focuses on nighttime chemistry, a less studied but increasingly important area. During the day, sunlight drives most atmospheric reactions. At night, different scenarios emerge, involving nitrate radicals and chlorine compounds from sea salt. These reactions can form "reservoir" species that accumulate overnight and release pollutants when the sun rises, setting the stage for the next day's smog.

By flying during day and night hours, the GOTHAAM team aimed to capture these processes as they unfold.

"As you can imagine, it takes some time to figure out what all these data are telling us," said Mak. "Each instrument group - and there are about a dozen different groups - is tasked with getting their specific final data set ready for analysis, which takes a few months, and then we will be using different tools to figure out what is going on. The process will take many months."

The results from GOTHAAM will begin to emerge in the coming year, but researchers believe the data set will remain a baseline picture of pollutants and ozone for years to come. By examining the chemistry of one of the most densely populated regions in the world, the project aims to provide insights that can help protect public health both locally and globally.

- Beth Squire