When residents began noticing a fine grit settling on their cars, lanai furniture and outdoor surfaces, the prevailing suspicion on Longboat Key pointed skyward — to the jets climbing out of Sarasota-Bradenton International Airport. After a $26,000 third-party investigation, the Town’s consultant told commissioners on June 22 that the evidence simply doesn’t support that theory.
“There was some concern about particulate matter that was showing up on vehicles and on furniture outside, and we needed to find out where it was coming from,” Town Manager Howard Tipton told the commission as he introduced the item at the afternoon Regular Workshop. “The initial concern was aircraft emissions.”
—Why the Town ordered the study
—The complaints had a plausible trigger. Residents connected the fallout to a change in aircraft flight patterns at the airport in 2024, and the Town wanted an independent answer rather than a hunch.
“There were resident concerns of particulate matter accumulating on surfaces throughout the community, and this was correlated to an aircraft pattern change that happened in 2024 at the Sarasota-Bradenton airport,” said Mark St. Marie, national technical lead for healthcare at The Vertex Companies, the environmental consulting firm the Town retained. “The Town asked us to provide a third-party, data-driven study.”
—St. Marie brought an unusually specific résumé to the question. “I’m also retired Air Force, a certified industrial hygienist, 36 years of practice,” he said. “I traveled around the world and the country doing aircraft emission studies for 22 years in the Air Force.”
—Looking for a “fingerprint”
—The central idea of the study, St. Marie explained, was that aircraft exhaust leaves a distinctive chemical and physical signature that can be separated from every other source in a community.
“What we’re looking for is a fingerprint that we can associate specifically with the aircraft that’s excluded from every other source,” he said.
—The timing of the sampling was deliberate. Vertex was hired in early March but waited until April to begin collecting data — in order to capture Longboat Key’s worst-case wind conditions.
“We really wanted to select the prevailing winds that are the worst case for Longboat Key,” St. Marie said. “The winds change from northern to southern-westerly, and that certainly carries it directly from the airport over to Longboat Key.”
—Over six days and 11 separate monitoring deployments, Vertex collected roughly 16,000 data points, combining real-time, direct-reading air monitors with laboratory analysis of collected samples. The firm measured particles of several sizes, screened for metals, volatile organic compounds and combustion byproducts, and tracked wind direction and noise to time particle “fallout” to the moments aircraft passed overhead. Monitors were set on tripods at ground level, six to eight feet up, at three Longboat Key locations — including the Positano community and the area near the Town’s public library. For comparison, Vertex also took “background” samples off-island near Interstate 75 and at a park near the Key’s north end.
—What the data showed
—On point after point, the aircraft signature failed to appear.
The particles Vertex found were predominantly the larger PM10 size, not the ultra-fine particles that jet thrust typically produces. “There was no repeatable fingerprint that we could associate specifically with the particle sizes,” St. Marie said.
The chemistry told the same story. “What we typically see with aircraft emissions is some very specific metals — things like chromium and cadmium that are only found in aircraft,” he said. “In this case, we didn’t find any metals in any of the samples.” He called that result unusual for this kind of study: “Typically, we do see metals.”
—The carbon profile pointed in a familiar direction. “The one thing we did find in the carbon footprint is a heavily weighted concentration related to gasoline and diesel engines,” St. Marie said.
—Critically, the Longboat samples looked just like the off-island comparison samples taken beside the interstate — similar in chemical makeup, particle size and concentration.
—The verdict: local sources, not the runway
“The study did not identify conclusive evidence of unique aircraft-related particle impacts,” St. Marie told the commission. “What we did find is that there are particles falling, but it’s not associated with the aircraft.”
—Pressed on the likely culprit, he didn’t hedge. “The likely contributor, in our professional opinion, is roadway traffic and marine activity, or local and regional combustion activities” — vehicle exhaust along Gulf of Mexico Drive, boats, and equipment such as golf-course and lawn machinery. Larger particles, he noted, “stay local. They don’t travel as far.”
—His recommendation was equally direct: stop spending on testing. “There’s really no immediate action that we need to take,” he said. “I wouldn’t recommend spending more money on any types of surveys. Having a communication with the airport is probably your best action to take.” He added that he “wouldn’t feel comfortable justifying more sampling in this case, even for Vertex.”
“Good news, bad news”
—Commissioners welcomed the finding but pointed out it doesn’t make the grit disappear.
“This is sort of good news, bad news,” Mayor Debra Williams said. “It’s good news that, with some confidence, it’s not coming from aircraft — but we still have it. It’s still something that we’re dealing with.” She pressed the point: “If I’m reading your report correctly, you’re saying this is just what we should expect — most likely from traffic along GMD and lawnmowers and things like that?”
“It could be — and it could be episodic, during this time when the winds change,” St. Marie answered. “I do think it’s coming from local sources, but it’d be great to see if it’s only related to certain times of year.”
—Residents push back on the timing
—The first resident to the podium questioned whether late April was a fair test at all.
“I think it’s difficult to judge a study done right now when there’s very, very little traffic,” said Diedre Greer of 6750 Gulf of Mexico Drive, at the Key’s far north end in Whitney Beach. “If this was done in the height of season, I think we would see a very different result.” Told the sampling ran at the end of April, she noted the north end’s traffic is “almost nonexistent right now.” Williams conceded the point: “Fair point.”
—Commissioner Sarah Karon raised a scientific wrinkle of her own — the region’s ongoing drought. St. Marie agreed it could matter. Dry air keeps fine particles from clumping together and dropping out, he explained: “These particles could have been so dry that they did not coalesce and did not fall in this case.”
—Commissioner Gary Coffin asked whether the monitors could distinguish leaf-blower and lawnmower debris (largely too coarse for what Vertex targeted) and whether mold or mildew had been measured. “It was beyond the scope of this contract,” St. Marie said. “We did not sample for those.” Commissioner Steve Branham asked the budget question directly, and St. Marie confirmed the fee: “$26,000 for the six days of sampling, with all the equipment and three people involved.”
—What the Town will do next
—Rather than commission more testing, staff signaled it will keep the conversation with the airport going — with a new angle.
“Based on this information, one of the things we’re going back to is taking a look at the noise from some of the low-flying aircraft,” Tipton said. “We’ve got a meeting coming up with the new airport director, and we’re talking with him about asking the airlines — instead of going off at 100% throttle, can they go 90% or 80%? It may not be a pollution reduction, but it could be a noise reduction.”
—St. Marie noted the Town has leverage on flight paths if it chooses to use it. “The FAA has the ability to change these things,” he said. “Based on community-impact studies and conversations with the community, they can change the routes and the frequency of how often they fly” at a given runway. The Town, he said, may also wish to keep documenting residents’ observations going forward.
