The body responds faster than we typically measure.
As climate change intensifies the frequency of heat waves and toxic air, a team of researchers at the City University of New York has taken a quiet but consequential step: using the devices already in people's pockets and on their wrists to trace, in real time, how the invisible environment shapes the body and the mind. The pilot study, small in scale but large in implication, suggests that the relationship between pollution and human health is far more immediate and individualized than the blunt instruments of traditional epidemiology have ever been able to show. What is being measured, ultimately, is not just air quality or heart rate — it is the cost of simply moving through a world that is growing harder to breathe in.
- As heat and pollution worsen globally, science has lacked the tools to capture their harm as it unfolds moment to moment inside a living day — until now.
- Combining Fitbits, GPS location data, and mood surveys, CUNY researchers built individualized exposure profiles that moved with participants through shifting urban environments, revealing physiological and emotional shifts tied to specific pollutants.
- Nitrogen dioxide correlated with disrupted heart rate variability, sulfur dioxide with rising nervousness and hopelessness, and one counterintuitive finding — heat linked to lower sadness — underscored how complex and context-dependent these relationships truly are.
- The pilot was deliberately modest, but researchers are already scaling to a larger NIH-funded study tracking how prenatal and current exposures shape adolescent brain development and mental health.
- The urgency is sharpest for those with the least protection — children, pregnant individuals, people experiencing homelessness, and lower-income communities — whose bodies absorb the heaviest share of a burden they did not create.
Climate change is making heat waves and air pollution more frequent and more severe, yet measuring how these forces harm people — moment by moment, as they move through their days — has always been elusive. Researchers at the City University of New York set out to close that gap using tools most people already carry: a smartwatch, a smartphone, and a willingness to answer brief questions about how they feel.
The pilot study asked participants to wear Fitbit smartwatches for roughly a month while completing mood surveys several times daily. Smartphone location data was layered in to estimate each person's real-time exposure to heat, nitrogen dioxide, particulate matter, and sulfur dioxide based on where they actually spent their time — not where they happened to live. The result was what co-first author Melissa Blum called an "individualized exposure profile" that traveled with the person throughout the day.
The findings were striking in their specificity. Higher nitrogen dioxide exposure shifted heart rate variability, a marker of the body's ability to recover from stress. Sulfur dioxide correlated with increased nervousness and hopelessness. One counterintuitive result — that higher heat was linked to lower self-reported sadness, possibly because warmth draws people outdoors and into social contact — reminded the team that cause and correlation still need untangling at larger scale.
Senior author Yoko Nomura described the study as a watershed moment, noting it is the first known effort to combine wearables, ecological momentary assessment, and continuous GPS tracking to measure environmental exposures and their immediate health effects. The researchers were careful not to overstate a small pilot, but the speed with which patterns emerged — physiological shifts lining up with where participants had been and what they had breathed — was itself a revelation.
The burden of these exposures falls hardest on those least able to escape them: children, pregnant individuals, people experiencing homelessness, and those with lower incomes. With lessons from the pilot already incorporated, the team is now scaling to a larger NIH-funded study examining how prenatal and current environmental exposures shape brain development and mental health in adolescents — pointing toward a future where real-time exposure data might one day inform clinical care for the most vulnerable.
Climate change is making heat waves and air pollution more frequent and more severe. But measuring how these exposures actually harm people—moment by moment, as they move through their day—has always been difficult. Researchers at the City University of New York set out to solve that problem by combining three tools that most people already carry: a smartwatch, a smartphone, and the willingness to answer quick questions about how they're feeling.
The pilot study, published in JMIR Formative Research, asked participants to wear Fitbit smartwatches for about a month while completing brief mood surveys several times a day. Researchers then layered in smartphone location data to estimate what each person was exposed to—heat, nitrogen dioxide, particulate matter, sulfur dioxide—based on where they actually spent their time. It's a simple idea in concept, but it required coordinating three separate data streams and making sure they all lined up in real time.
What emerged from the data surprised even the researchers. On days when participants encountered higher levels of nitrogen dioxide, their heart rate variability shifted—a physiological marker of how well the body recovers from stress. Exposure to sulfur dioxide correlated with increased feelings of nervousness and hopelessness. The relationship between environment and body turned out to be more intricate than traditional monitoring methods, which rely on stationary air quality sensors or assumptions based on where someone lives, could ever reveal. One finding was counterintuitive: higher heat exposure was linked to lower self-reported sadness, possibly because warm weather drives people outdoors and into social settings, though the researchers acknowledged that larger studies would be needed to untangle cause from correlation.
Sameera Ramjan, a doctoral student in psychology at the CUNY Graduate Center, noted that the speed of the discovery was striking. "We were struck by how quickly the data revealed patterns—changes in heart rate variability, shifts in mood—that lined up with where participants had been and what they were exposed to," she said. The approach captures something that traditional epidemiology cannot: the lived experience of moving through multiple environments in a single day, each with its own hazards.
Melissa Blum, a medical student at the Icahn School of Medicine at Mount Sinai and co-first author, emphasized the shift this represents. Instead of relying on a person's home address or a single monitoring station to estimate exposure, the system builds what she called an "individualized exposure profile" that moves with the person throughout their day. That distinction matters enormously for understanding real health impacts.
The pilot was small, and the researchers were careful not to overstate their findings. But Yoko Nomura, the senior author and a distinguished professor of psychology at CUNY, called it a watershed moment: "To our knowledge, this is the first study to combine wearable devices, ecological momentary assessment, and continuous GPS tracking to measure environmental exposures and their immediate health impacts." The work demonstrates that consumer technology and environmental epidemiology can be integrated in ways that could eventually reshape preventive medicine.
The stakes are high. Extreme heat and air pollution are increasing globally, and their burden falls heaviest on those least able to escape it: children, pregnant people, those experiencing homelessness, and people with lower incomes. Children face particular risk because environmental exposures during critical developmental windows can leave lasting marks on the brain and behavior. The researchers have already refined their system based on lessons from the pilot and are now scaling up to a larger, NIH-funded study that will examine how prenatal and current environmental exposures shape brain development and mental health in adolescents. The work is still early, but it points toward a future where clinicians might use real-time exposure data to make better decisions about patient care, especially for people whose conditions are sensitive to heat or air quality.
Citas Notables
We were struck by how quickly the data revealed patterns—changes in heart rate variability, shifts in mood—that lined up with where participants had been and what they were exposed to.— Sameera Ramjan, doctoral student, CUNY Graduate Center Psychology program
By combining wearable sensors, GPS data, and real-time surveys, we're able to build individualized exposure profiles that move with people throughout their day. That's a real shift from relying on stationary monitors or home addresses.— Melissa Blum, medical student, Icahn School of Medicine at Mount Sinai
La Conversación del Hearth Otra perspectiva de la historia
Why does it matter that you're tracking people in real time rather than just using air quality data from a fixed monitor?
Because people don't stay in one place. You might live in a neighborhood with decent air quality, but spend eight hours a day in a traffic-heavy area with high nitrogen dioxide. A stationary monitor would miss that entirely. Real-time tracking captures your actual exposure.
What surprised you most in the data?
How quickly patterns emerged. We expected to see correlations between pollution and stress markers, but the speed was striking—changes in heart rate variability that lined up almost immediately with where someone had been. It suggested the body responds faster than we typically measure.
The finding about heat and sadness was counterintuitive. What does that tell you?
It tells us the relationship between environment and emotion is more complicated than a simple cause-and-effect. Heat might reduce sadness because it drives people outdoors and into social situations. Or there could be seasonal mood patterns we're not accounting for. That's why we need larger studies.
Who benefits most from this kind of monitoring?
Right now, it's a research tool. But eventually, it could help clinicians make better decisions for patients with asthma, heart conditions, or other illnesses sensitive to air quality or temperature. And it could help identify which populations are being hit hardest by pollution and heat.
What's the next step?
We're scaling up to a much larger study funded by the NIH, looking at how environmental exposures during pregnancy and childhood affect brain development and mental health in adolescents. The pilot proved the method works. Now we need to see what it reveals at scale.