A Ride in a Chemical-Sniffing Van Shows How Heat Amps Up Pollution

Two vans loaded with precision instruments trundled along the streets of New York and New Jersey in the heat earlier this week, sniffing for toxic chemicals in the air.

They detected spikes in methane, a potent greenhouse gas, most likely from leaks, or from natural-gas-burning buses. They found plumes of nitrous oxide, possibly from wastewater. And all along the ride, they logged elevated levels of ozone, the main ingredient of smog, as well as cancer-causing formaldehyde — both of which form readily in hot weather.

The bottom line: The streets are dotted with pollution hot spots. And the heat makes pollution worse.

“If you want a chemical reaction to go faster, you add heat,” said Peter DeCarlo, an atmospheric air pollution researcher at Johns Hopkins University who’s leading an effort to use the vans to measure emissions along Louisiana’s petrochemicals corridor. “On hotter days, it’s the same idea,” he said.

Air pollution surges when temperatures rise, adding to the harms wrought by global warming. It’s one reason cities and counties across the Eastern United States hit by a heat wave this week have been issuing air pollution alerts.

The past three days, New York City has warned that ozone in the city is at levels “unhealthy for sensitive groups.” Detroit and Chicago have also issued air quality alerts this week. Drivers in Ohio, Michigan, Kentucky and Indiana have been urged to avoid refueling before 8 p.m., and to car pool or refrain from driving as much as possible, to cut down on fumes.

The bad air has to do with atmospheric chemistry, Prof. DeCarlo said, while his van navigated the South Bronx, East Harlem and Midtown with two New York Times journalists along for the ride. Pollution from burning fossil fuels reacts with heat and sunlight, forming ground-level ozone. Higher temperatures turbocharge that process.

Formaldehyde emissions, which can come from sources as diverse as wildfires and household products, also rise with higher temperatures. “The same chemistry that generates high levels of ozone also produces additional hazardous air pollutants, such as formaldehyde,” Prof. DeCarlo said.

Local hot spots can sometimes be seen. For instance, on some blocks in Manhattan, formaldehyde levels were double the surrounding areas, possibly from particularly dirty combustion caused by faulty equipment nearby.

The heat-pollution nexus is a growing concern worldwide. Health harms from extreme heat aren’t the only outcome of record-breaking temperatures. Air pollution also spikes when the temperatures rise, the World Meteorological Organization said in a report last year.

“Climate change and air quality cannot be treated separately,” Petteri Taalas, the weather organization’s secretary-general, said at the time. “They go hand in hand and must be tackled together to break this vicious cycle.”

Breathing elevated levels of formaldehyde and ozone has been linked to problems like respiratory irritation and inflammation, reduced lung function, and difficulties preventing and controlling asthma attacks. Exposure is particularly concerning in people with lung diseases like asthma or chronic bronchitis, said Keeve Nachman, an environmental-health and risk-assessment researcher at Johns Hopkins and a co-lead on the mobile monitoring effort.

By coincidence this week, as New York was getting struck by the heat wave, the research team had its pollution-sniffing vans in the city to demonstrate their technology.

Prof. Nachman said that while formaldehyde was carcinogenic to humans, cancers would be expected primarily from longer-term exposures, not from temporary increases.

It’s also important to recognize that chemical exposures don’t happen one at a time, and that we’re constantly exposed to groups of chemicals that may act together to harm our health, he said. “Hot days can create situations where people are breathing many harmful chemicals at the same time,” Prof. Nachman said. “Formaldehyde and ozone are perfect examples.”

One of the vans is set to return to Louisiana later this year to measure for as many as 45 pollutants from its petrochemicals industry, part of a project funded by Bloomberg Philanthropies’s Beyond Petrochemicals Campaign. In an initial peer-reviewed study published this month, the researchers found far higher emissions of ethylene oxide, a carcinogenic gas used in plastic production, than previously known.

Researchers piloting the van, a high-tech lab-on-wheels built by the environmental measurement tech company Aerodyne, can see pollution levels in real time, and even follow plumes to try to determine their source. “It’s a bit like a video game,” Prof. DeCarlo said. “And we’re able to measure everything all at once.”

Blacki Migliozzi contributed reporting.