“Most of what we know about air pollution is based on ground-level data, but that’s not where many of the emissions are happening,” says Hilpert, who built remote control vehicles as a child. “Without a drone it’s not safe or it can be difficult to take these kind of measurements.”
Bernat Adria-Mora, a member of Hilpert’s team, is FAA-certified to pilot the drone, which could take off from property adjacent to a refinery, coal plant, or hydrofracking operation, and fill four or five sampling bags at varying altitudes. Learning how pollutants disperse in the environment, says Hilpert, is an important step to protecting the public’s health.
Dangerous Drips and FumesHilpert, who grew up near the Black Forest region of Germany, got his start as a mathematician and physicist, studying the movement of electrons in semiconductors. He transitioned to civil engineering at the University of Karlsruhe, where his PhD thesis looked at the fluid mechanics of oil and gas pollutants as they spread underground and mix with groundwater. He also translated his expertise in the wave-like movement of electrons to study a remediation technique that employs wave-like acoustic vibrations to break apart contaminants. One version of this technique employs a truck bouncing on a large steel plate; another, heavy weights dropped from a crane.
After completing a post-doc and research assistant professorship at the University of North Carolina at Chapel Hill, he joined the faculty at Johns Hopkins where he zeroed in on a ubiquitous pollution source: gas stations. In a study published last year in the journal Current Environmental Health Reports, he estimated that nearly 400 gallons of gas are released by a typical gas station every month through drips and vapors, a portion of which escapes into the nearby environment.
“Concrete has pores in it. It’s not impermeable,” says Hilpert. “These spills penetrate concrete and get into groundwater. It happens all the time.” The health risks are substantial: Gasoline contains benzene, a known carcinogen that is so toxic that two or three gallons of gas would foul ten swimming pools worth of fresh water.
No-drip nozzles, so far mandated only in California, cut back on some of the leakage, but they do nothing for vapors released through venting pipes connected to underground storage tanks. In ongoing research with an industrial partner, Hilpert is looking to get a more accurate measure of these releases.
Of course leaks also happen even before fuel gets to the gas station. Of the contested Dakota Access Pipeline, Hilpert says, “Anytime a pipe connects to another pipe, there is risk for spillage. It’s almost certain that some fuel will get out.” To some extent microbes in the ground can neutralize spills by metabolizing the chemicals. However, some chemicals like MBTE—which replaced lead as a gasoline additive in 1979 before being later phased out—are hydrophilic, which means they are attracted to water and therefore more likely to disperse in the environment. (Hilpert also studies a related problem: how microbes themselves spread in the environment—such as antibiotic resistant pathogens in soil contaminated by poultry waste.)
Cleaning Up the South Bronx and BeyondCloser to home, Hilpert is the principal investigator of a project funded through Columbia Center for Environmental Health in Northern Manhattan to measure air pollution in one section of the South Bronx. Directly north of Randalls Island, Harlem River Yards will soon be a massive distribution hub for Fresh Direct, the grocery delivery service. When it opens, the facility could see a thousand trucks coming and going in a single day, perhaps more. An increase in diesel emissions would likely be bad news for the health of people living nearby. Already, one in five children in the area has asthma—among the highest rates in the country.
The multidisciplinary team—including Steve Chillrud from Lamont-Doherty, David Evans of the Columbia Children’s Center for Environmental Health, and Diana Hernandez, assistant professor of Sociomedical Sciences—is partnering with South Bronx Unite, a local advocacy group, to conduct a pilot study to work with the community as they advocate for access to green space and clean air.
In the larger scheme of things, the best way to lower pollution is to switch to clean energy sources. To this end, Hilpert and collaborators at Johns Hopkins hold a patent for an advanced geothermal system that mimics a heat exchanger in an internal combustion engine. “The United States is full of hotspots that could produce giant amounts of energy,” he says. “It’s just a question of tapping in.”