Roadtrip Sleuthing Yields Surprising Data in Route to Houston

Purple vertical lines show chemical concentrations detected on a 3-day road trip from San Francisco to Houston. The higher the lines, the greater the concentrations. Map courtesy of Google Earth.

Heading south into Gilroy, California, on Friday morning right before Labor Day weekend, something seemed wrong: The mobile lab I was driving was measuring some of the highest levels of benzene my team and I had ever seen in the Bay area. We must have misconfigured something. Earlier that morning, I called my team in early to outfit the lab for emergency fieldwork. We had just decided late the night before to drive to Houston to monitor air quality after Hurricane Harvey. In the early morning hurry to load the analyzer into the van and pack for a week on the road, we were sure we had made a mistake.

As soon as we drove over the Pacheco pass, leaving the Bay area and entering the central valley, the benzene levels then dropped off, and we also noticed that a haze lifted. Then it hit us: the nearby forest fires that had been raging for days. Even though we could not see any fires from the road, their chemical signature was unmissable. There was no mistake. Our chemical sensor, AROMA, was doing just what it was designed to do, to see the invisible.

The Rim Fire in the Stanislaus National Forest in California.

On our 3-day road trip, this was to be the first major data point of many that showed us not only the power of our technology but also the diverse sources of benzene and other toxic aromatic chemicals in the environment. While we were focused on getting high-quality data to help Houston area residents, we also saw the tremendous opportunity that 3 days driving cross-country offered in understanding our instrument and what it can tell us about the environment. It was part chemistry and part data detective work.

Desert gas station

Our mobile lab was outfitted with the AROMA analyzer, connected into a laptop and an electrical system to keep it charged up a day at a time for continuous monitoring. The AROMA would draw in air samples every 12 minutes and then quickly analyze for toxic chemicals. From our laptop, we could configure the testing and see the data in real-time.

The AROMA works by spectroscopy and a fast chemical separation technique, targeting specific wavelengths of light absorbed by particular chemicals. We can select groups of chemicals with similar wavelength features, isolating those chemicals and ignoring others, allowing for rapid detection. Along with the chemical concentrations, the AROMA records the GPS coordinates, temperature, pressure, wind speed and other factors.

Among the aromatic chemicals, benzene’s toxicity profile is the worst, posing a high health risk as a known carcinogen. The sources of benzene are diverse, as it is a byproduct of incomplete combustion. So forest fires, ineffective catalytic converters on cars, cigarette smoking — all all emit benzene. It is also a component in petroleum. While federal law has limited benzene concentrations in gasoline to 0.62% since 2011, gas stations and leaking energy plants can still emit high levels of the chemical, as we saw firsthand.

Driving on Labor Day weekend, my colleague Mike Armen and I opted to cut across the Mojave Desert to avoid high traffic. We stopped at a little gas station in the middle of nowhere and saw what was to be the highest concentrations of benzene the whole road trip (at least until we got into Houston). The level was 22 parts per billion — that’s a factor of 10 lower than what we’d find near the leaking refineries in Houston but much higher than what refineries are allowed to emit.

The likely culprit? It’s hard to know for sure but we suspect faulty vapor recovery nozzles. These are the part of the nozzle on the gas pump that are supposed to prevent gases from emitting into the air. When you smell gasoline at a gas station, you are, in part, smelling benzene, which gives off a sweet smell. The nozzles are designed to reduce this odor and the associated pollution. But because this gas station was old, those nozzles may not have been working properly.

From a city center to a field of candles

The next highlight on our data detective road trip was crossing the border into Arizona and then approaching Phoenix. For reasons we don’t entirely understand, we started to see benzene concentrations increase as we crossed the border from California into Arizona. It could have something to do with different vehicle emission and safety standards or legacy regulations from before the federal government enacted stricter controls on benzene in gasoline. Historically, California has had very tough laws on vehicle emissions and gasoline, some of the toughest in the country.

In any case, we saw benzene concentration rise by a factor of 10 crossing the border and then rise by another factor of 10 as we entered the outskirts of Phoenix. The concentrations, around 1 part per billion, were higher than typical ambient conditions we see in California. We saw concentrations then rise again approaching El Paso, Texas, the next major city center.

AROMA was “seeing” the city centers before any buildings were in view. Urban areas have a different chemical profile than rural ones — a combination of more vehicles, more industry, more gas stations, and more people. Even though it intuitively makes sense, it was surprising and satisfying to see this in the data. And those insights just kept coming as the drive continued.

Gas flares like this lit up the Texas night sky along the drive.

Once in Texas, we were treated to the visually spectacular central Texas oil fields. Along a countryside road for miles, you see natural gas flares lighting up up the night sky. It’s like being surrounded by giant candles with tall flames billowing in the wind.

Ironically, as exciting as the light show was, it was one of the least active data points. Even though the oil fields are flaring out natural gas that contains benzene, the flares do not actually emit benzene. That’s because well-functioning flares burn off everything completely; benzene only emits from incomplete combustion.

Seeing is believing

To see an environment’s chemistry is real-time is truly awe-inspiring.

AROMA took readings all the way up to our arrival in Austin, where we met up with our partners at the Environmental Defense Fund to coordinate logistics for our effort in Houston. As before, the AROMA detected the city centers of both Austin and Houston upon approach.

The AROMA is happy taking measurements — it’s what it is designed for. So using it to collect a new dataset in route to Houston made perfect sense. It gave us an unparalleled opportunity to see what chemical concentrations looked like in different places, as well as more baseline for the fieldwork we would be doing in Houston.

To see an environment’s chemistry is real-time is truly awe-inspiring. We hope to collect more large datasets like this in the future, to inform further development of AROMA and to create a fuller picture of the environmental conditions across the country.

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Tony Miller is the CEO and a co-founder of Entanglement Technologies.


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