I Bought a CO2 Monitor, and It Broke Me

A few weeks ago, a three-inch square of plastic and metal began, slowly and steadily, to upend my life.

The culprit was my new portable carbon-dioxide monitor, a device that had been sitting in my Amazon cart for months. I’d first eyed the product around the height of the coronavirus pandemic, figuring it could help me identify unventilated public spaces where exhaled breath was left to linger and the risk for virus transmission was high. But I didn’t shell out the $250 until January 2023, when a different set of worries, over the health risks of gas stoves and indoor air pollution, reached a boiling point. It was as good a time as any to get savvy to the air in my home.

I knew from the get-go that the small, stuffy apartment in which I work remotely was bound to be an air-quality disaster. But with the help of my shiny Aranet4, the brand most indoor-air experts seem to swear by, I was sure to fix the place up. When carbon-dioxide levels increased, I’d crack a window; when I cooked on my gas stove, I’d run the range fan. What could be easier? It would basically be like living outside, with better Wi-Fi. This year, spring cleaning would be a literal breeze!

The illusion was shattered minutes after I popped the batteries into my new device. At baseline, the levels in my apartment were already dancing around 1,200 parts per million (ppm)—a concentration that, as the device’s user manual informed me, was cutting my brain’s cognitive function by 15 percent. Aghast, I flung open a window, letting in a blast of frigid New England air. Two hours later, as I shivered in my 48-degree-Fahrenheit apartment in a coat, ski pants, and wool socks, typing numbly on my icy keyboard, the Aranet still hadn’t budged below 1,000 ppm, a common safety threshold for many experts. By the evening, I’d given up on trying to hypothermia my way to clean air. But as I tried to sleep in the suffocating trap of noxious gas that I had once called my home, next to the reeking sack of respiring flesh I had once called my spouse, the Aranet let loose an ominous beep: The ppm had climbed back up, this time to above 1,400. My cognitive capacity was now down 50 percent, per the user manual, on account of self-poisoning with stagnant air.

By the next morning, I was in despair. This was not the reality I had imagined when I decided to invite the Aranet4 into my home. I had envisioned the device and myself as a team with a shared goal: clean, clean air for all! But it was becoming clear that I didn’t have the power to make the device happy. And that was making me miserable.

CO2 monitors are not designed to dictate behavior; the information they dole out is not a perfect read on air quality, indoors or out. And although carbon dioxide can pose some health risks at high levels, it’s just one of many pollutants in the air, and by no means the worst. Others, such as nitrogen oxide, carbon monoxide, and ozone, can cause more direct harm. Some CO2-tracking devices, including the Aranet4, don’t account for particulate matter—which means that they can’t tell when air’s been cleaned up by, say, a HEPA filter. “It gives you an indicator; it’s not the whole story,” says Linsey Marr, an environmental engineer at Virginia Tech.

Still, because CO2 builds up alongside other pollutants, the levels are “a pretty good proxy for how fresh or stale your air is,” and how badly it needs to be turned over, says Paula Olsiewski, a biochemist and an indoor-air-quality expert at the Johns Hopkins Center for Health Security. The Aranet4 isn’t as accurate as, say, the $20,000 research-grade carbon-dioxide sensor in Marr’s lab, but it can get surprisingly close. When Jose-Luis Jimenez, an atmospheric chemist at the University of Colorado at Boulder, first picked one up three years ago, he was shocked that it could hold its own against the machines he used professionally. And in his personal life, “it allows you to find the terrible places and avoid them,” he told me, or to mask up when you can’t.

That rule of thumb starts to break down, though, when the terrible place turns out to be your home—or, at the very least, mine. To be fair, my apartment’s air quality has a lot working against it: two humans and two cats, all of us with an annoying penchant for breathing, crammed into 1,000 square feet; a gas stove with no outside-venting hood; a kitchen window that opens directly above a parking lot. Even so, I was flabbergasted by just how difficult it was to bring down the CO2 levels around me. Over several weeks, the best indoor reading I sustained, after keeping my window open for six hours, abstaining from cooking, and running my range fan nonstop, was in the 800s. I wondered, briefly, if my neighborhood just had terrible outdoor air quality—or if my device was broken. Within minutes of my bringing the meter outside, however, it displayed a chill 480.

The meter’s cruel readings began to haunt me. Each upward tick raised my anxiety; I started to dread what I’d learn each morning when I woke up. After watching the Aranet4 flash figures in the high 2,000s when I briefly ignited my gas stove, I miserably deleted 10 wok-stir-fry recipes I’d bookmarked the month before. At least once, I told my husband to cool it with the whole “needing oxygen” thing, lest I upgrade to a more climate-friendly Plant Spouse. (I’m pretty sure I was joking, but I lacked the cognitive capacity to tell.) In more lucid moments, I understood the deeper meaning of the monitor: It was a symbol of my helplessness. I’d known I couldn’t personally clean the air at my favorite restaurant, or the post office, or my local Trader Joe’s. Now I realized that the issues in my home weren’t much more fixable. The device offered evidence of a problem, but not the means to solve it.

Upon hearing my predicament, Sally Ng, an aerosol chemist at Georgia Tech, suggested that I share my concerns with building management. Marr recommended constructing a Corsi-Rosenthal box, a DIY contraption made up of a fan lashed to filters, to suck the schmutz out of my crummy air. But they and other experts acknowledged that the most sustainable, efficient solutions to my carbon conundrum were mostly out of reach. If you don’t own your home, or have the means to outfit it with more air-quality-friendly appliances, you can only do so much. “And I mean, yeah, that is a problem,” said Jimenez, who’s currently renovating his home to include a new energy-efficient ventilation device, a make-up-air system, and multiple heat pumps.

Many Americans face much greater challenges than mine. I am not among the millions living in a city with dangerous levels of particulate matter in the air, spewed out by industrial plants, gas-powered vehicles, and wildfires, for whom an open window could risk additional peril; I don’t have to be in a crowded office or a school with poor ventilation. Since the first year of the pandemic—and even before—experts have been calling for policy changes and infrastructural overhauls that would slash indoor air pollution for large sectors of the population at once. But as concern over COVID has faded, “people have moved on,” Marr told me. Individuals are left on their own in the largely futile fight against stale air.

Though a CO2 monitor won’t score anyone victories on its own, it can still be informative: “It’s nice to have an objective measure, because all of this is stuff you can’t really see with the naked eye,” says Abraar Karan, an infectious-disease physician at Stanford, who’s planning to use the Aranet4 in an upcoming study on viral transmission. But he told me that he doesn’t let himself get too worked up over the readings from his monitor at home. Even Olsiewski puts hers away when she’s cooking on the gas range in her Manhattan apartment. She already knows that the levels will spike; she already knows what she needs to do to mitigate the harms. “I use the tools I have and don’t make myself crazy,” she told me. (Admittedly, she has a lot of tools, especially in her second home in Texas—among them, an induction stove and an HVAC with ultra-high-quality filters and a continuously running fan. When we spoke on the phone, her Aranet4 read 570 ppm; mine, 1,200.)

I’m now aiming for my own middle ground. Earlier this week, I dreamed of trying and failing to open a stuck window, and woke up in a cold sweat. I spent that day working with my (real-life) kitchen window cracked, but I shut it when the apartment got too chilly. More important, I placed my Aranet4 in a drawer, and didn’t pull it out again until nightfall. When my spouse came home, he marveled that our apartment, once again, felt warm.



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