May 7, 2020

Gas stove cooking routinely generates unsafe levels of indoor air pollution

Gas stove cooking routinely generates unsafe levels of indoor air pollution

In 2001, a major study of human activity patterns found that people in the US spend roughly 90 percent of their time indoors. It is safe to say that, in the age of Covid-19, that number is even higher. (Here in the Roberts household, it feels like we’ve hit 105 percent.)

We also do most of our breathing inside. So it’s a little odd that we don’t think more about indoor air quality. Outdoor air is the subject of titanic legal and regulatory battles going back decades. The six criteria air pollutants covered by the Clean Air Act — ground-level ozone, particulate matter, carbon monoxide, lead, sulfur dioxide (SO2), and nitrogen dioxide (NO2) — have fallen an average of 74 percent since the Act was passed in 1970.


And it’s a good thing, because an inexorably growing pile of research suggests that those pollutants are even more harmful to humans, at lower exposures, than previously believed.

Yet here’s the doozy: The Environmental Protection Agency (EPA) warns that “studies of human exposure to air pollutants indicate that indoor levels of pollutants may be two to five times — and occasionally more than 100 times — higher than outdoor levels.”

Despite those risks, there are no federal standards or guidelines governing indoor pollution. A patchwork of state and local standards protects consumers, inadequately.

One major source of indoor air pollution, it turns out, is the familiar gas stove, which relies on the direct combustion of natural gas.

Four research and advocacy groups — the Rocky Mountain Institute, Mothers Out Front, Physicians for Social Responsibility, and the Sierra Club — have released a new literature review, assessing two decades worth of peer-reviewed studies. They find that “gas stoves may be exposing tens of millions of people to levels of air pollution in their homes that would be illegal outdoors under national air quality standards.”

We’ll take a quick look at the evidence in the review and then discuss why natural gas companies have fought so hard, for so long, to fend off regulation of gas stoves. Finally, we’ll conclude that electrifying buildings is the only rational direction for forward-looking policy on health and the climate. (I’m nothing if not predictable.)

What cooking with gas is putting in your air

One reason the debate over cooking pollution is so murky and easily confused is that cooking of any kind produces some pollutants that are harmful if not properly handled. Applying heat to food produces particles — tiny particles (PM10, or 10 micrometers in diameter), tinier particles (PM2.5, or 2.5 micrometers in diameter), and even tinier “ultrafine” particles (100 nanometers in diameter) — that can exacerbate respiratory problems.

All cooking should be done in a properly ventilated space, and if your nose warns you something is up, you should open a window. Common sense is your guide.

But cooking through direct combustion of fuel produces more pollutants than electric cooking. This is especially true when cooking with wood or charcoal, which is common in the developing world (one reason millions of Indian women suffer respiratory problems), but it’s even true with gas, the “clean” combustion fuel.

For one thing, even in the absence of any food, gas combustion produces PM2.5 (one of the deadliest air pollutants) — research suggests gas cooking produces about twice as much PM2.5 as electric. It also produces nitrous oxides (NOx), including nitrous oxide (NO) and nitrous dioxide (NO2), carbon monoxide (CO), and formaldehyde (CH2O or HCHO). All of these pollutants are health risks if not properly managed.

CO is an invisible, odorless gas that, at high enough concentrations, causes dizziness, headaches, fatigue, disorientation, and eventually death. (In the US, 27 states require CO monitors by law.) Though research has found that the presence of gas stoves in the home is one source of elevated risk of CO poisoning, that generally only happens when something goes wrong: a gas stove with a pilot light, a poorly ventilated space, a burner left on, something like that. Among average people, symptoms start at around 70 parts per million (ppm).

Gas stove cooking routinely generates unsafe levels of indoor air pollution

A carbon monoxide detector, which many households do not have.

However, research shows that low-level CO exposure can exacerbate cardiovascular illness among people with coronary heart disease and other vulnerable populations. California’s ambient air quality standards cap CO exposure at 20ppm over a one-hour period or 9ppm over an eight-hour period.

“In homes without gas stoves, average CO levels are between 0.5 and 5 ppm,” the report says. “Homes with gas stoves that are properly adjusted are often between 5 and 15 ppm, whereas levels near poorly adjusted stoves can be twice as high: 30 ppm or higher.” Poorly adjusted stoves — incompletely burning fuel, inadequately ventilated — may yield ongoing, low-level CO exposure, putting the vulnerable at greater risk.

And then there’s NO2, also invisible and odorless, and one of the most familiar and well-studied pollutants. EPA research shows that exposure to NO2 — even small increases in short-term exposure — exacerbates respiratory problems, particularly asthma, and particularly in children.

There is no EPA standard for indoor NO2, but the standard for long-term outdoor exposure is 53 parts per billion (ppb.) However, effects have been documented at much lower exposures. A 2013 study of indoor NO2 from stoves found that, among children with asthma, “every 5 ppb increase in NO2 exposure above a threshold of 6 ppb” led to a measurable increase in wheezing and asthma severity.

A 2013 meta-analysis found that children’s risk of wheeze rose 15 percent for every 15ppb rise in NO2. In this 2006 study, “a 15ppb increment in NO2 exposure was found to be associated with a significant 50% increased annual risk of lower respiratory symptoms.” More recent EPA research also linked long-term NO2 exposure to “cardiovascular effects, diabetes, poorer birth outcomes, premature mortality, and cancer.”

Finally, research has linked ongoing NO2 exposure to reduced cognitive performance, especially in children. This 2009 study concluded that “early-life exposure to air pollution from indoor gas appliances may be negatively associated with neuropsychological development through the first 4 years of life, particularly among genetically susceptible children.”

The EPA has known about the dangers for a long time. A 1986 report from its Clean Air Advisory Committee to the Consumer Products Safety Commission (CPSC) urged the CPSC to do a better job of assessing the dangers — particularly related to NO2 — of indoor air pollution sources like gas stoves. Thirty-four years later, the natural gas industry is still fending off federal regulation of gas stoves.

In short, research shows that even low levels of NO2 exposure are dangerous, especially to the vulnerable. Yet the EPA’s own science shows that homes with gas stoves have around 50 percent, ranging up to over 400 percent, higher levels of NO2 than homes with electric stoves. Concentrations can often exceed US outdoor pollution standards.

Gas stove cooking routinely generates unsafe levels of indoor air pollution


When David Lu, CEO and co-founder of Clarity, an outdoor air pollution monitoring company, heard about the indoor air pollution research going on at RMI, Lawrence Berkeley Laboratory, and elsewhere, he got to thinking. “Out of curiosity,” he says, “I set up some [pollution monitors ] in my own home. The data was crazy.”

“During the hour I was cooking and baking” with a gas stove, he says, NO2 concentrations spiked “close to 200ppb.” Though concentrations died down afterward, they averaged 140 to 150ppb over the course of the hour, well in excess of the US outdoor NO2 standard of 100ppb for one-hour exposure. (In response to the latest science, Health Canada has lowered that country’s one-hour outdoor standard to 60ppb. Its indoor one-hour NO2 standard is 90ppb; the World Health Organization recommends 106ppb; the EPA, again, has no indoor pollution standards.)

Lu says concentrations were lower when he took steps to increase ventilation. “I’m definitely trying to open the window now, and the doors if possible, when I’m cooking,” he says, but as he acknowledges, not every user of every gas stove can do that every time they cook.

Vulnerable populations are most at risk from gas stove pollution

Children are at particular risk of health problems if exposed to indoor air pollution, and lower-income households are at higher risk of exposure.

As the EPA says, gas emits a whole stew of toxic chemicals, including the aforementioned PM2.5, NO2, CO, formaldehyde, and more. Research has found that all of those chemicals individually have negative impacts on health. Exactly how they combine to affect children’s respiratory systems is complex and not yet fully understood. It can be difficult to isolate individual factors.

However, the report says, “a meta-analysis looking at the association between gas stoves and childhood asthma found children in homes with gas stoves have a 42 percent increased risk of experiencing asthma symptoms (current asthma), a 24 percent increased risk of ever being diagnosed with asthma by a doctor (lifetime asthma), and an overall 32 percent increased risk of both current and lifetime asthma.”

Lower-income households are more likely to have more people living in smaller spaces, with less ventilation. That puts them at greater risk of unsafe NO2 exposure, as does the heartbreaking practice among low-income homeowners, uncovered in several studies, of using their gas stoves as a source of heat to supplement weak or broken furnaces.

Lower-income, African American, and Hispanic children already suffer asthma at higher rates than the national average, mainly because they are more likely to live near sources of outdoor air pollution (like roads and industrial facilities), which makes them more vulnerable to sources of indoor air pollution. Another 2018 study found that asthma costs the US $82 billion a year in “medical expenses, missed work and school days, and deaths,” all of which fall disproportionately on the most vulnerable.

Gas stove cooking routinely generates unsafe levels of indoor air pollution

A stove that has run out of propane, with an electric heater atop.
Gordon Chibroski/Portland Press Herald via Getty Images

Ventilation can help, but it isn’t enough

A properly installed and operated gas stove, with a properly installed and operated hood or fan that leads outside, seems to be no danger to those who live with it, except perhaps to those with the most compromised respiratory systems. But US consumers have little reason for confidence that their stoves meet those criteria.

Here’s a fun fact: Stoves are the only major indoor gas appliance not required to be vented outdoors. When it comes to gas furnaces, dryers, and water heaters, regulators have acknowledged the danger of indoor pollution and required a vent leading from the appliance outside.

A stove burns about as much gas as a dryer, but alone among major gas appliances, it faces no such requirement. There are no federal venting requirements for gas stoves in new buildings and, in many states, no state requirements either. Even in states or cities that require outdoor venting, there are few measures in place to ensure they are installed and operating correctly, or maintaining safe air quality.

The report offers four reasons to doubt whether ventilation is keeping people safe. First, many homeowners with gas stoves don’t have exhaust hoods or fans. Second, many existing hoods and fans simply recirculate the air (and pollutants) rather than venting it outside. Third, the performance of hoods varies widely, capturing anywhere between 15 and 98 percent of emissions, depending on positioning and air flow. Fourth, the people who do have them often don’t use them — they find them noisy or distracting, or just forget.

Whatever the theoretical potential of hoods and other ventilation to keep the air clean, it’s clear that current practices leave millions exposed to unsafe indoor air pollution. To remedy that, standards on ventilation and hoods would have to be tightened, made uniform, and enforced much more strictly.

Or the US could just decide to electrify its buildings, switching out gas stoves for electric stoves and induction cooktops. It’s the same choice as with power plants and cars: take the difficult, expensive, and perpetually inadequate steps necessary to better control the emission of toxic pollutants from fossil fuel combustion … or abandon fossil fuel combustion in favor of renewably generated electricity.

And in all three areas — power generation, transportation, and buildings — the choice grows clearer every day: renewable electricity reduces air pollutants, greenhouse gases, and, over the long term, consumer costs.

There are plenty of legitimate questions about how fast natural gas can be phased out of the building sector, and how much of that natural gas might be replaced with low-carbon biomethane or synthetic gas along the way, but the long-term direction is clear. (See here for more on the case for electrifying buildings.)

The natural gas industry does not, to put it mildly, agree.

The natural gas industry is using gas stoves to push back against electrification

Gas stoves play a special role for the natural gas industry in its fight against electrification. Most of its actual lobbying and policy advocacy is focused on space and water heating, but stoves are central to its marketing. Though they are not particularly large sources of demand, gas stoves are popular and still, at least in the US, associated with high-end chefs and cooking. The gas industry is playing hard on those feelings.

To wit, I give you “Natural Gas. Genius.” It is “a consumer marketing campaign that speaks from the heart and mind of today’s homebuyer/remodeler,” says the American Public Gas Association (APGA). “It’s refreshing, sassy and right on target with this target audience.”

This sassy campaign, funded at about $300,000 a year, says nothing about indoor air pollution or the gas industry’s opposition to electrification. Rather, it involves an array of attractive people representing a wide range of market demographics — including a special class of social media “influencers” — cooking with gas in videos across social media platforms.

Gas stove cooking routinely generates unsafe levels of indoor air pollution

Which one are you? Dibs on Young City Solo.

This amazing APGA presentation on campaign planning discusses how, in its next phase, the campaign can leverage influencers into “Super Providers,” who “go the extra mile to make things comfy, fun, and rewarding for the close people in their lives” (excluding, presumably, any asthmatic children in their lives).

For its part, the American Gas Association (AGA) has the similarly sassy #CookingWithGas, which features some delightful looking recipes prepared in kitchens with visibly inadequate ventilation.

“They’re coming to take your gas stoves” is a central message of Californians for Balanced Energy Solutions, an astroturf group formed to push back against electrification in California.

There’s more than stoves to that case, of course. If you’d like a more high-toned defense of the natural gas industry’s position on electrification, you can check out this op-ed from the Heritage Foundation (which conspicuously does not mention NO2).

It’s all part of a large, broad, and well-funded campaign against electrification being waged by the industry. APGA has the Media and Public Outreach Committee, set up by the industry with the goal of “winning the communications war” over electrification. AGA has the Sustainable Growth Committee and the Building and Energy Codes Committee fighting against electrification. The AGA’s position is that it will “oppose ‘electrification’ efforts that would prohibit, negatively impact, or limit consumer choice for the direct use of natural gas.”

(Another fun fact: APGA and AGA fund this astroturfing with dues paid to the organization by municipalities and ratepayers, many of whom support rapid action on climate change.)

This industry campaign — which I wrote about at greater length in this post — comes in response to a rapidly spreading grassroots “all-electric movement” that has dozens of towns, cities, and counties passing new building codes or ordinances to encourage electrification or, as in Berkeley, California’s case, simply prohibiting gas hookups in new buildings.

The industry has bottomless pockets, but it is fighting history here. It is losing its footing in the power sector and in the building sector, which will only continue as electricity is increasingly seen as clean, modern energy and burning fuels as dirty and old-fashioned, with more and more localities and states passing policy to accelerate the transition.

In the meantime, insofar as the industry wants to make gas cooking the face of its self-preservation campaign, gas cooking has been polluting indoor air for decades, at the expense of children and other vulnerable populations, and tens of millions of people remain at risk. (A 2014 study by scholars at LBL found that gas stoves routinely expose 12 million people in California to indoor levels of NO2 that would be illegal outside — and 1.7 million to unsafe levels of CO.)

Everyone should ensure that the area where they cook is well-ventilated, especially in these cooped-up days of coronavirus lockdown, with children at home all day. But for the individual homeowner, as for society at large, managing harmful pollution eventually starts to seem a little silly when equally effective, affordable, and pollution-free alternatives are available. It’s time to start making new buildings all-electric and switching out all those existing gas appliances, including gas stoves, for electric alternatives.

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