Cooking Sunday roast causes indoor pollution ‘worse than Delhi’

Cooking a Sunday roast can drive indoor air pollution far above the levels found in the most polluted cities on Earth, scientists have said.

Researchers found that roasting meat and vegetables, and using a gas hob, released a surge of fine particles that could make household air dirtier than that in Delhi.

Fine soot and tiny organic particles from gas flames, vegetables, oils and fat combined to send harmful PM2.5 particulates in the house to levels 13 times higher than those measured in the air in central London. Peak indoor pollution lasted for about an hour.

“We were all surprised at the overall levels of particulate matter in the house,” said Marina Vance, who led the research at the University of Colorado in Boulder. She advised people to open windows and use extractor hoods if possible to ventilate the home while cooking.

PM2.5s are particles that are smaller than 2.5 micrometres across. They are small enough to be inhaled deep into the lungs where they exacerbate respiratory disorders and cardiovascular disease. Smaller particles can spread from the lungs into the bloodstream where they build up in the liver, heart and even the brain, where they may contribute to depression and other mental health issues.

In what Vance described as the most comprehensive investigation yet into chemicals in the home, the researchers cooked a series of meals in a three-bedroom test house fitted with indoor and outdoor pollution monitors. One day they cooked a Thanksgiving dinner with roast turkey, roast Brussels sprouts, boiled sweet potatoes, bread stuffing and cranberry sauce.

During the day of cooking, PM2.5 levels in the house rose to 200 micrograms per cubic metre for one hour, more than the 143 micrograms per cubic metre averaged in Delhi, the sixth most polluted city in the world, and far higher than the central London average of 15 micrograms per cubic metre.

Ranked on the US air quality index, a measure applied to city pollution, the indoor air was either “unhealthy” or “very unhealthy” for nearly two hours. The levels breached World Health Organization guidelines of 10 micrograms per cubic metre for eight-and-a-half-hours. The simple act of making toast sent PM2.5 levels up to 30 micrograms per cubic metre.

While gas flames and charred food churned out fine soot particles, others came from animal fat, cooking oils, and grime in the oven and and on pots and pans used in making the meal. Still more came from tiny particles of skin that the cooks and their guests shed from their clothes.

“We know that inhaling particles, regardless of what they’re made of, is detrimental to health. Is it equally bad as inhaling exhaust from vehicle emissions? That we don’t know that yet,” Vance said. “This compares to a very polluted city, but what’s important to remember is that this was for a short period of time. When you live in a polluted city you’re in it for 24 hours a day.”

Instruments around and inside the test home in Austin, Texas, found that when no one was cooking, the house kept outdoor air pollution out. But during a full day of cooking, the levels of particles indoors rose to about 30 times that outside.

Ian Colbeck, an expert in air pollution at the University of Essex who was not involved in the study, said he had measured particulates in his kitchen for the past 10 Christmases. “PM levels are much higher than in cities in the UK,” he said. “A roast is one of the worst ways of cooking as regards indoor air pollution.”

Vance was speaking at the American Association for the Advancement of Science meeting in Washington DC where researchers highlighted the risks of indoor air pollution from cooking, home furnishings, and household products such as bleach, window sprays and paint. Unlike outdoor pollution, which is regulated, indoor pollution is not, even though people spend as much as 90% of their time indoors, according to the US Environmental Protection Agency.

In one study, researchers looked for chemical contaminants in the blood and urine of children in 190 families. Some came from homes that had sofas containing flame retardants, and had six times the levels of the chemicals in their blood than other children. When children lived in homes with vinyl flooring, levels of hormone-disrupting phthalates in their urine were 15 times higher than those found in other children.

“As with any pollution there will be more susceptible groups such as the young and elderly,” said Joost de Gouw, another pollution researcher at the University of Colorado. “What’s clear is people spend a lot of time indoors and they are exposed in some cases to much higher levels than what you see outdoors.”

Vance advises people open windows and use kitchen extractors to remove the invisible pollution, but said it was unclear whether fans would help, since they recirculated air without adequately filtering it. “The joke we’ve been telling each other is boil everything, avoid roasting, but it’s too delicious,” she said.