São Paulo, Brazil, is the world’s fifth-largest metro area, with 21 million people. It also struggles with extremely high — and often deadly — air pollution, most of it caused by the city’s 7 million road vehicles (and counting).
Yet a new paper in Atmospheric Environment points to another surprisingly significant source of urban pollution: delicious wood-fired pizza.
"People of all ages line up for hours outside pizzerias every Sunday evening and the city is home to around 8,000 pizza parlors that produce close to a million pizzas a day," a press release notes. It’s the pizzerias with wood-fired ovens that pose a problem. Collectively they burn some 307,000 tons of wood each year, a significant source of harmful particulate pollution in the city. When combined with unregulated air pollution from steakhouse barbecues and other restaurants, it all starts to add up.
To put that in perspective, lead author Prashant Kumar of the University of Surrey notes that steakhouse barbecue and wood-fired pizza oven emissions in São Paulo may be enough to negate much of the positive effect on air quality that has come from the city’s switch to biofuels. The city is unique in running its vehicle fleet largely on a mix of sugarcane ethanol and soy diesel, which has helped curb some pollutants (like sulfur dioxide) but possibly increased others (like ground-level ozone).
The bulk of the Atmospheric Environment paper discusses rather mundane (but important!) recommendations for tweaking São Paulo’s transportation policy to reduce vehicle travel and air pollution. (For instance, the authors point out that the city has just 78 kilometers of metro rail compared with London’s 402 kilometers.) Since vehicles are the key source of smog, that focus makes sense.
But it’s the pizzeria bit that grabs the eye. Pizza-makers prize wood-fired ovens because they can get super hot (up to 1,200 degrees Fahrenheit), allowing for an extra crispy and beautifully blistered crust. But wood-fired pizza ovens have also come under environmental scrutiny in recent years: In 2015, a small town in Italy banned traditional pizza ovens in restaurants over air-pollution concerns. Because the pizzeria chimneys are so close to ground level, their emissions can have a much bigger effect on local health than the pollution belching out of taller smokestacks in factories and power plants.
Fortunately, there are technologies that can clean up all that restaurant pollution — like filters or catalytic exhaust purifying systems. These technologies tend to get less emphasis than big public transportation reforms, but when you’re a megacity choking on smog, every little bit helps.
- Note that the deadliest environmental issue in the world remains indoor air pollution, killing 4 million people a year. To be clear, most of this is from indoor home stoves — pizzerias are a very small, uh, slice of the problem.
- By the way, the paper didn’t try to estimate the environmental impact of coal-fired pizza (there’s not enough data on these establishments), but Grist’s "Ask Umbra" column tried to take a crack at the question in 2010. It’s probably the most carbon-intensive way to make pizza, but it’s also negligible compared to the coal we use in power plants.