Is your favorite pizza joint hurting the environment?

A recent study found the wood-burning stoves used by pizzerias can damage the environment in major cities. 

Pizza poses a bigger environmental risk than you might think, according to a recent study published in the journal Atmospheric Environment.

While exploring causes of air pollution in São Paulo, Brazil, researchers found that restaurants using wood-burning stoves, such as pizzerias and steakhouses, are a significant contributor.

"It became evident from our work that despite there not being the same high level of pollutants from vehicles in the city as other megacities, there had not been much consideration of some of the unaccounted sources of emissions," said Prashant Kumar, professor in the Department of Civil and Environmental Engineering at the University of Surrey and lead author of the study, in a press release. "These include wood burning in thousands of pizza shops or domestic waste burning." 

Pizza shops are abundant in São Paulo: the self-proclaimed "Pizza Capital of the World" boasts approximately 8,000 pizzerias, which produce nearly a million pizzas a day between them. Pizza is a popular choice for dinner on Sundays, and an especially popular choice on July 10th, which is the city's annual "Pizza Day."

But this feasting comes at a cost. Each month, more than 7.5 hectares (about 18.5 acres) of eucalyptus forest are burned by pizzerias and steakhouses in São Paulo, Dr. Kumar said. In total, that's 307,000 metric tons (a little over 338 US tons) of wood per year sending up emissions.

"Once in the air, the emitted pollutants can undergo complex physical and chemical processes to form harmful secondary pollutants such as ozone and secondary aerosol," said co-author Yang Zhang, professor at North Carolina State University. Dr. Zhang was one of the 10 air pollution experts from seven universities who conducted the research, under the umbrella of the University Global Partnership Network. 

São Paulo has a compulsory green biofuel policy for all vehicles: Residents fill their cars with a biofuel comprised of sugarcane ethanol and gasoline (75 percent gasoline and 25 percent ethanol), and soybean biodiesel. But the pollutants created by the megacity's many pizza parlors is "significant enough of a threat to be of real concern to the environment, negating the positive effect" of the biofuel policy, Kumar said. 

All around the world, it seems that pizza, however potentially polluting, is here to stay. There are 74,812 pizzerias in the United States alone – and that's 3,425 more than there were in 2013. Of course, most do not use wood-burning ovens.

But given the popularity of pizza, how can we keep our air clean and eat our pizza, too?

One town in Italy attempted to answer that question last December, when it introduced a new ordinance to regulate pizzamakers and other restauranteurs using wood-fired ovens. 

San Vitaliano, a small town outside Naples, has banned the use of wood-fired stoves not equipped with filters that reduce air pollutants.

The announcement was met with outrage from pizzeria owners and residents, who held protests and argued that wood-burning stoves were not the "real cause" of the town's high pollution levels, the BBC reports. Mayor Antonio Falcone, who introduced the ordinance, became known as "the anti-pizza mayor."

The new law went into effect in March, so the long-term effects of the ban are unknown. Pizza ovens aren't the main cause of air pollution in San Vitaliano, Mr. Falcone told The New York Times, but he hopes the filters will at least draw attention to the greater environmental issues at hand. 

"We’re the first people who enjoy pizza, but the question is bigger," he said. "There’s an anthropological disaster in play. The important thing is to make people aware and sensitive."