In 2016, the Chilean national soccer team won a championship match against Argentina in nail-biting overtime. That same day, air pollution levels spiked in Chile’s capital city. Now scientists have figured out why: Santiagans had fired up roughly 100,000 charcoal barbecues while they watched the televised match, and combustion from the grilling triggered record-breaking levels of PM2.5 pollution. (PM2.5 describes atmospheric particulate matter smaller than 2.5 micrometers.) These results suggest that days of poor air quality can be predicted by considering large-scale cultural events.
In Santiago, levels of PM2.5, which can enter the lungs and inhibit respiration, occasionally spike to tenfold above average values for a few hours. Rémy Lapere, an atmospheric chemist at the École Polytechnique in Palaiseau, France, remembers modeling Santiago’s PM2.5 data from June 2016 when he stumbled upon two such spikes. “I had no idea they existed,” he said.
Not the Usual Suspects
Lapere’s curiosity was piqued, but he and his collaborators quickly ruled out the usual suspects that might have triggered the upticks. Wildfires probably weren’t the cause—no large ones had been reported. (It was winter, after all.) Furthermore, the pollution signal was strongly heterogeneous among Santiago’s 11 meteorological stations—a significant fire would have sent a plume over most of the city. Traffic was also exonerated—a tenfold increase in emissions would have implied a major road snarl, and none were reported during the times of the spikes. Residential heating, another big contributor to PM2.5 pollution, was likewise in the clear—it wasn’t any colder than normal on the days of the spikes, Lapere and his colleagues found.
The team next analyzed concentrations of PM2.5, nitrogen oxides (NOx), and carbon monoxide (CO) during the spikes and at other times. They found significantly lower NOx/CO and NOx/PM2.5 ratios during the spikes than during nonspike times. That’s highly suggestive of different emission sources, the team concluded.
“The chemical footprint didn’t add up,” said Lapere.
“It’s Soccer Games”
Lapere decided to reach out to a Chilean colleague for ideas. The scientist, who happened to be a sports fan, inquired about the dates of the spikes. He knew right away what it was, said Lapere. “It’s soccer games.”
Of course, the soccer matches themselves weren’t producing the emissions. They were simply the motivation for a Chilean cultural tradition that happens to create pollution. Chileans tend to celebrate events, including important soccer matches, by barbecuing, said Francisco Barraza, an environmental scientist at the University of Otago in New Zealand not involved in the research who earned his undergraduate and graduate degrees in Chile. Chunks of meat are cooked for multiple hours over charcoal, and all those open fires release particulate matter, said Barraza. “It’s like putting a running bus in your garden for 3 hours.”
The two spikes that Lapere and his collaborators found—18–19 and 26–27 June 2016—corresponded to televised matches of the Copa América, a South American soccer tournament, that involved the Chilean national team: Mexico versus Chile in the quarterfinals and Argentina versus Chile in the championship game, respectively. (Chile would go on to win, 4–2.)
To verify that barbecuing (asado in Chile) was the culprit, Lapere and his colleagues mined published NOx/CO and NOx/PM2.5 ratios associated with barbecuing. They found values consistent with their measurements during the spike events.
A Hundred Thousand Barbecues
A week prior to the championship Argentina versus Chile match, Santiagans were polled about their game day habits, and 29% reported they’d barbecue during the game. Assuming that barbecue gatherings involve roughly seven adults, that translates into about 100,000 barbecues, Lapere and his collaborators estimated. The researchers modeled the PM2.5 emissions from 100,000 barbecues and compared their simulations with the data from 26–27 June.
“The simulation reproduced the observations properly,” said Lapere. In other words, the meteorological data were consistent with the emissions from about 100,000 barbecues, the scientists concluded. These results were published last month in Atmospheric Chemistry and Physics.
Cultural events in other countries have also been shown to be associated with increases in pollution. For instance, Oktoberfest in Munich, Germany, is a significant source of methane, and researchers have measured upticks in PM2.5 levels after Lantern Festival celebrations in Beijing.
—Katherine Kornei (@KatherineKornei), Science Writer