During the Copa América Centenario of 2016, the intendente of the Región Metropolitana de Santiago, Claudio Orrego, made waves by stating that catastrophic levels of air pollution in Santiago were produced by barbecues (asados) associated with games of the Chilean National Soccer Team. Everybody laughed, because that’s ridiculous, here’s the government bullshitting around and trying to ban asados, etc. Meat was grilled, Chile won two consecutive Copa Américas, life went on. And yet, during these last several austral winters, game days were marked by the inescapable odor of wood smoke, that accentuated the already poor quality of winter air in Santiago. Could there be something to this theory after all? The Crampon Blog investigates.
Chile struggles with air pollution, a consequence principally of the unique topography of the country. Population centers in central Chile are located in the Central Valley, a depression bounded to the west by the Coastal Ranges and to the east by the Principal Cordillera of the Andes. In winter, it is not uncommon for a climatic inversion to form, wherein cold air in the valley bottom fails to escape the Central Valley. Atmospheric contaminants can then accumulate to create a soupy mixture of particulates, CO, NOX, and SOX. A similar phenomenon occurs in Salt Lake City, Utah, and Fairbanks, Alaska. In an effort to control particulate emissions there is a moratorium on burning firewood and charcoal (leña) for heating in Santiago. The exception, of course, is the burning of leña for asados.
The asado forms an integral part of Chilean celebratory culture. It consists of an open grill over which a variety of meats, mostly pork sausage and beef, are roasted. Due to the expense and labor involved, asados are normally reserved for special events when family and friends come together—they are typical of Chilean Independence Day and national celebrations. Another event that would qualify as “special” in the hearts of Chileans are games of the national soccer team. Of late the Selección Chilena has experienced a tremendous run of form, due to the foundations laid by manager Marcelo Bielsa in the early 2010’s and the “golden generation” of players centered around Alexis Sánchez, Arturo Vidal, and Claudio Bravo. Chile reached the group of 16 in the 2014 World Cup, narrowly losing to Brazil on penalties, and defeated Argentina twice on penalties to win both the 2015 Copa América and the 2016 Copa América Centenario.
Anecdotally, a phenomenon I observed in 2015 was that preemergencias medioambientales (“environmental pre-emergencies, when additional restrictions on vehicular traffic are imposed) were often declared on Sunday evenings, affecting Monday mornings. This is somewhat counterintuitive to the prevailing wisdom that vehicles and industry are the most potent contributors to air pollution in the Región Metropolitana, as on Sundays few drive and fewer work. It suggests that something weekend-specific contributes significantly to pollution in the zone.
Information on air quality, as well as limited meteorological data, are available from the Sistema de Información Nacional de Calidad del Aire, run by the Ministry of the Environment. Of the eleven stations in the Región Metropolitana, four were singled out by Intendente Orrego as stations that showed a high “Asado Signal,” meaning a spike in airborne contaminants coincident with matches of the Selección Chilena. These were Cerrillos / Cerrillos I, Cerro Navia, Pudahuel, and Quilicura / Quilicura I. They are located in the western part of the city, which is generally lower-income and lie at some of the lowest elevations in the Región (~500m amsl).
I have plotted an hourly time series of particulate matter less than 2.5 microns in diameter (PM2.5) over three periods of time: June 1-July 15 2014, June 1-July 15 2015, and June 1-July 1 2016. These periods of time correspond to the 2014 FIFA World Cup, 2015 Copa América, and the 2016 Copa América Centenario, respectively. In addition, I have marked the match start time of games featuring the Selección Chilena on each plot. The data, sorted by station, follow:
Certain extreme air pollution events correspond to kickoff times of soccer matches. Some events (e.g. Chile-Mexico 2016) show an order of magnitude increase in PM2.5 concentrations, measured in micrograms per cubic meter of air. The United States Environmental Protection Agency considers a maximum 24-hour exposure of 35 micrograms per cubic meter to be the “safe” standard for PM2.5; hourly concentrations of PM2.5 briefly exceeded 500 micrograms per cubic meter during this match.
Interestingly, only a few specific matches seem to possess a relationship with PM2.5 spikes. An additional determinant factor appears to be the day in the week in which a match falls. Matches that occur over the weekend (on the charts, labeled dates mark 12AM Saturday) are more likely to show a spike in PM2.5. Weeknight matches are generally not so pronounced in their relationship between PM2.5, if it exists at all. Some games that fall over weekend or holiday periods also do not show a relationship between PM2.5; we hypothesize that this is due to the relative importance of a game—less-significant games (latter matches in the group stage, or alternatively games against weak teams) might not necessarily elicit the same environmental effects as an important game.
Of note is the restricted geographic extent of the “asado signal.” Below are trends in PM2.5 over the same time period, but in Las Condes, an affluent part of the city that also lies at a significantly higher elevation:
Similarly, the asado signal is not generally perceptible in the outer regions, or at least is difficult to distinguish between the asado signal and background variability. Here is a chart from Temuco, where a strong diurnal periodicity of PM2.5 is produced by the heavy use of leña for residential heating, and where air quality approaches apocalyptic levels in the austral winter:
Each game does not correspond to peaks in PM2.5, nor does “match importance” explain 100% of the variability within the association. We think climate may serve as a conditioning factor that determines whether or not asados could impact PM2.5—only if climate conditions are “right” can asados have a significant effect on air quality.
Consider the concentration of PM2.5 (black) at Estación Cerro Navia in 2014, as compared to three climatic factors: temperature (T; red), relative humidity (RH; blue), and wind speed (green):
If I may draw your attention to temperature and relative humidity: the two factors covary diurnally, which is unsurprising, as relative humidity is a direct function of atmospheric temperature. However, both show some degree of weekly variability, in which periods of low diurnal variability in T and RH (~flat parts) vary with periods of high diurnal variability in T and RH (dogtooth parts)—for example, the periods from 10-13 June vs. 14-19 June, respectively. From 10-13 June, relative humidity was high and temperature was low; from 14-19 June, relative humidity fluctuated but was generally drier and daily temperatures were higher. High overall levels of PM2.5 correspond to these periods of high variability; that is, drier, warmer periods at the weekly scale. In addition, these periods—14-19 June for example—correspond to minima in surface wind velocity. When these criteria are not met, pregame asados might not provoke a response in PM2.5—see, for example, the quarterfinals of 4 and 5 July.
The basic climate analysis reveals some potentially interesting details about factors related to weekly pollution variability. Consider 2016 in Cerro Navia:
I would argue that a reliable indicator of general air pollution spikes during this time of the year (not necessarily related to asados) is the minimum 24-hour relative humidity value (dark blue line). When this indicator falls below a threshold of 40% we see hazardous spikes of up to 200 μg/m3, which correspond to “unhealthy” levels of PM2.5.
There are not a whole lot of other compelling explanations as to why PM2.5 jumps so dramatically at game time. It’s certainly not due to increased productivity, and it is difficult to conceive of an extraordinary pregame traffic glut that could be accommodated by Santiago’s network of streets and highways, which is already overcapacity. Mass barbecue provides a known mechanism that has a direct analogue: the burning of leña for residential heating, which we know has profound negative impacts on air quality. We therefore conclude that Intendente Orrego was not talking out of his ass and the government’s pleas to limit asados have some basis in reality.
I’ve mentioned “we” several times—we are a group of oddballs from geology, agronomy, and public health who have taken an interest in the theme as a way to distract us from the drudgery of our respective studies. We hope to answer some of the following questions with future work:
- Why do some games result in an asado effect, and other games not? We think that climate plays a part, as well as day of the week (weekday vs. weekend), but the other factor at play is what we term match importance: the relative importance of a particular match to the future success of the Selección Chilena. For instance, the final game of a group stage where the Selección is guaranteed qualification would not be very important (e.g. Chile-Bolivia 2015), whereas any elimination stage should be very important. This is something that depends on a great number of sporting factors, and anyone on the street could give you an idea of match importance, but to define a match importance index that is independent poses a challenge. Right now our agronomist is working on using Google Search indices in the days and hours leading up to the game to evaluate match importance, which shows some promise.
- Which specific air quality signatures are associated with "Asado Events"? Many factors could still potentially produce spikes in PM2.5, so it would be useful to define an "Asado Signature" in PM2.5 and the rest of the airborne contaminants to say with more certainty that spike x was associated with mass barbecue. A critical ratio of PM2.5 / NO2 appears to correlate with asado events, as well as national holidays, but as the public health specialist points out, all this really tells us is when people don't drive. The search continues for a reliable indicator.
- What are the specific public health effects of short-term spikes in PM2.5? Most studies are about health risks of chronic, long-term exposure to PM2.5; few have studied specific effects of short-term extreme events. We are currently (lazily) looking for hospitalization data, that could at very least show if there is an acute public health effect of mass barbecue.
- Do we see this in other countries? Right now we are reaching out to colleagues in Brazil to see if they observe a similar phenomenon, provoked by the burning of wood for barbecues and pizza. This would more convincingly demonstrate this most interesting of teleconnections: that sporting events that take place in another continent can lead to local environmental effects, influenced as well by local culture.
I wouldn't go too far to say that missing out on the 2018 World Cup is a good thing for public health...but hey. Stay tuned to the Crampon Blog for further developments!