Wood and charcoal burning may contribute to atmospheric pollution in São Paulo

Study suggests control of emissions from unregulated and underestimated sources such as wood-fired pizza ovens and barbecues would improve air quality in metropolitan area.

By Elton Alisson  |  Agência FAPESP – Air quality in metropolitan São Paulo, Brazil, can be improved by controlling emissions of pollutants from unregulated and underestimated sources such as wood and charcoal burning in pizzerias and steakhouses, among other measures.

This assessment is part of a study conducted by researchers at the University of São Paulo’s Institute of Astronomy, Geophysics & Atmospheric Sciences (IAG-USP) in collaboration with colleagues at the University of Surrey in the United Kingdom, North Carolina State University in the United States, and the Federal University of Minas Gerais (UFMG) and Federal Technological University of Paraná (UTFPR) in Brazil.

Resulting from a project conducted under the aegis of the University Global Partnership Network (UGPN) – in which some of the world’s leading universities collaborate on innovative solutions to world problems based on shared research expertise – and a Thematic Project linked to FAPESP’s Research Program on Global Climate Change (RPGCC), the study was published in the journal Atmospheric Environment.

“Although most emissions of pollutants in metropolitan São Paulo come from the vehicle fleet, other sources should also be considered, such as sugarcane and other biomass burning in agricultural areas of São Paulo State, forest fires in Amazonia, wood-fired stoves in pizza parlors and charcoal-burning barbecue restaurants,” said Maria de Fátima Andrade, a professor at IAG-USP and co-author of the study, in an interview with Agência FAPESP.

“However, it’s important to note that air quality in metropolitan São Paulo won’t improve significantly without a reduction in the vehicle fleet as well as effective control of emissions from motor vehicles.”

The vehicle fleet is the main source of air pollution in the metropolitan area, she stressed, especially particulate matter – very fine particles of solids or liquids suspended in the air.

Emissions of pollutants by new vehicles that join the fleet have decreased in recent years thanks to a number of measures designed to control emissions in accordance with more restrictive standards.

There is insufficient information on the extent to which other sources that involve burning of biomass (firewood, charcoal and waste, among others) contribute to total emissions and their impact on health, according to Andrade.

“We don’t know exactly what proportion of total emissions comes from these sources, and indeed from others that are even more significant, such as industrial plants,” she said. “They need to be described in far greater detail, and their impact on the atmosphere needs to be properly assessed.”

Emissions from pizza ovens

To estimate the contributions of different sources to total emissions of pollutants generated by biomass burning in metropolitan São Paulo, the researchers at IAG-USP, in collaboration with other research groups in Brazil and abroad, collected data on several sources as part of the Thematic Project supported by FAPESP.

As part of the UGPN project, meanwhile, they studied chemical transportation to the metropolitan area of aerosols generated by forest fires in Amazonia and pre-harvest burning of sugarcane plantations in São Paulo State to eliminate leaves. Their aim was to distinguish these sources from local emissions such as those generated by wood and charcoal burning.

“When emissions of pollutants from biomass burning in metropolitan São Paulo are measured, it’s always assumed they come from the transportation of particles emitted by sugarcane trash burning outside the metropolitan area, for example, and hence coming from a long way away,” Andrade said.

“But actually, a large proportion of the mass of particles containing carbon compounds may come from biomass burning inside the city: from wood-fired pizza ovens and charcoal-burning barbecue restaurants, for example.”

A masters dissertation produced by Francisco Daniel Mota Lima while completing the graduate program in sustainability at the University of São Paulo’s School of Arts, Sciences & Humanities (EACH-USP) under the supervision of Regina Miranda confirmed this hypothesis.

The study demonstrated that biomass burning by pizzerias in São Paulo City is a source of air pollution.

According to the estimates in the study, São Paulo has more than 8,000 pizzerias, which produce 1.5 million pizzas a day, more than any other city in the world except New York. Approximately 80% of these establishments burn wood, especially eucalyptus.

The average amount of wood burned by a pizza parlor is 48 metric tons per year (mty), so the total is estimated at 307,200 mty. The authors say more than 7.5 hectares of eucalyptus forest are being burned every month by pizzerias and steakhouses.

Moreover, all this wood and charcoal burning results in daily emission into the atmosphere of 321 kg of fine particles with a diameter of less than 2.5 microns, considered the most hazardous to human health. It also disturbs the atmospheric radiative balance.

“Even though the restaurants are burning tons of wood or charcoal and causing a lot of pollution, they only account for approximately 3% of the total daily emissions of pollutants generated by vehicles and industry, which is very little relatively speaking,” Andrade said.

According to the authors of the study published in the journal Atmospheric Environment, however, emissions from wood and charcoal burning by pizzerias and barbecue joints are not scientifically quantified, so their share in total emissions from biomass burning in metropolitan São Paulo is unknown and they are left out of the official greenhouse gas inventories.

For example, the energy balance reports published by the São Paulo State Government make no distinctions for firewood and charcoal, the leading consumers of which are pizzerias and steakhouses.

Because these emissions occur in the evening, when atmospheric conditions are more stable and the particles disperse less, and because pizzeria and barbecue chimneys are close to ground level, the effect of such emissions is expected to be far higher than the effect of industrial emissions from tall chimneys, especially during cold months with stable atmospheric conditions, according to the study.

“On average, these emissions may not be so significant as a percentage of total emissions from biomass burning in metropolitan São Paulo because they’re more diluted,” Andrade said. “But if we look at specific times, such as evenings and cold months, they contribute more because they’re more concentrated,” Andrade said.

Other sources

The authors of the study say more research is needed to quantify emissions of particulate matter by pizzerias and grills burning wood and charcoal, as well as other unaccounted sources both inside and outside metropolitan São Paulo, and to calculate their contribution to total emissions in quantitative assessments of the city’s air pollution.

The other unregulated and unaccounted sources include construction and demolition of buildings, maintenance and repair of street surfaces, domestic waste and biomass burning in outlying suburbs, and pollutants blown in from industrial activities and sugarcane trash burning outside the metropolitan area, as well as forest fires in Amazonia.

A reduction in emissions of pollutants by these sources would improve air quality and help protect human health, the authors say. In Delhi, India, they note, it is proposed that restaurants seating more than ten people should replace coal with electricity or gas. The city also burns a great deal of firewood, so this measure is expected to result in a reduction of approximately 67% in emissions of particles with diameters of 10 and 2.5 microns.

With 21 million inhabitants, metropolitan São Paulo is the fifth most populous urban region in the world and the second most populous in Latin America. Hence the importance stressed by the authors of assessing the impact of all sources of air pollution including biomass burning. “Any benefits in terms of a reduction in the concentration of pollutants will be very significant because of the impact on a population of 21 million,” Andrade said.

The study “New directions: from biofuels to wood stoves: The modern and ancient air quality challenges in the megacity of São Paulo” (doi: 10.1016/j.atmosenv.2016.05.059) by Prashant Kumar and Maria de Fatima Andrade et al. can be read by subscribers to Atmospheric Environment at sciencedirect.com/science/article/pii/S1352231016304071.