Metropolitan São Paulo needs to control diesel vehicle emissions

Reviews of air quality data from the past 30 years show that the control of emissions from vehicles and factories is working and advocate the use of electric or hybrid buses.

By Maria Fernanda Ziegler  |  Agência FAPESP – Although the numbers are still alarming, and the air quality of the São Paulo metropolitan area is still very poor, the air quality has nonetheless improved in the past 30 years, mainly because of emission controls, according to a review of the air quality data of the mega-city published in Atmospheric Environment.

The study summarizes the results achieved in the Thematic Project “Narrowing the uncertainties on aerosol and climate changes in São Paulo State: NUANCES-SPS,” which was supported by FAPESP until its completion in 2016. Several institutes of the University of São Paulo (USP)t, as well as the São Paulo Environmental Corporation (CETESB), participated in the project.

Despite the growth of the vehicle fleet, a growth of 76% between 2002 and 2012 that reached 11 million vehicles in 2014, the levels of pollutants have fallen in the past ten years, except those of ozone gas and fine particulate matter, both of which are linked to health problems and cognitive disorders, especially in children and the elderly.

“The results are visible. Even with an expanding vehicle fleet, emissions have fallen not just in absolute terms but also in terms of environmental concentrations,” said Maria de Fátima de Andrade, one of the authors of the study, in an interview given to Agência FAPESP.

Nevertheless, alarm bells are still ringing: every year, over 10,000 deaths are closely linked to pollution by particulate matter in metropolitan São Paulo.

“We’ve reached the limit in controlling emissions from light vehicles,” Andrade said. “If the fleet continues to grow as expected, emissions will rise and so will environmental concentrations. The strategy must be to reduce the fleet of circulating vehicles, promote the use of mass transit, and keep developing clean fuels, especially for heavy vehicles like buses, which run on diesel – still a major source of pollution – and can be replaced by electric or hybrid vehicles.”

The study, a collaboration involving researchers from USP’s institutes of Astronomy, Geophysics & Atmospheric Sciences (IAG), Physics (IF), Chemistry (IQ) and Geosciences (IG), as well as its School of Arts, Sciences & Humanities (EACH), has estimated the changes in atmospheric pollutant concentrations in Greater São Paulo since the 1980s, when levels of sulfur oxide (SOx), carbon monoxide (CO), ozone (O3), nitrogen oxide (NOx) and aldehydes (RCHO) were very high. Control of industrial emissions began in the 1980s, with the use of low-sulfur fuels and changes in boiler fuels. At that time, the federal government launched the Proálcool program to foster the use of fuel ethanol from sugarcane.

In the 1990s, concentrations of sulfur fell, and there was a rise in the levels of hydrocarbons, aldehydes and particulate matter. Consequently, in the 1990s, measures were taken to control industrial pollution by sulfur emissions, and a license plate-based traffic rationing rule was introduced. However, there were still high levels of hydrocarbons and particulate matter, owing to rising fuel consumption and fleet expansion, as well as non-compliance with legal emission limits by vehicle owners.

Environmental measurements began showing the effects of light vehicle emission control in the 2000s, particularly because of the introduction in 1986 of the Proconve program to control air pollution by automotive vehicles. Ten years later, it was clear that levels of practically all pollutants except hydrocarbons and particulate matter were falling. According to Andrade, the exceptions were due to continuing fleet expansion, which resulted in growing fuel consumption.

“Control of exhaust emissions was effective, but there was an increase in evaporative emissions, from vehicle crankcases, fuel tanks and lines as well as filling stations, which explains the higher concentrations of hydrocarbons,” Andrade said. “Levels of particulate matter remained high because of delays in implementing phase P7 of Proconve [to control heavy vehicle emissions] as well as [because of] fleet expansion.”

Climate change

Pollution in São Paulo has specific characteristics. The mega-city’s vehicle fleet is large and old, with an average light vehicle age of 9 years and an average truck age of 10 years, compared with the 7 years and 8 years seen in the US and Europe, respectively. The vehicle fuel mix is also different, because a significant proportion of the fleet runs on ethanol or biodiesel.

In a recent study performed as part of the Thematic Project, researchers have shown that light vehicles in São Paulo emit 3.5 times more formaldehyde and acetaldehyde than light vehicles in California (USA). In addition, despite the decrease in hydrocarbon concentrations in São Paulo, current levels are higher than those in other global mega-cities, such as Beijing, London, Los Angeles or Paris.

The analysis of the pollutant levels over the past 30 years also shows that a great deal has changed in terms of both legislation and measurement methods, thus expanding the knowledge of the effects of pollution on the air quality in São Paulo and on public health. 

The study of atmospheric pollution has progressed considerably both here and worldwide, according to Andrade.

“We know a lot more about the importance of urban emissions,” she said. “Inventories of emissions globally now recognize the importance of cities. Previous studies typically ignored local emissions, such as those of the transportation sector, for example. Several initiatives are underway worldwide to quantify the urban contribution more accurately.”

Estimates of atmospheric emissions were previously based mainly on those of developed countries, Andrade noted. “Northern hemisphere inventories mostly estimated vehicle and industrial emissions, while southern hemisphere inventories focused on forest fires,” she said.

The link between local pollution and climate change has also been revisited. “The main strategy ignored the impact of local urban pollution on climate change,” she said. “More recently, however, the approach has changed somewhat. Pollutants emitted locally with an impact on air quality can also influence climate change. Ozone and some types of particulate matter are examples.”

This change has improved the models used to estimate the contributions of cities and mega-cities to atmospheric pollution and climate change. Moreover, it has become clearer that cities will be particularly affected by climate change, not just in terms of floods, droughts and rising temperatures but also via the effects of rising levels of pollutant concentrations in the atmosphere on urban populations.

“For example, ozone levels may rise if the temperature rises, and an increase in humidity will also change the mix of compounds in the atmosphere,” Andrade said.

This process shows that controlling emissions benefits cities in two ways: by improving air quality and by helping to mitigate adverse effects on climate change.

The article “Air quality in the mega-city of São Paulo: Evolution over the last 30 years and future perspectives” (doi: https://doi.org/10.1016/j.atmosenv.2017.03.051) by Maria de Fátima Andrade, Prashant Kumar, Edmilson Dias de Freitas, Rita Yuri Ynoue, Jorge Martins, Leila D. Martins, Thiago Nogueira, Pedro Perez-Martinez and Regina Maura de Miranda can be retrieved from sciencedirect.com/science/article/pii/S1352231017302212.