Editorial Feature

Measuring Ultrafine Particle Levels Within the Atmosphere from Ethanol and Gasoline

Researchers at the Northwestern University’s Department of Chemistry in collaboration with National University of Singapore’s Department of Economics and University of São Paulo recently published a paper in nature communications about the influence of gasoline and ethanol use in the amount of ultrafine particle levels in São Paulo’s atmosphere.

Alberto Salvo’s team found that the number of ultrafine particles released in the atmosphere were significantly lesser than the number ultrafine particles released with gasoline use, while the concentration of larger particles remained statistically insignificant in the São Paulo’s atmosphere1.

The emissions from the vehicles, including larger particles measuring up to 2.5µm and ultrafine particles measuring below 100 nm, are the major contributors of urban air pollution. Even though environmental protection agencies in US and other countries regulate the PM2.5 which is a measure of particulate matter below 2.5µm, the concentration of ultrafine particles (<100 nm) is not regulated1,2. Due to their particle size, these ultrafine particles can get deeper into the lungs, posing a grave health risk to the public.

This group of Researchers performed a regression analysis of consumer behavior, aerosol particle size, traffic and meteorological data from January 2011 to May 2011, during which the consumers made a major fuel switch between ethanol and gasoline due to the fluctuations in ethanol prices1,2.

Even though the study was primarily based on São Paulo’s pollution, other north American cities including Chicago share a similar air chemistry2.  For the first time, this group of Researchers assessed the variation in the concentration of the particulate matter along with particle size distribution in ambient air in a major metropolitan area undergoing a period of major fuel shift from ethanol to gasoline. Aerosol size distribution (between 7 – 800 nm), mass concentration measurements for black carbon (BC) and PM2.5 were evaluated by econometric method in this research to study how fuel prices impact ambient particle levels in urban São Paulo, which is a home for 20 million people and 6 million passenger cars1.

A two-step multivariate regression model based on the price induced shifts in consumer fuel choice and the impact of this choice between ethanol Vs gasoline on ambient air was performed to find any correlation1. The results revealed that the number of ultrafine particles measuring less than 50 nm increased by one third during the time when consumers used gasoline during the ethanol price hike, while the number of these ultrafine particles went down when the consumers switched back to ethanol use with the reduction of ethanol price.

This suggested a tight correlation between the fuel choice and the ultrafine particles in the air1. Whereas, the number of larger particles in the environment of urban São Paulo did not change significantly during the period of fuel switch.

The current research also revealed that the concentration of nanoparticles rise jointly with the gasoline use from January to April and decreased jointly through May during the flex-fuel fleet. However, the increase in ethanol use resulted in an increase in concentrations of ozone1. The use of gasoline over ethanol during the ethanol price hike did not significantly affect the BC mass concentration, PM2.5 mass concentration and PM100-800 nm1. Furthermore, a positive and significant correlation exist between the particle levels measuring between 7-100 nm with gasoline use during peak hours of morning travel, while there is no statistically significant difference in the larger particles during this period1.

Based on the results put forward by this study, there is a need to invest more money and resources into understanding and monitoring these ultrafine particles in the environment to prevent the associated health risks to the public2. The Researchers suggest that the environmental protection agencies should weigh the benefits of decrease in ultrafine particles against the increase in ozone concentrations with the ethanol use2.

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  1. “Reduced ultrafine particle levels in Sao Paulo’s atmosphere during shifts from gasoline to ethanol use” A. Salvo, J. Brito, et al. Mature Communiations. (2017). DOI: 10.1038/s41467-017-00041-5.
  2. “Tiny particles will increase in air with ethanol-to-gasoline switch” – Northwestern University

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