New research from Khalifa University reveals how surface oxygen groups affect the reactivity of soot particles, providing insights to the chemistry of these particles and their potential environmental impact.
Researchers from Khalifa University have investigated the role of oxygenated surface functional groups on the reactivity of soot particles. Using various analytical techniques, they found that the presence of these groups increased the soot particle reactivity with other chemical species found in the atmosphere. This discovery could have important implications for understanding the formation of secondary pollutants in the atmosphere, such as secondary organic aerosols, which are formed through reactions between soot particles and other chemical species.
Dr. Prabhu Azhagapillai, Research Scientist, Dr. Mirella Elkadi, Associate Professor of Chemistry, Dr. Abhijeet Raj, Associate Professor of Chemical Engineering, and Dr. Mohamed Ibrahim Hassan Ali, Associate Professor of Mechanical Engineering, published their results in Combustion and Flame.
Soot particles are a type of air pollutant produced by the incomplete combustion of fossil fuels and biomass.
“During incomplete combustion of fuels, particulate matter or soot particles are formed, made up of nonvolatile, elemental, or stable carbon layers with attached hydrocarbons,” Dr. Ali said. “They are harmful for human health and the environment, and they can react with other species in the atmosphere.”
This reactivity can be advantageous for capturing soot escaping with the exhaust gas from diesel engines, but when soot particles react with other chemicals in the atmosphere, such as nitrogen oxides and sulfur dioxide, they can form secondary pollutants such as ozone. Ozone is a major component of smog and can have negative effects on human health and the environment.
These reactions occur because the oxygenated surface functional groups act as reaction sites for other chemical species. Beyond nitrogen oxides and sulfur dioxide, the functional groups can also react with atmospheric moisture, which can lead to the formation of acidic compounds. Additionally, the reactivity of soot particles can also impact their deposition and transport in the atmosphere. Soot particles that are more reactive may deposit more quickly onto surfaces, which can impact air quality and human health in urban areas.
The presence of these functional groups on the surface of the soot particles is influenced by a number of factors, including the combustion conditions under which the soot particles are formed. For example, soot particles formed under fuel-rich conditions tend to have more oxygenated functional groups on their surface than those formed under fuel-lean conditions. These functional groups are typically oxygen-containing groups, such as carbonyl, hydroxyl, and quinone groups.
The researchers found that the presence of certain oxygenated surface functional groups on the soot particles, specifically carbonyl and quinone groups, can increase their reactivity.
“Our oxidation experiments revealed that the presence of oxygenated functional groups can enhance soot reactivity by reducing the required activation energy for oxidation, but when the oxygenated groups are lost by the progress of oxidation, the activation energies of all samples were very similar with no clear trend, indicating no long-lasting effect of the presence of oxygenated groups,” Dr. Ali said. “Thus, a soot sample with a high concentration of oxygenated groups may show a high reactivity during the initial period of oxidation, but such groups may not significantly affect the overall reactivity of soot particles.”
The reactions between soot particles and other chemical species can affect the composition and properties of the atmosphere, which can be harmful to human health and the environment. Understanding the reactivity of soot particles and the role of their surface chemistry is important for developing effective strategies to mitigate air pollution and its impacts.
12 April 2023