Aerosol story gets new angle

US researchers discover role of aromatic acids in particle formation.

Governments around the world may need to toughen up their approaches to reducing emissions from cars and power plants, following a discovery that aromatic acids in vehicle emissions interact with sulfuric acid from the burning of fossil fuels to form tiny particles in the atmosphere. Such atmospheric aerosols have damaging effects on human health, global climate and air quality.

Researchers have long puzzled over how new particles form in the atmosphere. Most of the work in this area has focused on the nucleation of sulfuric acid, but it is commonly recognised that some other component must aid nucleation. Although researchers have been aware that aerosols contain a sizeable amount of organic material, few experimental studies have investigated new particle formation involving organic acids.

A team of US researchers led by Renyi Zhang from the Department of Atmospheric Sciences at Texas A & M University looked at the role that aromatic acids, which can form from the photochemical degradation of aromatic hydrocarbons emitted from cars, play in aerosol formation.

The researchers mixed aromatic acid vapours (such as benzoic acid) with sulfuric acid in an aerosol chamber to produce nanometre-sized particles. The aromatic acids enhanced the nucleation of sulfuric acid and the team’s theoretical calculations suggest that an ’unusually stable’ aromatic acid-sulfuric acid complex forms which encourages particle formation.

The team considers that the work may have major implications for sulfate aerosol formation in polluted areas. Zhang told Chemistry World that the research ’implies that regulatory controls in both automobile VOC [volatile organic compounds] and power plant SO ₂ emissions need to be considered to reduce the aerosol effects on human health, global climate, and even local weather’. He thinks that ’improving the understanding of the formation and transformation of aerosols in the atmosphere is important to help reduce the effects of atmospheric particulate matter at the legislative level’.

Emma Davies