Abstract/Summary

Atmospheric aerosols play an essential role in the climate. They are essential to the atmosphere as they help to form clouds and participate in the radiative balance and regulation of terrestrial surface temperature. Organic aerosols originate from natural and man-made sources. Meat cooking is considered an important contributor of a variety of organic compounds in the atmosphere, such as fatty acids. Oleic, linoleic and palmitoleic acids are the most commonly found long-chain unsaturated fatty acids in urban environments. These fatty acids contribute considerably to the aerosol fraction due to the reactions that they undergo, such as ozonolysis, which yields aerosols that have a notable impact on climate and health. It is known that the presence of water in variable relative humidity environments may affect the reaction of ozonolysis of unsaturated fatty acids since both, the carboxylic acid and the products formed may retain water at the surface, increasing the residence time of dissolved ozone at the surface and affecting the reactive uptake coefficient of ozone. The chemistry involved in the reactions of atmospheric aerosols still remains poorly understood. In this study, Raman acoustic levitation was used to assess the effect of ozone concentration, relative humidity, droplet size and the presence of surfactants, on the ozonolysis of fatty acids. It was found that droplet size affected the uptake coefficient, whereas relative humidity had a variable effect in the uptake coefficient depending on additional factors, such as ozone concentration and droplet diameter. The presence of surfactants such as sodium oleate decreased the uptake coefficient of ozone and induced a phase transformation of the levitated droplets, even under high relative humidity. Palmitoleic and linoleic acids showed more reactivity compared to oleic acid. Products were analysed by headspace solid-phase micro-extraction (SPME) coupled to gas chromatography mass spectrometry (GC–MS). A mechanism of ozonolysis of palmitoleic acids was proposed, and some products were verified to be formed from the reactions. Products of ozonolysis of fatty acids were identified.