Detailed insight into formation of atmospheric particulate matter
Monoterpenes are the principal source of secondary organic aerosol (SOA) to the atmosphere. They are emitted from a multitude of plant species, for example, the common coniferous evergreen trees such as pine and spruce.
“The rapid atmospheric oxidation of monoterpenes leads to highly oxygenated organic molecules (HOM) as reaction products, which readily condense onto smallest of the atmospheric particles, thus forming SOA mass. The least volatile fraction has been even seen to form particles by its own, yet this is still to be verified from ambient measurements,” says Matti Rissanen, Assistant Professor in Experimental Aerosol Science at Tampere University.
In this research, the structures of the highly oxidized peroxy radicals forming HOM compounds, and their aggregation products were inspected by a technique able to retrieve structural information for the very first time. The aggregation products, present in miniscule concentrations, are especially important for particulate matter formation.
The research constrains the structures and formation pathway of several HOM-RO2 radicals and dimers produced from monoterpene ozonolysis, a prominent atmospheric oxidation process. In addition to providing insights into atmospheric HOM chemistry, this study debuts online tandem MS analyses as a unique approach for the chemical characterization of reactive compounds, e.g., organic radicals.
"Overall, our findings advance the understanding of atmospheric radical chemistry, which can help constraining model representation of autoxidation pathways and dimer formation kinetics," Matti Rissanen sumps up.
The online approach employed in the research can be readily applied to, and is beneficial for, the investigation of short-lived or labile organic compounds in the gas phase present in low concentrations, demonstrably organic radicals that are otherwise inaccessible by offline techniques.
Read the full article Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry published in Nature Communications.