Atmospheric aerosols affect Earth’s radiative energy. New particle formation (NPF) by gas-to-particle conversion is estimated to contribute to around half of global cloud condensation nuclei. Originally, it was thought that NPF can only occur in the presence of sulfuric acid vapour. However, laboratory experiments have shown that particles can form in the atmosphere from biogenic organic precursors in the absence of sulfuric acid or any other vapour.

Biogenic vapours are predominantly due to isoprene and terpene emissions from vegetation, in particular trees. They occur as a rich and variable mixture which depends on the genotype and phenotype of the plant and its environmental conditions such as stress and predation. Therefore, representing atmospheric biogenic NPF in global models requires experiments that measure the role of each component individually and in a mixture. While the roles of monoterpenes and isoprene have been demonstrated earlier, here we explore how sesquiterpenes (C₁₅H₂₄, represented by β-caryophyllene) influence pure biogenic particle formation and growth under both pristine (low NO) and perturbed (high NO) conditions.

We report pure biogenic nucleation and growth rates measured in the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber from several biogenic components under a range of environmental conditions. We find that sesquiterpenes are extremely efficient precursors for new-particle formation since their ozonolysis results in a high yield of extremely low-volatility organic compounds. A minute concentration of sesquiterpenes added to the biogenic mixture of monoterpenes and isoprene can counteract the isoprene particle formation suppression effect.

Studying pure biogenic nucleation helps understand NPF in unpolluted environments such as rain forests or at high altitudes, as well as in the pristine pre-industrial climate (and possibly future climate as anthropogenic emissions are reduced).

Lubna Dada

Appearances