Laboratory Studies of New Particle Formation from Ozonolysis of Sesquiterpenes

Secondary particles formed by gas-to-particle conversion contribute significantly to cloud condensation nuclei (CCN) production, thus affecting cloud formation and global climate. Several species including sulfuric acid, ammonia, amines, organic acids were found to be efficient precursors for atmospheric nucleation. Recently highly oxidized molecules (HOMs) have been identified as key components for new particle formation in smog chamber experiments and field measurements. Many of those molecules are products from ozonolysis of biogenic hydrocarbons. Here we present results from laboratory measurements of new particle formation from ozonolysis of several sesquiterpenes including beta-caryophyllene, alpha-humulene, and alpha-cedrene. The experiments were performed in a continuous flow tube reactor with a reaction time of about one minute. Several advanced online instruments were employed to measure gaseous species and nanoparticles, including a Chemical Ionization Mass Spectrometry (CIMS) that measures gaseous species in a mass range of 10-1000 amu and particle sizers that measure particle number size distributions (PNSD) of nanoparticles in a diameter range of 2-500 nm. We also collected filter samples of particles formed from the oxidation for off-line HPLC and IC analysis. We found that the HOMs were highly correlated with concentrations of newly-formed particles. We then modeled nanoparticle formation in the flow reaction system using the measured HOMs and the PNSD. Possible pathways leading to the formation of the HOMs and implication of the ozonolysis of sesquiterpenes will be discussed.