Effect of Relative Humidity on Organic Vapor Condensation and New Particle Formation

New particle formation from oxygenated organic vapors is an important source of secondary organic aerosols, which have significant implications for both human health and climate change. This process is thought to be facilitated at higher relative humidity (RH) by enhanced partitioning of more volatile species into the particle phase. However, high RH is often associated with a high condensation sink and low solar radiation intensity, so new particle formation events have been preferentially observed in low RH environments. In this presentation, we investigate the interplay between new particle growth by oxygenated organic vapor condensation and coagulation scavenging by pre-existing particles across a range of tropospheric RH levels using an aerosol microphysical model constrained by chamber experiments at CLOUD. These results provide a quantitative understanding of the conditions that favor particle formation and improve parameterizations for the RH dependence of organic particle formation in atmospheric models.