Relative Humidity Impact on Organic New Particle Formation from Ozonolysis of α- and β-Pinene at Atmospherically Relevant Mixing Ratios

The impact of relative humidity (RH) on organic new particle formation (NPF) from ozonolysis monoterpenes remains an area active debate. Previous reports provide contradictory results indicating both depression and enhancement NPF under conditions moderate RH, while others do not indicate a potential impact. Only several have suggested that the effect may depend absolute mixing ratio precursor volatile compound (VOC, ppbv). Herein we report RH dark α- β-pinene at ratios ranging 0.2 to 80 ppbv. We show enhances (by factor eight) lowest α-pinene ratio, with very strong dependence 4 22 At higher ratios, plateaus, resulting modest decreases in NPF. In case β-pinene, is enhanced low due combination chemistry, accelerated kinetics, reduced partitioning semi-volatile oxidation products particulate phase. Reduced would limit growth, permitting increased gas-phase concentrations semi- low-volatility products, which could favor