Influence of NO₂ on secondary organic aerosol formation from ozonolysis of limonene

Abstract. Limonene has a strong tendency to undergo ozonolysis to form semi-volatile and low-volatility compounds that contribute to secondary organic aerosols (SOAs) both outdoors and indoors. The influence of NO₂ on SOA formation from ozonolysis of limonene has been evaluated using chamber experiments and the Master Chemical Mechanism (MCM) coupled with a gas-particle partitioning model in this work. A series of 21 indoor chamber experiments were carried out with or without NO₂ under different [O₃]₀ / [VOC]₀ ratios, and these experimental data were compared with the model simulations. Agreement in SOA yields was observed between the experimental observations and model simulations under varying conditions. Generally, SOA mass yields are positively dependent on [O₃]₀ / [VOC]₀ without the presence of NO₂. However, the introduction of NO₂ leads to a more complicated change in SOA yield, which is shown to be related to initial [O₃] / [VOC] ratios. When [O₃]₀ / [VOC]₀ > 2, the introduction of NO₂ results in an increase of SOA yield in the range of NO₂ studied in this work; whereas a weak negative effect was found for SOA formation according to the introduction of ~ 250 ppbv NO₂ under [O₃]₀ / [VOC]₀ < 2 conditions. It was suggested that the effect of NO₂ on SOA formation yields from limonene ozonolysis is related to the competition between O₃- and NO₃-initiated oxidation of limonene as well as the competition between RO₂ + HO₂ and RO₂ + NO₂ (or NO₃). Analysis of aerosol chemical composition with Fourier-transform infrared spectroscopy (FTIR) and modeling further confirmed that the formation of peroxy acyl nitrates (PANs) and organic nitrates plays an important role in aerosol particle formation from limonene ozonolysis at the presence of NO₂. The findings here indicate that accurately constraining SOA yields from NO₃ oxidation is essential to evaluate the influence of NO₂ on SOA formation in some real atmosphere, for example, regions with both biogenic and anthropogenic influences.