Effects of NOx and NH3 on the secondary organic aerosol formation from α-pinene photooxidation

Understanding the effects of mixed anthropogenic pollutants on the photooxidation of volatile organic compounds (VOCs) is essential for unraveling the formation pathways of secondary organic aerosols (SOA). Yet, it remains a highly challenging experimental target owing to the complexities in the precise measurement of molecular compositions of products and number/mass concentrations of particles as a function of pollutant concentration in the ambient atmosphere. Here, a series of well-defined chamber experiments were performed to explore the effects of NOx x and NH3 3 on the SOA formation from photooxidation of the most abundant monoterpene, alpha-pinene. The results indicate that the suppression effect of NO and NO2 2 on the alpha-pinene photooxidation shows monotonous and parabolic trends, respectively. The presence of NH3 3 enhances particle number concentrations during the alpha-pinene + NOx x photooxidation by participating in reactions with organic acids. New compounds, including organic peroxides, esters, organic nitrates, and peroxyacyl nitrates, are observed at molecular weight (MW) = 166, 173, 217, 231, 280, 282, 304, and 410 through threshold photoionization making use of a recently constructed vacuum ultraviolet free electron laser in positive ion mode. The molecular structures and formation paths of these species are speculated, which advance the category of VOC oxidation products. Our study provides significant understanding of the influence of NOx x and NH3 3 on the VOC photooxidation, which can be utilized to establish predictive SOA formation networks and to improve atmospheric models.