Influence of NH₃ on secondary organic aerosols from the ozonolysis and photooxidation of Α-pinene in a flow reactor

This study presents detailed characterizations of a newly-developed flow reactor including (1) residence time distribution measurements, (2) relative humidity (RH) and temperature control, and (3) OH radical exposure range (i.e., atmospheric aging time). Hydroxyl (OH) radical exposures ranged from 8.20 × 10¹⁰ to 7.22 × 10¹¹ molecules cm⁻³ s (0.5–4.9 d of atmospheric aging). In this study, the effects of NH₃ gas on the secondary organic aerosol (SOA) formation of α-pinene by dark ozonolysis and photooxidation were investigated using the newly-developed flow reactor. For both dark α-pinene ozonolysis and photooxidation, higher SOA yields were observed in the presence of NH₃ than in the absence of NH₃. At RH of ∼50%, the SOA yield for ozonolysis and photooxidation in the presence of NH₃ increased by 23% and 15% relative to those in the absence of NH_3. Similar effects were observed at lower and higher RH conditions. Fourier transform infrared spectroscopy analysis confirmed the presence of nitrogen-containing functional groups in SOA formed in the presence of NH₃. The α-pinene SOA formed in the presence of NH₃ showed higher absorption and fluorescence for UV-visible radiation than those formed in the absence of NH₃.