Characterization of secondary organic aerosol (SOA) formation and toxicity from α-pinene photo-oxidation under effects of nitrogen oxides (NOx) and ammonia (NH3)

The chemical and bioreactivity properties of secondary organic aerosol (SOA) from α-pinene photooxidation in the presence of atmospheric gaseous precursors (nitrogen oxides and ammonia) conditions were characterized to evaluate the corresponding cell toxicity of these SOA by-products. The average concentrations between these SOA masses under hydroxyl radical (OH) initiated photo-oxidation in the presence and absence of NH3 condition showed statistically significant differences (paired t-test; p < 0.005). The mass spectra of SOA formed under different conditions demonstrated continuous existence of nitrogenous organic compounds under different NOx exposure conditions and fragments were characterized as the mass-to-charge ratio (m/z) of 43 and 44 are the most significant peaks in the spectrum. The unit-mass-resolution of m/z 43 signal intensity exceeded that of m/z 44, implying possible less oxygenated organic material at lower loadings. The estimated nitrogen-to-carbon (N/C) ratio is an order of magnitude lower than oxygen-to-carbon (O/C), highlighting the dominance of oxygen among organic heteroatoms in organic aerosol. The inflammatory responses and correlation coefficients (determined by IL-6 and DCFH) were higher in the presence of NH3, suggesting the possible roles of NH3 in the inflammatory responses exacerbation and increase of reactive oxygen species generation. The results can potentially be used to relate with particle pollution exposure to a variety of respiratory health effects analysis.