The impact of CO on secondary organic aerosols formed from the mixture of α -pinene and n -dodecane

Secondary organic aerosol (SOA) formation is strongly influenced by atmospheric conditions. Achieving atmospheric relevance in chamber experiments is essential for understanding and predicting the impacts of SOA on air quality and climate. However, many chamber studies are conducted under simplified conditions or with a single SOA precursor. Here, we investigated the impact of CO on SOA particle mass yields and chemical composition from α-pinene (a biogenic volatile organic compound, VOC), n-dodecane (an anthropogenic intermediate-volatility organic compound, IVOC), and their mixture in the presence of nitrogen oxides (NOx=NO+NO2) in the Manchester Aerosol Chamber (MAC) using online measurements. The results show that the influence of CO differed between single- and mixed-precursor systems. In the single-precursor systems, CO significantly suppressed SOA particle mass yields, whereas no such suppression was observed in the mixture. Moreover, compared with the single-precursor systems, CO exerted a diminished impact on the organic peroxy (RO2) radical reaction pathways in the mixture, with the extent of this change differing between α-pinene and n-dodecane. These findings highlight the importance of accounting for atmospheric complexity in laboratory studies.