Nitric oxide can enhance secondary aerosol precursor formation from aromatic carbonyls

Atmospheric oxidation of aromatic carbonyl compounds in urban environments can lead to highly oxygenated organic molecules (HOMs) that are direct precursors to secondary organic aerosols (SOA). Presence of NO x (NO + NO 2 ) is generally assumed to suppress HOM and consequently SOA formation. In this work, experiments with 1 ppm of benzaldehyde, phenylacetaldehyde, and acetophenone show that NO concentrations ranging from 10 ppb to 1 ppm can enhance HOM yields by up to tenfold, with a decreasing trend at above 300 ppb NO. Additionally, HOMs with up to 12 oxygen atoms are observed in sub-second to second timescales, indicating active pathways of rapid oxygen additions following initial oxidation. Quantum chemical calculations are employed to elucidate the oxidation pathways of these carbonyls. The considerable HOM yields and their enhancement in the presence of NO x provide valuable insights into how shifting aromatic and NO x emission trends influence urban air quality and aerosol formation.