Heterogeneous Reaction of Peroxyacetyl Nitrate on Real-World PM 2.5 Aerosols: Kinetics, Influencing Factors, and Atmospheric Implications.

The formation and decomposition of peroxyacetyl nitrate (PAN), an important atmospheric nitrogen oxide reservoir, can impact the level and cycling of free radicals and nitrogen compounds in the atmosphere. PAN sinks are poorly understood, highlighting the importance of elucidating the heterogeneous reaction of PAN on aerosol surfaces. Here, we report for the first time the uptake behavior, kinetics, and potential mechanism of PAN uptake on real-world aerosol PM 2.5 using a flow tube system. The uptake coefficients (γ) of PAN increased non-linearly from (1.5 ± 0.7) × 10 -5 at 0% relative humidity (RH) to (9.3 ± 2.0) × 10 -5 at 80% RH. The γ decrease with increasing initial PAN concentration is consistent with the Langmuir-Hinshelwood mechanism. Organic components of aerosols may promote heterogeneous loss of PAN through redox reactions. Higher γ occurs with higher water content, lower pH, and lower ionic strength in the aqueous phase of aerosols. The present study suggests that heterogeneous reaction of PAN on ambient aerosols plays a non-negligible role in the atmospheric PAN budget and provides new insights into the role of PAN in promoting atmospheric oxidation capacity during hazy periods with cold and wet weather conditions.