Uptake of Gaseous Alkylamides by Suspended Sulfuric Acid Particles: Formation of Ammonium/Aminium Salts

Amides represent an important class of nitrogen-containing compounds in the atmosphere that can in theory interact with atmospheric acidic particles and contribute to secondary aerosol formation. In this study, uptake coefficients (γ) of six alkylamides (C₁ to C₃) by suspended sulfuric acid particles were measured using an aerosol flow tube coupled to a high resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS). At 293 K and < 3% relative humidity (RH), the measured uptake coefficients for six alkylamides were in the range of (4.8–23) × 10^–2. A negative dependence upon RH was observed for both N-methylformamide and N,N-dimethylformamide, likely due to decreased mass accommodation coefficients (α) at lower acidities. A negative temperature dependence was observed for N,N-dimethylformamide under < 3% RH, also consistent with the mass accommodation-controlled uptake processes. Chemical analysis of reacted sulfuric acid particles indicates that alkylamides hydrolyzed in the presence of water molecules to form ammonium or aminium. Our results suggest that multiphase uptake of amides will contribute to growth of atmospheric acidic particles and alter their chemical composition.