We employed a MATLAB-based kinetic model (Supporting Information, Section S1) to assess We used a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) from Aerodyne Research 99 to probe the composition of the guaiacol-NO 3 SOA. The amount of nitrogencontaining compounds in the mass spectrum was 15% (Section S2 and Fig. ), consistent with expectations based on previous HR-AMS measurements of SOA generated by reactions of NO 3 with volatile organic compounds. As expected for this reaction, all of the nitrogen-containing compounds identified in the mass spectrometer originated from organic nitrogen compounds. For details, see Section S2.