Traces of the total ion count for the acetone peak and the acetone-water cluster peak as a function of time display the enhancement in acetone during the boiling of the SOA (Fig. ). As soon as the catechol SOA sample was introduced to the heated cell (at 1800 s), the total ion signal and the acetone signals rapidly increased followed by a slow decay. The decay of the total ion signal and the acetone signals is likely due to the decay of acetone available to evaporate.