Enhanced reactive uptake of nonanal by acidic aerosols in the presence of particle-phase organics

An electrodynamic balance was used to examine the effect of the presence of particle-phase organics on the acid-catalyzed reactive uptake of nonanal (NL) vapor. Uptake experiments were conducted by using sulfuric acid (SA) particles, oleic acid/SA (hydrophobic), and levoglucosan/SA (hydrophilic) mixed particles with 6 ppm (approximately) gas-phase NL at about 3% relative humidity. SA reacted with the mixed organics prior to NL uptake to form organic products, denoted as OleA*and Levo*, and with NL to form hydrophobic NL*(particle-phase organics). Fresh SA particles had small mass increases (5%-13%) at the start of NL exposure (0-40 min) even though they are highly acidic. However, OleA*/SA mixed particles of about 30-70 wt% of OleA*took up NL swiftly during the first 40 min. For example, the mass increase of a 33 wt% OleA*particle jumped to 120%. As the organic product, NL*, accumulated, the uptake rate of SA particle increased and the mass increase surged to 150% at 100 min. Afterwards, the mass increase started to level off which yielded a sigmoid uptake curve. For OleA*/SA particles, the uptake rate gradually slowed down resulting in physical-absorption-like uptake kinetics. The physical uptake of NL by a pure OleA*surrogate was negligible (