Aqueous surfaces act as a gateway to absorption and aqueous-phase reaction of gases in the atmosphere. The composition of aerosols varies greatly and is expected to influence the structure of the interface. For example, aldehydes comprise a significant fraction of atmospheric organics and are likely to accumulate at aqueous surfaces. But it is difficult to anticipate their effect on the migration of gaseous species through the interfacial region. Surface organics may act as a barrier to absorption, or they may facilitate uptake via cooperative interactions with absorbing compounds. The surface spectroscopic studies presented here examine the nature of the vapor/water interface during uptake of SO2 to aqueous formaldehyde solutions, elucidating the role of surface species in a multicomponent interfacial system. The results show that the product of the reaction between SO2 and formaldehyde, hydroxymethanesulfonate, shows a surface affinity that is enhanced in the presence of SO2.