8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P6.6Fri 911:10-14:00Water adsorption around oxalic acid aggregates: amolecular dynamics simulation of water nucleation onorganic aerosolsMária Darvas 11 ELTE University, Pázmány stny. 1/a, H-1117, Budapest, HungaryA vast amount of volatile organic compounds (VOCs) are emitted on a daily basis into the atmospherefrom both natural and anthropogenic sources. They are now known to be essentialcomponents of tropospheric chemistry as result of their aerosol forming ability. Aerosols formedby dicarboxylic acids, such as oxalic acid, comprise a significant percentage of the total organicmatter of the atmosphere. Such organic aerosols, having free carboxyl and hydroxyl groups at theirsurface can form hydrogen bonds with other H-bonding species, such as waters, present in the atmosphere,thus they are suspected to be efficient cloud condensation nuclei. However, while thepotential of organic aerosols to act as CCN for water clouds is well-established, their influence onice clouds in the upper troposphere is less well known. Due to the potential impact of aerosols onEarth’s atmosphere, a thorough understanding of their phase transitions under atmospheric conditionsis strongly needed, especially when they are in contact with water molecules. In this work, wepresent a computer simulation study of the p, T phase diagram of binary oxalic acid/water aerosolsof different water compositions to shed light on the complexity and composition dependence ofthe phase transitions in the aerosol phase. We discuss in details the observed phase transitionsin the atmospherically relevant temperature and pressure range, and finally we give a qualitativepicture of thermodynamic reasons underlying the phase behavior, discussing in detail the effect ofpressure, temperature and composition.6