Water Uptake of Monoterpene Aerosol Mixtures: Towards a Central Value

Bret Hatzinger, Ziheng Zeng, Tim Raymond, DABRINA DUTCHER, Bucknell University

     Abstract Number: 484
     Working Group: Aerosols, Clouds and Climate

Abstract
Understanding secondary organic aerosol (SOA) properties is essential in understanding cloud formation, which represents a significant uncertainty in the context of global climate modeling. Monoterpenes are a class of semi-volatile organic compounds (SVOCs) of both biogenic and anthropogenic origins, emitted into the atmosphere. These compounds, when oxidized, contribute to the formation of SOA. It has been found that half of all total fine organic aerosol can be attributed to monoterpene oxidation. The resultant aerosol particles may also act as cloud condensation nuclei and contribute to cloud growth. Understanding the water uptake ability, or hygroscopicity, of these compounds improves our knowledge of their radiative effects, which can be used to improve climate models. Given that the SOA terpene precursors rarely occur in the atmosphere in isolation, an understanding of their group hygroscopicity will prove at least as valuable as any measurements with single species pre-cursors. To this end, the hygroscopcity of aerosols created from the oxidation of 12 different monoterpenes was measured using a cloud condensation nuclei counter (CCNC) and scanning mobility particle sizer. A single parameter hygroscopicity (κ) value for the aerosol products from each compound was determined and then the compounds were combined in various mixtures. A span of mixture types, from similar (high/high) to contrasting (high/low) in value were analyzed. While not every possible combination was chosen for experimentation, mixtures were intentionally selected so as to provide a wide base of meaningful data. Preliminary results show that as more SOA precursors are introduced into the reaction mixture, κ values trend towards a central value, approximately 0.14.