Role of ammonia and water vapor on the formation of secondary organic aerosols in alkene/ozone react

Dr. Kwangsam NaBourns College of Engineering¡XCenter for Environmental Research and Technology (CE-CERT), University of California, RiversideAbstractThis study deals with the influence of ammonia (NH3) on secondary organic aerosol (SOA) formation from the ƒÑ-pinene/ozone systems in the dry and humid conditions. The effect of different OH scavengers on SOA formation is briefly described. The aerosol yield differed depending on which OH scavenger was used. Yield was the highest using CO, followed by cyclohexane and 2-butanol. It was found that the number and volume concentrations were quickly increased by 15% and 8%, respectively when NH3 was added after the reaction ceased. An increase in number concentration indicates the formation of new particles resulting from gas-to-particle conversion. Moreover, average size of particles increased from 242 nm to 248 nm. The resulting particles may be ammonium salts formed by the reaction between organic acids and NH3. When NH3 was added to an aerosolized cis-pinonic acid in the chamber reactor, a dramatic increase in both number and volume concentrations of cis-pinonic acid was observed. This is evidence that NH3 drives gas-phase organic acids into condensable salts, leading to elevated SOA formation. Initially present NH3 significantly enhanced aerosol yield in ƒÑ-pinene-ozone reactions, regardless of the presence of water vapor. However, the enhancing effect of NH3 on SOA formation was found to diminish in humid conditions. The degree of the increase in SOA yield in the presence of NH3 was higher in the humid condition than in the dry condition. The role of NH3 on SOA formation in the dry and humid conditions was further explained and discussed in terms of a theoretical modeling study.

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