Date Thesis Awarded


Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)




Rachel O'Brien

Committee Members

Nathan Kidwell

Mike Jabbur

Kristin Wustholz


Organic aerosols in the atmosphere have a large impact on global climate and human health. Understanding the lifetimes and fates of these organics in the atmosphere is imperative for optimizing climate models and characterizing their contributions to net atmospheric warming. The warming and cooling properties of aerosols are related to their abilities to absorb or scatter light. Brown carbon is a type of organic aerosol that is of particular interest due to its ability to absorb light in the visible range. These absorption and scattering properties can change, however, if the aerosols are subjected to photolytic or chemical aging. These aging processes are limiting factors on an aerosol’s atmospheric lifetime.

In the atmosphere aerosols exist in the dry and aqueous phase. Aqueous aerosols may be found in cloud-water systems, where photolytic and chemical aging can still take place. The literature reports characterizations of different secondary organic aerosol (SOA) component lifetimes in these cloud-water systems, but often does not investigate these lifetimes in “dirty” systems where more than one type of SOA molecule exists. This overlooks the potential for interactions between aerosols of different compositions and ages. In this work, we investigate the photolytic lifetimes of 4-nitrophenol under atmospheric cloud-water conditions. We characterize these lifetimes both alone and in a mixed system with a-pinene SOA by analyzing the kinetics of 4-nitrophenol photolysis. The presence of SOA seems to have an important impact on the photolytic lifetimes of 4-nitrophenol, with fresh SOA accelerating the rate of photo-decay and aged SOA slowing it. We hypothesize that OH radicals produced as photo-products contribute to the photo-decay of this brown carbon when in a system with other organic SOA.

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