The overall goal of this project is to reduce uncertainties related to the formation, oxidative aging, and cloud condensation nucleus (CCN) activity of organic aerosol particles, thereby providing a more reliable base for modeling and predicting climate change. A unique laboratory setup to characterize the composition, size, morphology, and density of aerosol particles and to measure CCN activity of these particles will be used to characterize and understand secondary organic aerosol (SOA) formation/evolution mechanisms and yields from atmospherically relevant precursor gases oxidized by hydroxyl and hydroperoxyl radicals and ozone. Multi-step heterogeneous oxidation of atmospherically relevant organic compounds will also be studied. The results will provide information necessary to characterize chemical composition of SOA from given precursors and to accurately represent their CCN proclivity.
The principal investigators (PIs) will actively participate in an initiative funded by the Gelfand Family Charitable Trust to mentor science students in four Boston inner city high schools, a program guided by the TSIP concept (Teaching Science through the Inquiry Process). Students will be mentored in small groups and in one-on-one settings with the aim of helping them prepare science fair projects. Two of the schools have science fairs already (Monument High School and The Engineering School). In the other two, working with the teachers and students, the PIs will help organize such fairs. The vehicle for potential science discussions will be current environmental issues with a specific focus on the atmosphere.
Projects Outcomes Report for General Public NSF Award ID 0854916 Small aerosol particles play a significant role in weather and climate. A large fraction of these particles consists of organic compounds that come from reactions between atmospheric hydroxyl radicals (OH) and volatile organic compounds (VOCs) emitted into the atmosphere from anthropogenic and biogenic sources. During the days that the particles remain in the atmosphere, oxidation reactions with OH continue with the aerosol particles and with the organic gases interacting with the particles. As the particles become more oxidized, the properties of the aerosol particles continue to change. The importance of aerosols as climate forcing agents has become evident both through field studies and modeling studies. Organic aerosols, as other aerosols, can affect climate by direct or indirect processes. In the direct process, aerosols alter the atmospheric radiation budget by either absorbing or scattering incoming light depending on their composition and morphology (shape). Absorption reduces the net solar radiative flux to the earth’s surface, while warming the atmosphere in the vicinity of the aerosols. The indirect effects of aerosols occur through changes in cloud properties. It has been demonstrated in both field and laboratory studies that organic aerosols can serve as cloud condensation nuclei (CCN), often as effectively as inorganic sulfate aerosols. An increase in the number of cloud condensation nuclei leads to a larger number of smaller droplets in a cloud. This in turn leads to higher reflectivity for the cloud and enhanced negative solar radiative forcing (i.e. cooling). In addition, field studies have shown that smaller droplets grow less as the cloud develops, decreasing the likelihood of precipitation. On the other hand, large soluble aerosols increase droplet growth and promote precipitation. In our laboratory research program we are systematically studying how CCN and optical properties of organic aerosols of known morphology size and composition (including mixed composition) are affected by controlled transformations via oxidative reactions, and by atmospherically relevant coatings formed by deposition. Experiments are performed under conditions as close as possible to those found in the atmosphere. The results of our work have been published in refereed journals. The quantitative relationships derived from this work are used in models to improve the simulation of impacts by aerosol particles on weather and climate. During the grant period, undergraduate, graduate students and post-doctoral research associates contributed to the research. The participants gained experience in modern experimental techniques and computer data analysis. They are also gained experience in laser optics. They presented regular weekly seminars that provided excellent teaching experience.
