The goal of this research is a better understanding of aerosol formation processes in the lower troposphere. Laboratory studies of aerosol nucleation by sulfuric acid in the presence of ammonia and organics will be carried out. The effect of oxygenated organics on nucleation will be investigated. Nucleation rates of gaseous sulfuric acid and organics will be determined as a function of organic functional group, carbon chain length, relative humidity, and temperature. The question of whether atmospheric nucleation takes place in the absence of sulfuric acid will be investigated. Long-term, simultaneous in-situ measurements of aerosol size distributions and sulfuric acid at Kent, OH will also be performed. The measured nucleation rates, as well as the information on how organics affect nucleation, will be useful for global models that attempt to predict aerosol and cloud abundances on regional and global scales. The education plan consists of four activities: (1) Development of an atmospheric chemistry research module (to measure solubility of atmospherically relevant organic compounds) for students at 15 Ohio universities, (2) Mentoring of underrepresented groups in science, first generation college students, and women, (3) Teaching atmospheric chemistry for high school students in Upward Bound Pre-College programs, and (4) Updating "Chemistry in the World," an undergraduate chemistry course for non-science majors including elementary and middle school education majors.
Intellectual Merit: Nucleation is a gas to particle process in which solid or liquid particles form directly from gas phase species. Global aerosol models predict that nucleation can contribute to up to 55% of the global production of cloud condensation nuclei (CCN). The current nucleation theories contain high uncertainties even over many orders of magnitude, because these theories are not rigorously tested by experiments. Under the support of this NSF grant, we have conducted observations of aerosol nucleation in the laboratory and in the field, to provide experimental data that can be used to reduce uncertainties in nucleation theories and better understand the particle and CCN formation processes in the atmosphere. Sulfuric acid-water-ammonia ternary homogeneous nucleation is one of the most important atmospheric multicomponent nucleation systems. Especially in the eastern U.S., new particle formation has been typically explained by this process. But there is a large whole in the literature on laboratory observation data on this nucleation system. Our laboratory observations show that nucleation enhancement factors by ammonia are linearly proportional to ammonia concentrations and exponentially decrease with increasing sulfuric acid concentrations and relative humidity. These results can be directly used in the nucleation theories to test and improve the nucleation theories. Recent field observations and quantum chemical calculations have shown that organic amine compounds may be important for new particle formation, but the nucleation studies involving amines are entirely lacking. Our laboratory observations show that amines can enhance nucleation of sulfuric acid aerosols, very similarly to ammonia. The enhancement on nucleation rate due to base compounds is also related to the basicity of base compounds, indicating that acid-base reactions are important for formation of sub-3 nm particles and their subsequent growth. These results strongly imply that the effects of inorganic and organic base gases (ammonia and amines) on nucleation should be taken into account together to fully understand the widespread new particle formation events in the lower troposphere. Long-term atmospheric observations of aerosol sizes and precursors (sulfuric acid, ammonia and amines) made in Kent, Ohio (a relatively less polluted atmosphere) show that sulfuric acid is the most important aerosol nucleation precursor, consistent with laboratory observations. These results have an important implication on addressing how man-made sulfur dioxide can affect the aerosol number concentrations in the atmosphere. We also have developed a chemical ionization mass spectrometry (CIMS) technique to detect atmospheric amines with high sensitivity, low detection limit and fast time-response. Our CIMS can measure atmospherically-relevant amine compounds (containing one to six carbon atoms in a molecule) at pptv or tens pptv level, with a time response less than one minute. An undergraduate research module developed by the PI to measure solubility of organic compounds relevant to the atmosphere was used for undergraduate courses and research, in the PI’s university as well as other universities. The PI also taught chemistry to inner-city high school students enrolled in the Upward Bound Pre-College program, including a very high fraction of women and minorities. A high school student conducted research on atmospheric chemistry in the PI’s research group via the Post-Secondary Enrollment Option Pre-College program. The PI was involved in recruiting and mentoring a large number of undergraduate students majoring STEM field; a high fraction of these students were first-generation college students from low income families. Broad Impact: Despite the important effects of aerosols on global climate, atmospheric composition and human health, atmospheric aerosol formation mechanisms are poorly understood. Nucleation is a predominant source of new particles and thus is an important process that controls aerosol and cloud abundances. New particles may have significant indirect effects through their modification of cloud properties such as albedo, lifetime, and precipitation efficiency. Our observation data will thus help to reduce the uncertainties in the current aerosol nucleation theories and the uncertainties in the predictions of CCN concentrations in regional and global aerosol models. Under this NSF award support, postdoctoral, graduate and undergraduate students, including women and under-represented members in STEM, gained research experiences in atmospheric sciences and climate change.
