Atmospheric aerosols, small particles suspended in the atmosphere, have extensive impacts on climate and human health. In the atmosphere, aerosols alter the Earth's radiative balance by directly scattering and absorbing solar radiation and acting as the nuclei of cloud droplets and ice crystals, which change cloud lifetime, brightness, and precipitation patterns. Inhaled atmospheric aerosols have been linked to both acute (asthma, myocardial infarction (heart attack), arrhythmia, and stroke) and chronic (decreased life expectancy, increased risk for cardiovascular morbidity, and respiratory disease) effects. The recent expanded production and use of engineered nanoparticle represents another system with complicated environmental chemistry impacts. However, despite their importance, large uncertainties exist regarding the impacts aerosols and engineered nanoparticles on climate and health effects due poor understanding of their properties at a fundamental molecular level.
Our research focuses on improving our understanding of aerosol and nanoparticle physicochemical properties, their continuing chemical evolution in the atmosphere, and their subsequent deposition/inhalation at the earth's surface on global to neighborhood scales. Given that particles can have atmospheric lifetimes of days to weeks, an aerosol can undergo heterogeneous chemical reactions, internal phase separations, photochemical reactions, surface chemical reactions, and the partitioning of species between the gas and particle phases in the environment. To deconvolute the processes in this complex system requires the use of a wide of array of analytical/physical measurement techniques, including:
Single Particle Mass Spectrometry - We will utilize a single particle mass spectrometer that measures, in real-time, the size and chemistry of individual particles through light scattering and time-of-flight mass spectrometry of positive and negative ions generated through laser desorption/ionization.
Raman Microspectroscopy - Recent advances in the capabilities of Raman microspectroscopy instrumentation allow for the detailed analysis of vibrational spectra at the single particle level for atmospherically relevant sizes. The functional group information obtained with Raman complements the molecular and elemental information provided by the single particle mass spectrometer, along with providing morphological information at ambient pressure.
Transmission Electron Microscopy/Scanning Electron Microscopy - Electron microscopy allows for detailed particle imaging, along with obtaining elemental information from energy dispersive X-ray (EDX) analysis and chemical speciation from electron energy loss spectroscopy (EELS).
By integrating field measurements, laboratory measurements on field samples, and laboratory measurements on proxies, this integrated approach is allowing us to tackle important atmospheric processes ranging from: the complex chemistry on metal-containing particles in ship plumes, the impact of long range transported of urban particulate matter and mineral dust on remote locations, the different aerosol sources impacting urban areas on the neighborhood scale, and the impact of atmospheric processing on engineered nanoparticles in the atmosphere. This interdisciplinary research involves collaborating with researchers in many fields, including atmospheric science, industrial hygiene, civil and environmental engineering, epidemiology, and oceanography. The broad aim of our group is to provide chemical information that can be used to reduce aerosol uncertainties by improving representation in climate models and increasing understanding of the chemistry behind negative health effects.
Ault, A. P.; Zhou, D.; Ebben, C. J.; Tauber, M. J.; Geiger, F. M.; Prather, K. A.; Grassian, V. H., Raman Microspectroscopy and Vibrational Sum Frequency Generation Spectroscopy as Probes of the Bulk and Surface Compositions of Size-Resolved Sea Spray Aerosol Particles. Physical Chemistry Chemical Physics (2013), In Press, DOI: 10.1039/C3CP43899F.
Ault, A. P.; Peters, T. M.; Sawvel, E. J.; Casuccio, G. S.; Willis, R. D.; Grassian, V. H. Single Particle SEM-EDX Analysis of Iron-Containing Coarse Particulate Matter in an Urban Environment: Sources and Distribution of Iron within Cleveland, Ohio. Environmental Science and Technology (2012), 46(8), 4331-4339.
Ault, A. P. and Pomeroy, R. Quantitatively Investigating Biodiesel Fuel Using Infrared Spectroscopy: An Instrumental Analysis Experiment for Undergraduate Chemistry Students. Journal of Chemical Education (2012), 89(2), 243-247.
Ault, A. P.; Williams, C. R.; White, A. B.; Neiman, P. J.; Creamean, J. M.; Gaston, C. J.; Ralph, F. M.; Prather, K. A. Potential Changes to California Orographic Precipitation due to Transported Asian Dust. Journal of Geophysical Research - Atmospheres (2011), 116, D16205, doi:10.1029/2010JD015351.
Ault, A. P.; Gaston, C. J.; Wang, Y.; Dominguez, G.; Thiemens, M. H.; Prather, K. A. Characterization of the Single Particle Mixing State of Individual Ship Plume Events measured at the Ports of Los Angeles and Long Beach. Environmental Science and Technology (2010), 44(6), 1954-1961.
Ault, A. P.; Moore, M. J.; Furutani, H.; Prather, K. A. Impact of Emissions from the Los Angeles Port Region on San Diego Air Quality during Regional Transport Events. Environmental Science and Technology (2009), 43(10), 3500?3506.