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Multidimensional Characterization of Individual Aerosol Particles with Special Focus on Secondary Organic Aerosol

Small, ultrafine and fine aerosol particles are ubiquitous in natural and human-made environments, playing an important role in many areas that have direct impact on our lives. The behavior and impacts of aerosol particles, including effect of atmospheric aerosols on air quality, visibility, human health, and climate, depend on a number of their physical and chemical properties, many of which are strongly coupled. Particle number concentration, size, internal composition, density, phase, shape, morphology, mass, hygroscopicity, activity as cloud condensation and ice nuclei, optical properties, and other attributes - all play a role. Traditional particle characterization approaches rely on a number of independent measurements that average over a heterogeneous mixture of particles of different properties and later attempt to draw correlations between all observables. As a result, major differences between individual particles are often overlooked. It follows that simultaneous characterization of all the relevant attributes of individual particles is essential to achieve fundamental understanding of the properties, evolution, and impacts of small particles.

Over the years we have been developing novel approaches to measure simultaneously, in-situ and in real-time, a large number of attributes for individual particles, using our single particle mass spectrometers, SPLAT II and miniSPLAT, in combination with other instruments. This multidimensional single particle characterization yields comprehensive, quantitative analysis of individual particles with ultrahigh sensitivity, sub-nanometer precision and accuracy, and with high temporal resolution.

I will demonstrate the utility of this approach to characterize individual particles that contain secondary organic aerosol (SOA) material. I will show how the results of these studies, in which we characterized size, composition, morphology, density, shape, viscosity, chemical diffusivity, evaporation kinetics, and rates of heterogeneous reactions of size-selected SOA particles, provide unique insights into the processes that drive SOA formation, properties, and atmospheric evolution.