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Aerosol Microphysics Research at ASRC

Researchers:  Fangqun Yu

In recent years, increasing attention has been focused on the influence of atmospheric aerosols on climate and atmospheric chemistry as well as the adverse health effects associated with fine particles. The effects of aerosols on health, chemistry and climate are sensitive to particle size and concentration, which are influenced significantly by nucleation processes. However, the fundamental mechanism of new particle formation remains poorly understood despite intensive research over the past several decades. A clear understanding of the formation mechanisms and processes controlling the properties of atmospheric aerosols is critical in assessing of the potential climatic/environmental/health effects associated with particle pollution, and in finding solutions to these problems.

Our primary research interests are theoretical studies and numerical simulations of processes controlling the formation, evolution, and properties of atmospheric aerosols. We seek to achieve a better understanding of the key mechanisms determining the variability of condensation nuclei (CN) and cloud condensation (CCN) abundance in the troposphere. We have developed an advanced particle microphysics (APM) model which is capable to simulate the microphysics of a multi-type, size-dispersed, composition-resolved aerosol system. The APM model (APMM) is built to be flexible, modular, and efficient, and can be easily reconfigured to study various aerosol-related problems. One of the unique features of the APMM is the inclusion of size-resolved electrical charge effects. The APM model has been successfully applied to applied to analyze a number of specific, and unusual, aerosol data sets.

We have proposed a new formation mechanism of atmospheric aerosols - ion-mediated nucleation (IMN). The charged molecular clusters, condensing around natural air ions, can grow significantly faster than corresponding neutral clusters, and thus can preferentially achieve stable, observable sizes. The APM model incorporates the complex charged and neutral processes from molecular size to nanometer scale that define IMN. The IMN theory can physically explain the enhanced growth rate of sub-nanometer clusters, and seems to account consistently for ultrafine aerosol formation in jet plumes, in clean continental air and in marine boundary layer, as well as for the observed diurnal variation in the atmospheric mobility spectrum. We are analyzing other measurements related to particle nucleation (in cloud outflows, in vehicle exhaust, etc.).

The IMN theory and numerical simulations provide theoretical guidance for a proposed European experiment called CLOUD at CERN, the European particle physics laboratory in Geneva. The CLOUD project is intended to test the cosmic ray-aerosol-cloud hypothesis and involves prominent scientists from many European countries. Dr. Yu has been invited to join the CLOUD investigation team.

The long-term research objective is to develop an efficient and practical aerosol microphysics module using the APM model as a basis, and couple the module to chemical transfer models (both regional and global scale) to study various aerosol related problems. The aerosol module will resolve the size and composition of particles for a range of types (including internal and external mixtures), and will contain empirical formulas (developed through detailed studies) to simplify microphysics processes for efficiency.