A study of the formation and evolution of aerosols and contrails in aircraft wakes: Development, validation and application of an advanced particle microphysics (APM) model.

摘要

The aerosols generated by current and future fleets of subsonic and supersonic aircraft may affect stratosphere ozone abundances by enhancing the particulate surface area on which heterogeneous chemical reactions can occur, and may affect global climate by modifying high-level clouds. A reliable assessment of aviation impacts requires a thorough understanding of the mechanisms that control the production and physical properties of the emitted particles.;This dissertation discusses the development of an advanced particle microphysics (APM) model, and the application of this model to investigate the formation mechanisms and physical properties of the aviation-generated aerosols. In the model, the composition and size distributions of various categories of particles (electrically charged and uncharged, volatile and nonvolatile, and liquid and solid) are tracked through the different phases of plume evolution, including the condensation and evaporation of contrails when ambient conditions favor ice formation. The APM model is modularized and highly efficient, and may be applied to study a variety of aerosol-related problems. Here, the model is applied to analyze in-situ plume particle observations obtained in several field campaigns.;The simulations---constrained by measurements---reveal that the largest volatile particles---those most likely to contribute to the background abundance of condensation nuclei---are dominated by "ion-mode" aerosols, which are formed on the chemiions emitted by the aircraft engines. The population of ion-mode aerosols is controlled by the abundance of chemiions which is determined by combustion chemistry and is relatively invariant. The theory of chemiion effects on aircraft plume microphysics is developed here, and the first quantitative calculations of chemiion-influenced plume aerosols are presented. In this work, a molecular kinetic model is used for the first time to interpret in-situ aircraft particle measurements, showing that the commonly-applied "classical model" may be invalid for simulating plume microphysics. The results indicate that reductions in fuel sulfur content, while not likely to be effective in reducing the total number of volatile particles formed in aircraft exhaust, will reduce the size of the evolving ion-mode particles, reducing their atmospheric lifetime. Simulations also indicate that contrail formation can be critical in generating exhaust particles that later act as cloud condensation nuclei (CCN) or ice nuclei (IN). The number of available CCN/IN determines the high-altitude cloud radiative properties of importance to climate studies. Further, it is shown that organic species emitted by aircraft engines may dominate the mass of volatile particles with low-sulfur-content fuels.