Laboratory studies of organic haze aerosols in simulated planetary atmospheres.

摘要

The photolysis of methane (CH4) is known to produce organic haze particles in the atmospheres of several planetary bodies, including Saturn's moon Titan. Part of the interest in Titan is as a model for early Earth, which may have contained significant levels of atmospheric CH 4 prior to the rise in oxygen (O2). However, it is unclear whether a haze layer would form on early Earth since carbon dioxide (CO 2) would also have been present. This thesis examines organic aerosol products formed under simulated planetary conditions in order to explore the mechanisms for haze formation on Titan and the possibility of a haze layer on the early Earth.; In the laboratory, the chemical and physical properties of planetary haze aerosols were measured using a flowing reactor cell coupled to in-situ analysis. An Aerosol Mass Spectrometer was the primary instrument, used in combination with electric discharge and ultraviolet (UV) energy sources.; For Titan simulations, aerosols were produced from various mixtures of CH4 in nitrogen (N2). The chemical composition of aerosols was found to contain several hydrocarbon and aromatic species, with some variation between energy sources. The UV experiments showed that the amount of aerosol mass produced in the laboratory could be used to accurately estimate the observed haze in Titan's atmosphere.; The production of organic haze in simulated early Earth atmospheres was studied from CH4/CO2 ratios of 10 to 0.2. Experiments showed that the introduction of CO2 affected the level of aerosol mass production and altered the chemical nature of the haze aerosols. With the addition of CO2, the particle composition differed from the Titan haze analogs, containing larger quantities of oxidized organic species such as carboxylic acids. Studies with the UV lamp showed that particle mass production reached a maximum rate at a C/O ratio of unity. Results from the UV experiments were used to estimate the aerosol flux in the early Earth atmosphere to be approximately 1014 g year-1. These findings suggest that a haze layer on the early Earth may have been probable under several atmospheric conditions, and could have been a plentiful source of organics to the surface.