Cavity enhanced instruments for detection of hydrogen chloride and aerosol optical extinction

摘要

This thesis concerns the development of cavity enhanced instruments for atmospheric science studies. Hydrochloric acid (HCl) is an important reservoir species for active halogens which are thought to participate in cycles that deplete ozone. In order to understand these halogens and their effect on ozone depletion, a cavity ring-down spectroscopy (CRDS) based instrument was developed for ultra-sensitive HCl concentration measurements. The instrument has a (1 sigma) limit of detection of 10 pptv in 5 min and has high specificity to HCl. Aerosols are a fundamental contribution to Earth's radiation budget and represent one of the largest unconstrained unknowns in estimating climate change. The effect of aerosols on climate and air quality is closely tied to their spectral properties as well as particle chemical composition, size, and shape. Aerosol extinction coefficient (sum of light attenuation by scattering and absorption coefficients) is an important optical property for determining aerosol radiative forcing. A broadband cavity enhanced absorption spectroscopy (CEAS) laser-based instrument for measurement of aerosol extinction has been created with a minimum detectable extinction coefficient of 8x10 -8 cm-1 for 10-ms collection time. This thesis details the development and validation of these cavity enhanced spectroscopy based instruments.