Development of Optical Spectroscopic Instruments and Application to Field Measurements of Marine Trace Gases

摘要

Halogens (X = Cl, Br, I) and organic carbon are relevant to the oxidative capacity of the atmosphere, are linked to atmospheric sulfur and nitrogen cycles, modify aerosols, and oxidize atmospheric mercury. The abundance of halogen radical species in the atmosphere is very low, but even concentrations of parts per trillion (1 ppt = 10-12 volume mixing ratio) or parts per quadrillion (1 ppq = 10-15 volume mixing ratio) are relevant for the aforementioned processes.Halogen radicals can be traced through measurements of halogen oxides (XO, where X = Cl, Br, I), that are ~1-10 times more abundant. However, measurements of halogen oxides are sparse, partly due to the lack of analytical techniques that enable their routine detection. In Chapters II-IV, I describe the development of a research grade Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument to measure bromine monoxide (BrO) and iodine monoxide (IO) routinely in the troposphere. I present autonomous measurements of BrO and IO in Pensacola, Florida that maximize sensitivity towards the detection of BrO in the free troposphere (altitudes u3e2km) from ground. The measurements are then coupled to a box-model to assess their impact on the oxidation of mercury in the atmosphere. Chapter V describes the Fast Light-Emitting- Diode Cavity-Enhanced DOAS (Fast LED-CE-DOAS) instrument and first measurements of glyoxal diurnal cycles and Eddy Covariance (EC) fluxes of glyoxal in the marine atmosphere. Glyoxal is the smallest α-dicarbonyl and a useful tracer molecule for fast photochemistry of hydrocarbons over oceans. The unique physical and chemical properties of glyoxal pose challenges in explaining this soluble gas over the remote ocean, and recent measurements over the open ocean currently remain unexplained by models. Results from a first cruise deployment over the tropical Pacific Ocean (TORERO field campaign) are presented.