A low power automated MAX-DOAS instrument for the Arctic and other remote unmanned locations

Abstract

Multiple Axis Differential Optical Absorption Spectrometer (MAX-DOAS) systems are inherently very simple instruments, which have been shown to provide extremely useful information about a wide variety of environmental parameters. In order to exploit the potential of the technique we have developed a new field-deployable, passive MAX-DOAS system that is automated and uses little power (<3 W). This new instrument utilizes a fully enclosed scan head that protects all moving parts and optics from harsh environments. Instrument diagnostics, such as tilt monitoring and frost accumulation detection and removal, are integrated into the main data acquisition program, which then acts to remedy problems that were discovered. This full automation and data quality checking make this instrument ideal for long-term deployment at remote, unmanned locations around the world, such as in polar regions or in the monitoring of trace gas emissions from volcanoes. This instrument was recently integrated into an ice-tethered autonomous buoy and tested in Elson Lagoon, near Barrow, Alaska to monitor halogen chemistry in the Arctic. During this investigation, differential slant column densities (dSCDs) of BrO up to 6×1014 molecules/cm2 were observed. Typical spectral fit residual RMS optical densities were less than 6×10-4 for solar zenith angles (SZA) <80° and a 6-min integration time. Here we describe the design concepts and performance of this new MAX-DOAS instrument through detailed analyses of spectral quality, power usage, possible instrument response biases, and typical instrument operations.