Abstract
This article describes the prototype of a new MAX-DOAS (multi-axis differential optical absorption spectroscopy) system built at “Dunarea de Jos” University of Galati (UGAL), Romania, and the first results of its use to observe NO2 content over Galati city (45.42° N, 28.04° E). The new equipment is a ground-based MAX-DOAS system capable of measuring the spatial distribution of DSCD (differential slant column densities) of several trace gases using horizontal and vertical observations. The new optic system, named UGAL-2-DOAS, is an in-house, low-cost, solution in comparison to the existing market of the MAX-DOAS systems. This paper describes the technical design and capabilities of the new MAX-DOAS instrument. The UGAL-2D-DOAS system was tested in April and June 2017 in Galati city. Measurements over three days were selected for the present manuscript. Full azimuthal (0–360°), local celestial meridian observations and other elevation angle sequence measurements (e.g., E–W) were performed. We found that the new MAX-DOAS system is able to detect diurnal variation and the local source emissions of NO2 from the urban environment. Also, we present concomitant zenith-sky car-DOAS observations measurements around the location of the new MAX-DOAS instrument. Comparing the horizontal scanning sequence of the new developed instrument with the mobile DOAS observations, we found that both systems can indicate and detect the same NO2 sources.
Highlights
The differential optical absorption spectroscopy (DOAS) technique is a remote-sensing detection method that uses scattered light to retrieve information about the abundance of several trace gases in the lower layers of the atmosphere
The first experiment using the University of Galati (UGAL)-2D-DOAS system was conducted under the horizontal scanning mode (HSM)
We described here a low-cost MAX-DOAS system, developed at the “Dunarea de Jos” University of Galati, Romania, named UGAL-2D-DOAS
Summary
The differential optical absorption spectroscopy (DOAS) technique is a remote-sensing detection method that uses scattered light to retrieve information about the abundance of several trace gases in the lower layers of the atmosphere. This measurement technique uses the transmitted ultraviolet–visible (UV–Vis) signal in active (artificial light source) and passive (natural sources e.g., Sun) applications. The first use of passive UV–Vis spectroscopy for measurements of atmospheric O3 using a single spectral domain in zenith observations was performed by Dobson and Harrison in 1925 [1,2]. DOAS experiments used zenith-sky geometry for retrieving information about trace gases and aerosols in the troposphere and stratosphere [3]. The combination between a large range of horizontal and vertical viewing directions led to a new DOAS technique, called MAX-DOAS (multi-axis differential optical absorption spectroscopy) [4,11]
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