Abstract
We report on the design, development, and field deployment of a 10-mW, 4320-nm distributed-feedback quantum cascade laser-based tunable diode laser spectroscopy (TDLS) system in India for in situ measurement of atmospheric CO2. The portable system was deployed at Mount Abu (24.5926° N, 72.7156° E), a hill station in western India, to carry out week-long measurements of background atmospheric CO2 using direct detection. The mean mole fraction was estimated to be 396 ± 8 ppm. The system was then deployed in Gandhinagar (23.2156° N, 72.6369° E), the capital of the state of Gujarat, to make foreground measurements over the next week. The mean mole fraction at this location was 503 ± 27 ppm. The difference between the background levels in Mount Abu and foreground levels in Gandhinagar is evident. The detection limit of the system, as measured from an Allan variance analysis, was determined to be 260 ppb for an integration time of 58 s and a path length of 20 cm, which is sufficient for such measurements. Another compact and light-weight TDLS system was also deployed for water vapor measurement. It consisted of a 1392.54-nm distributed feedback laser driven by custom electronics and a digital signal processor to carry out waveform generation, data acquisition, and postprocessing tasks.
Highlights
Accurate in situ measurement of greenhouse gases (GHGs) is a key requirement in modern climate science research
In 1993, an air sampling station was established at Cape Rama through the collaborative efforts of the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO), Physical Research Laboratory (PRL), Ahmedabad, and National Institute of Oceanography, Goa
This paper reports the first midinfrared tunable diode laser spectroscopy (TDLS)-based comparison of foreground and background atmospheric CO2 levels in India
Summary
Accurate in situ measurement of greenhouse gases (GHGs) is a key requirement in modern climate science research. Data are not available over long time intervals and over large geographical regions This makes it difficult to understand the variations of carbon dioxide over the Indian subcontinent.[15] there is a pressing need to develop robust portable sensors for continuous monitoring of GHGs over India. We report the design and field deployment of a compact, rugged, and portable midinfrared tunable diode laser spectroscopy (TDLS) system in India for in situ high-sensitivity and continuous measurement of atmospheric CO2. This is the first instance of such a system being deployed anywhere in India. This study aims to demonstrate that robust TDLS systems can be built to fill the measurement gaps that currently exist
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