Observations of trace gases in the earth's lower atmosphere: Instrumentation and platform

The earth's atmosphere is a complex mixture of many gases and their observations are incorporated in chemistry-climate models. Atmospheric observations have been the backbone of recent progress in atmospheric science, particularly about our understanding of the sun-atmosphere interaction causing chemical and radiative forcing linked to the environment and climate change. In terms of technology, there has been significant progress in both in situ and remote sensing measurements of several variables in the lower atmosphere. Among them, trace gases play an important role in climate change and several environmental problems. The recent progress in both in situ and remote sensing-based instrumentation has enabled researchers to study various atmospheric processes in great detail. For example, gas chromatography-based instrumentation provides detection from simple to complex species present in the atmosphere at very low concentrations. The laser-based spectroscopic instruments are emerging tools for fast response measurements of trace gases, which are important to understand rather short-term processes. The proton transfer reaction-mass spectrometry is regarded as one of the best technologies for the detection of numerous but specific types of trace gases, namely volatile organic compounds. However, there are advantages and disadvantages of any instrument in terms of quality of data, comprehensiveness and cost. In this article, we discuss the recent progress in instrumentation used for the measurement of trace gases in the lower atmosphere utilizing space, aircraft and satellitebased platforms as well as some laboratory techniques. We also briefly highlight the progress made during the past couple of decades, present status and future scenarios of trace gas measurements in the South Asia region.