Investigation of seasonal variability of atmospheric columnar CO_2 over India in relation to environmental parameters using OCO-2 observation and vertical redistribution model

摘要

This work re-explores the seasonal change of atmospheric carbon dioxide (CO2) concentration, a subject of renewable interest over half a century, in both time and frequency domain and identifies the atmospheric surface pressure and the surface air temperature as key factors for the temporal variation. The annual variability of CO2 dry-air mole fraction derived from the National Aeronautics and Space Administration Jet Propulsion Laboratory (NASA-JPL) Orbiting Carbon Observatory-2 (OCO-2) database for the region bounded by 22 degrees N to 23 degrees N and 86 degrees E to 89 degrees E was found to increase in summer, to decrease in winter and to exhibit a tendency of increase at the end of the year consistently for the years 2016 and 2017 whereas the corresponding variations of solar-induced fluorescence, surface pressure and air temperature showed partial consistency with that. The trends of these findings were cross-checked with the long-time gross variations of CO2, Normalized Difference Vegetation Index, surface pressure and surface temperature for 25 urban regions within approximately 20 degrees N to 29 degrees N and 69 degrees E to 89 degrees E obtained from NASA-Giovanni database for a period of 2010 to 2017. The periodic variations of these parameters were pin-pointed by Fourier transform. Field measurements were carried out for ground level and column-averaged CO2 concentrations in parts per million (ppm) at the region around Kolkata city (22.55 degrees N, 88.35 degrees E). Based on the above findings, a simple atmospheric model is developed for vertical redistribution of CO2 molecules under changed temperature and pressure causing a changed atmospheric path for radiation absorption and an apparent change in the gas concentration at any specific altitude.