Variabilities in CO2 and CO over an urban site in India: Inter-correlations and emissions characteristics.

Abstract:

CO₂, the most important greenhouse gas (GHG) in the atmosphere, plays a pivotal role in climate change. The long term increase in its atmospheric abundance after the Industrial Revolution is attributed to the emissions from anthropogenic activities, especially fossil fuel combustion. CO is a product of inefficient combustion and can be used as a surrogate tracer for identifying the anthropogenic and biospheric signal of CO₂ from the atmospheric observation. India is the second largest populous country in the world and share significant contribution in the emissions of greenhouse gases mainly CO₂. The budget of CO₂, estimated from top-down and bottom-up approaches, shows large uncertainties over the South Asian region than other continents. One of the major sources of these large uncertainties is the lack of spatial and temporal observations. An attempt has been made using a year-long period to study the variability of the levels of CO₂ and CO at an urban site Ahmedabad (23.03^oN, 72.58^oE, 55m AMSL), in the western India using a highly sensitive cavity ring down spectroscopy technique. The diurnal cycles of CO₂ and CO show distinct features to each other due to their diverse sources and sinks. Two significant peaks during the morning and evening hours have been observed in the diurnal cycle of CO₂ while in the case of CO evening peak is significantly higher than the morning peak. The afternoon levels of CO₂ are observed lower during monsoon, which shows the significant uptake of CO₂ from the biosphere during this season. The diurnal amplitude of CO₂ is found largest around 41 ppmv in autumn and lowest around 12 ppmv in monsoon. The seasonal cycles calculated from the afternoon average monthly CO₂ show the minimum levels during monsoon and maximum during spring. In case of CO minimum levels are observed in monsoon while maximum are observed in winter. The seasonal amplitude is observed around 15.02 ppmv and 0.27 ppmv for CO₂ and CO respectively. Further, the co-relation of CO_2, with CO is used to identify the dominant source types in different seasons. More details of the levels, the amplitude of diurnal as well as seasonal variations of CO₂ and CO in different seasons and their mutual interrelationship will be presented during the presentation.