DIURNAL AND SEASONAL VARIATION OF MEASURED ATMOSPHERIC CO_2 AT DEHRADUN DURING 2009

摘要

Atmospheric carbon dioxide (CO_2) is the major greenhouse gas. We analysed the diurnal trend and seasonal variations of atmospheric Carbon Dioxide (CO2 ) measured at Dehradun during 2009. The measurements are taken from the Vaisala CO_2 probe installed at the top of the IIRS building. A distinct diurnal cycle with seasonal variations is present in these measurements. Diurnal cycle exhibits a half sinusoidal variation with decreasing phase during sunrise to afternoon and increasing phase during afternoon to sunset. CO_2 mostly remains constant with higher values during the night. The largest negative anomaly with respect to the annual mean varies betwe en +/-20 ppmv with positive anomaly during the night time and negative anomaly during the day time. The cause of such variation could be attributed to the local ecosystem activity. During the day time the sinking of CO_2 through the photosynthesis dominates its release through autotrophic and heterotrophic respiration. On the other hand, photosynthesis has been ceased during the night time and respiration only controls the night variation of CO_2. There exists significant change on the diurnal cycle of CO_2 in different seasons during the year. The maximum rapid decrease in CO_2 concentration in early morning hours is due to photosynthetic activity during the monsoon periods (maximum in August -8ppm). During monsoon period rapid night time increase of CO_2 is observed due to the enhancement of respiration. An inverse relationship exist between model simulated net ecosystem productivity and CO_2 deviations on monthly basis. This diurnal and seasonal variations in situ CO_2 are in confirmation with model simulated results.