Measurement of Vertical Profiles of CO_2 In The Atmospheric Boundary Layer At A Suburban Site In Summer

摘要

Knowledge of vertical CO_2 distribution is required for developing 3-D CO_2 transport models and calibration/validation of satellite-borne measurements with ground based remote sensing instruments. In this study, vertical profiles of CO_2 concentration within 0-1000 m were measured using a tethered balloon at a suburban site in Xiamen which is undergoing fast urbanization. The characteristics of CO_2 vertical distribution and the impact from meteorological and anthropogenic factors were investigated using the extended dataset of vertical profiles obtained under both stable and convective boundary-layer conditions during the field campaign. Most of the profiles demonstrated a declining trend of CO_2 concentration with increasing altitude. However, opposite patterns were also observed for some cases that the CO_2 concentration started to increase with altitude above certain heights, where the top of mixing height or inversion layer could be reached according to simultaneous relative humidity and temperature measurements. The correlation of high altitudes and ground level CO_2 concentrations decreased with altitude and show high correlation in the first 300 m with R = 0.783 of 100 m, R = 0.524 of 200 m, R = 0.401 of 300 m (P＜0.01). When comparing the vertical profiles obtained at different times during a day, it was found that CO_2 concentration exhibited more obvious diurnal pattern at surface level than at high altitude because of the variation of sources and sinks of CO_2 at ground level. The influence of ground level CO_2 diurnal variation was restricted within the lower 350 m of the atmosphere. The general vertical profiles of CO_2 were fitted to obtain an empirical equation for estimating CO_2 vertical concentration in the lower atmosphere (0-1000m): y = -75.04+1.17e~(-x/28.01), R~2 = 0.59.