The Characteristics Of Spatial-temporal Variations Of Atmospheric CO₂ And Its Influencing Factors In Shanghai, China

This paper has focused on spatial-temporal characteristics of atmospheric CO₂ by means of comprehensive sampling methods, both stationary and mobile, in mega city of Shanghai which is in the process of rapid urbanization. In the meantime, based on real-time data of hourly concentration of major air pollutants issued by state-controlled automatic monitoring station in Shanghai, correlation relationship between concentration of atmospheric CO₂ and major air pollutants were analyzed. The result of this paper may deepen the recognition for urban carbon cycle and provide more information about the influence of urbanization to carbon emission. Major results of this paper are as follows:（1） Temporal analysis has unveiled the variations of atmospheric CO₂ in Shanghai during the monitoring period. Concentrations of atmospheric CO₂ has ranged from 370-610 ppm （parts per million by volume） with an average of 441.9 ± 29.9 ppm. Nearly 80% of concentrations of atmospheric CO₂ were within 400-480 ppm. Atmospheric CO₂ exhibited significant diurnal variations with two peaks and one trough. The occurrence of high values was highly related to peak time with higher diurnal range happened in summer and winter. Additionally, seasonal variation analysis showed high atmospheric CO₂ concentration in autumn and winter and low values in spring and summer. Atmospheric CO₂ concentrations had negative correlation with both air temperature and wind speed （R=-0.56 and-0.51, p<0.01）. Wind direction would significantly affect the redistribution of near-surface atmospheric CO₂ concentration. Atmospheric CO₂ concentrations were elevated when sampling point was at downwind of emission site.（2） Both stationary and mobile sampling campaign indicated significant spatial heterogeneity of near-surface atmospheric CO₂ in Shanghai. Near-surface atmospheric CO₂ concentration had a significant negative relationship with distance from urban core （DUC） with a well-shaped carbon dioxide dome in Shanghai. Near-surface atmospheric CO₂ concentrations were closely related to urbanization levels and land use types.（3） This paper focused on quantitative analysis on the relationship between atmospheric CO₂ concentrations and land use types based on biophysical components of underlying surface derived from （Vegetation-Impervious Surface-Soil, V-I-S） model. Result showed that correlation coefficients between biophysical components （ISA and Veg） and CO₂ concentrations reached maximum when buffer distances were 2 km and 5 km for stationary （R=0.51 and -0.50 for ISA and Veg） and mobile （R=0.67 and -0.63 for ISA and Veg） sampling campaign, respectively. Multiple regression model was constructed with ISA and Veg as independent variables and CO₂ concentrations as dependent variable: CO₂= 0.99ISA-0.18Veg+378.18 （R2= 0.44,p<0.01）（4） Characteristic of diurnal variation of major pollutants could be classified into two groups:"Two peaks and troughs" and "Single peak" type. PM2.5, PM10, CO and NO2 could be grouped into "Two peaks and troughs" type while O3 and SO2 could be grouped into "Single peak" type. PM2.5, PM10, CO, NO2 and SO2 were significantly positively correlated with atmospheric CO₂ （R=0.586,0.539,0.515,0.620 and 0.517） affected mainly by peaks of working hours while O3 were negatively correlated with atmospheric CO₂ （R=-0.496） affected mainly by photochemical reactions.