Observation And Analysis On Distribution Of CO₂Concentration In Nanjing

Greenhouse gas emission is one of the important causes of global climate change, it’s environmental and ecological effects has been caused for the world wide concern. City has high degree of industrialization, large population, clogged roads, high density of buildings and few green spaces; although the city area is small but the energy consumption is high. City has a significant contribution to the global carbon emissions; therefore, the study of carbon emission in city plays an important role in the global energy conservation and emission reduction. From2013to2014, multi-point continuous CO2concentration observation in City canopy was carried out through the establishment of city scale CO2concentration observation network in Nanjing. We analyzed the distribution and forming reasons of CO2concentration within the city canopy in summer and winter in Nanjing. The main conclusions are as follows:(1) the temperature range of self-made incubator can be controlled from1to45℃with a precision of±0.1℃. Calibration of CO2/H2O concentration with the frequency of once a day can make the observational error of CO2/H2O concentration within2μmol·mol-1/0.02%and this had been validated in the urban CO2concentration observation.(2) The average CO2concentration in Nanjing urban area is421.5μmol·mol-1in summer, and450.6μmol·mol-1in winter; the average CO2concentration in Nanjing suburbs is362.4μmol·mol-1in summer, and362.4μmol·mol-1in winter. The average CO2concentration is higher in urban area than in suburb, higher in winter than in summer.(3) Amplitude of changes of CO2concentration in Nanjing urban area is39.2μmol·mol-1in summer and24.8μmol·mol-1in winter; Amplitude of changes of CO2concentration in Nanjing suburbs is54.9μmol·mol-1in summer and42.1μmol·mol-1in winter. Amplitude of changes of CO2concentration is larger in summer than in winter, higher in Urban area than in suburb. (4) Diurnal variation of CO2concentration in Nanjing urban area in summer showed obvious "unimodal" trend, but" bimodal " trend in winter. The peak of CO2concentration occurred earlier in the winter than in the summer. Spatial distribution of CO2concentration of the city also has a seasonal variation, in the summer, CO2concentration from high to low as commercial areas, residential areas and city parks, opposite in winter.(5) The CO2concentration and wind speed show a significant anti correlation relationship. The wind speed increased when the CO2concentration decreased, the wind speed decreased when the CO2concentration increased. Lower CO2concentration value distributed in the in the large wind speed area, and high CO2concentration values are distributed in smaller wind speed area, there was no significant correlation with the wind.(6) CO2concentration in urban area is mainly affected by the atmospheric stratification stability and the source structure of underlying surface. The time variation of CO2concentration is mainly affected by the diurnal and seasonal variation of atmosphere stratification stability; and spatial variation of CO2concentration mainly depends on the variation of underlying surface source structure, such as transport carbon source, city residents living carbon source and urban green space carbon source.