Spatial variation of near-surface CO₂ concentration during spring in Shanghai

Urban area plays an important role in global carbon cycle, yet few efforts have been made to investigate CO₂ concentration and its spatial heterogeneity in cities. Using Shanghai, the commercial and financial center of mainland China, as a case study, this paper explored the spatial pattern and determinants of near-surface urban CO₂concentration during spring. A total number of 173 sample points were collected covering the whole urban area, to examine the atmospheric CO₂ concentration across various land use types (transportation, commercial, agricultural, recreational, institutional, residential and industrial land use) and urbanization gradients (heavy, moderately heavy, medium, moderately low, and low urbanization). CO₂ concentrations were measured at a height of 2 m above the ground during 9:00–11:00 am in April and May 2014. The results indicated that CO₂ concentration for the region was 409.4 ± 20.8 parts per million (ppm), showing significant spatial heterogeneity. The daytime ambient CO₂ concentration varied across land use types (p < 0.05), with the highest and lowest value appeared in transportation area (420.5 ± 33.3 ppm) and agricultural land (398.9 ± 16.2 ppm). Across the urban gradients of Shanghai, a significant decrease of CO₂ concentration was observed as the distance from urban core increased. With the influence of both high residential density and activities in production, the highest CO₂ concentration occurred in moderate urbanization area (423.9 ± 29.3 ppm), rather than the high urbanization area (417.2 ± 17.5 ppm). Further analysis indicated that the percent of impervious surface cover (ISA) was an important indicator to describe near surface CO₂ concentration with a positive correlation, and the percent of vegetation coverage (Veg) had lower explanatory power with a negative correlation. When buffer distance of spatial scale was 2000 m, atmospheric CO₂ concentration showed the highest correlation with impervious surface and vegetation coverage.