Three-dimensional spatiotemporal variability of CO in suburban and urban areas of Shaoxing City in the Yangtze River Delta, China.

Metropolitan areas are the most anthropogenically active places but there is a lack of knowledge in carbon dioxide (CO) spatial distribution in suburban and urban areas. In this study, the CO three-dimensional distributions were obtained from 92 times vertical unmanned aerial vehicle (UAV) flight observations in Shaoxing suburbs and 90 times ground mobile observations in Shaoxing urban areas from Nov. 2021 to Nov. 2022. The vertical distribution showed that CO concentrations gradually decreased from 450 to 420 ppm with altitude from 0 to 500 m. CO vertical profile concentrations can be influenced by transport from multiple regions. Based on the vertical observation data combining a potential source contribution function (PSCF) model, Shaoxing suburban CO were to be derived from urban areas in spring and autumn, while in winter and autumn were mainly from the long-transports from neighboring cities. Further the CO concentrations of urban horizontal distribution were observed in the range of 460-510 ppm through the mobile campaigns. Urban CO were partly emitted from traffic exhausts and residential combustion. Overall, CO concentrations were observed to be lower in spring and summer due to the CO uptake by plant photosynthesis. This uptake was initially quantified and accounted for 4.2 % of total CO in suburbs and 3.3 % in urban areas by calculating the decrease in CO concentration from peak to trough in the daytime. Compared with the CO observed in the Lin'an background station, the maximum regional CO enhancement in Shaoxing urban areas reached to 8.9 % while the maximum in suburbs only 4.4 %. The contribution differences between urban and suburban areas to regional CO were relatively constant at 1.6 % in four seasons may be mainly ascribed to the contribution of long-range CO transport to the suburbs.