Temporal and Spatial Variations of Atmospheric CO2 in Nanjing, China

Observational study on urban CO2 concentration is important for quantify its sources and sinks in urban landscapes. Globally, much more CO2 is emitted from anthropogenic sources in urban area with comparison to suburbs and the natural landscapes. In this study, street-level and spatial patterns of CO2 concentration were measured in the city of Nanjing, China. Nanjing is the second largest city in East China, with rapid economic development and dense population of 5.11 million people. Five non-dispersive infrared (NDIR) CO2/H2O gas analyzers (model LI-840A, LI-COR, Inc., Lincoln, NE, USA) were used to measure atmospheric CO2 concentration. To ensure stable performance, the analyzers were put in home-made temperature-controlled enclosureses with constant temperature of 43oC (± 0.3oC). In addition, a portable CO2/CH4/H2O analyzer based on Off-axis Integrated Cavity Output Spectroscopy (model 915-0011, Los Gatos Research, Mountain View, CA, USA) was used to make comparison. In this paper, we report the results of the following experiments:

(1) Spatial transects: To investigate the effect of traffic volume on the CO2 emission, we used the NDIR analyzers to measure the CO2 concentration along 4 main streets on three working and two weekend days in the summer (June 2013) and winter (January 2014).

(2) Stationary measurements at street-level: To study the effect of land cover on the atmospheric CO2 concentration, we conducted street-level CO2 measurements at five locations representative of five land use types of the city (old residential, new residential, park, commercial and university campus) in the summer (July and August 2013) and winter (January 2014).

(3) Station measurements on tall buildings: These measurements are being made on the roof of 5 tall buildings (20-30 m tall) located in the north, east, south, west and middle of the Nanjing city. The data will be used with a box model to determine the spatial and temporal variations of the urban surface CO2 source strength.