[Near surface atmospheric CO2 variations in autumn at suburban Xiamen, China].

Near surface concentrations of carbon dioxide (CO2) were measured at the super station of atmospheric monitoring located at the suburban area of Xiamen in the fall of 2011. The results were analyzed together with the meteorological data and concentrations of other gaseous pollutants to study the diurnal variations of near-surface atmospheric CO2 concentration and the relationships of CO, with wind speed and gaseous pollutants. The diurnal variation of CO2 concentrations showed a single-peak pattern with the highest value (408.54 micromol x mol(-1)) observed in dawn when the atmosphere was stable and the lowest value (379.14 micromol x mol(-1)) was recorded in late afternoon following several hours of relatively unstable condition. The average CO, concentration at night (400.87 +/- 4.05) micromol.mol(-1) was higher than that of daytime (388.8 +/- 9.40) micromol c mol(-1). Overall, the COz concentrations ranged from 375.74 micromol.mol(-1) to 418.18 micromol x mol(-1). CO2 and wind speed showed opposite trends. At night the CO2 concentration (400.72 +/- 2.12) micromol x mol(-1) was stable with wind speed of 1.0-1.5 m x s(-1). During daytime, the CO2 concentrations 379.14-394.83 micromol x mol(-1) were more variable with wind speed of 2.0-2.5 m x s(-1). The background CO2 concentration of this site was estimated to be 386.84 micromol x mol(-1) using an exponential function model. Northeast wind was dominant at this site. The correlation coefficient between the wind speed and the CO2 concentrations (r = -0.67, P < 0.01) was higher for wind direction of NE than other directions (r = -0.41, P < 0.01). The source contributions were different for different wind directions. Moreover, the CO2 concentration had a significant negative correlation with temperature and irradiation, and had a significant positive correlation with humidity. CO2 had a higher correlation with primary air pollutants CO and NO (r = 0.469/0.436, P < 0.01) than SO2 (r = 0.126, P < 0.01), indicating that the source of CO2 emission in this area was motor vehicle emission in part, with little contribution from coal combustion.