[Spatial and temporal variations of near surface atmospheric CO2 with mobile measurements in fall and spring in Xiamen, China].

The study on the spatial distribution of near surface air pollutants carbon dioxide (CO2) and particulate matters (PM) is essential for understanding the pollution characteristics with mobile measurements. Near surface concentrations of CO2, PM and meteorological parameters were measured in Xiamen city, China along the route passing through different functional areas using the mobile laboratory during different time periods of the day [09:00- 12: 00, 13 :00- 16 : 00, 22 : 00-01 : 00 (local time) ] in spring (April) and fall (November), 2013. Carbon dioxide, PM and meteorological parameters data were analyzed for the spatial distribution of CO2 in different functional areas and the relationship of CO2, and PM2.5. During the study period, the measurements started at the northern part of the city, across the suburban area and ended at about 60 km in the southern Xiamen. The spatial distribution of CO2 along the road showed a high CO2 level in the central area of the city and low values in the outlying areas. Different CO2 concentrations were observed at different functional areas because of the differences in emissions from traffic and industry, the emission and absorption by vegetation, and meteorological conditions. The concentrations of CO, at different areas fell into the following order: areas with heavy traffic (477.33 micromol.mol-1 +/- 6. 11 micromol.mol-1 ) > commercial residential area (454. 95 micromol.mol-1 +/- 5.45 micromol.mol-1 ) > the naturalscenic spot (441.01 micromol.mol-1 +/- 6.24 micromol.mol-1 ) >cultivated land (436.79 micromol.mol-1 +/- 1.87 micromol.mol-1 ) > mountain woodlands (434.06 micromol.mol-1 +/-0.31 micromol.mol-1 ). The average CO, concentration in spring 2013 was measured to be 452.04 micromol mol -1 +/- 20.24 micro.mol. mol-1 with the maximum value of 533.10 micromol.mol-1 at the heavy traffic area in downtown Jiahe on April 12, 2013 and the minimum value of 413.25 micromol.mol-1 on April 10, 2013 at the mountain woodland, which is about 23 km away from the downtown area. The mountain woodland is surrounded by a reservoir and woods and regarded as the background area. The average CO2 concentration in fall 2013 was determined to be 451.80 micromol.mol-1 +/-21.56 micromol.mol-1 with the maximum value of 526.45 micromol.mol-1 at a heavy traffic area of Xiahe road in downtown, on November 19, 2013 and the minimum value of 415.01 p.mol.mol-' at the mountain woodland on November 10, 2013. This phenomenon was called "CO2 dome" by Idso in 1998. In addition, the CO2 concentrations tended to be the highest at night (22:00-01:00) and the lowest in afternoon (13:00-16:00). During overcast days, the CO, concentrations were generally higher than those on clear days. At different functional areas, differences between nighttime (22:00-01:00) and daytime (09:00-12:00 and 13:00-16:00) ranged from -0. 66-29.48 micromol.mol-1 in spring and from -4.01 micromol.mol-1-33.69 micromol.mol-1 in fall. The CO2 concentrations at the urban and the suburban areas were also different in spring and autumn and at different time of the day. The CO2 concentration was in significant correlation with PM2.5 (R =0.73, P < 0. 01) indicating the important impact of traffic pollution on the ambient CO2 concentration.