利用基于光腔衰荡光谱（ CRDS）测量技术，于2009年1月至2011年12月在龙凤山区域大气本底站对大气中CO2进行了在线观测．龙凤山CO2浓度日最低值出现在13∶00—16∶00，此时植被光合作用对CO2的吸收作用以及大气垂直运动导致的稀释作用最强．春、秋和冬季CO2浓度日最高值出现在7∶00—9∶00，夏季日最高值出现在3∶00．夏季日高值出现的早，是由于夏季日出时间较早，植物在5∶00左右就开始有光合作用，此时CO2浓度开始降低．一年中CO2月平均浓度低值出现在6—9月，高值出现在12月和1月，并在5月和10月分别出现1个次高值．CO2次高值是由于当地农村春季和秋季焚烧秸秆造成的．CO2年均值浓度从2009年的711±23 mg·L－1上升到2011年的723±25 mg·L－1，年平均增长率为0．89％．在夏季、冬季，当风向来自E?ESE?SE?SSE方位时CO2浓度较高，而当风向来自W?WNW?NW方位时CO2浓度较低．龙凤山区域大气本底站周边森林在夏季对CO2有很强的吸收，占夏季浓度的8．5％．
The background CO2 concentrations were continuously measured at Longfengshan regional atmospheric background station by Cavity Ring Down Spectroscopy system from 2009 to 2011. The results showed that the diurnal cycle of hourly average CO2 concentration displayed with the lowest value occurred at about 13∶00—16∶00, when the intensity of the photosynthesis of vegetable and the vertical air dilution are the strongest. Because of the earliest time of sunrise in summer and the CO2 consumption by the photosynthesis of vegetable, the highest concentration of CO2 occurred at the 3∶00, which is much earlier than that (7∶00—9∶00) in other seasons. The daily amplitude was the highest ( 92 mg·L-1 ) in summer and the daily amplitudes in other seasons were less than 8 × 10-6 . The monthly mean of CO2 concentration reached a high value in December or January and the lowest one in summer. Due to the agricultural biomass burning, the second peak of the monthly mean CO2 occurred in May and October. The annual mean of CO2 is 711 ± 23 mg·L-1 in 2009 and 723 ± 25 mg·L-1 in 2011, with an increase rate of 0.89%/yr. In summer and winter, surface wind from the sector of E?ESE?SE?SSE apparently increased the CO2 concentrations and surface wind from the sector of W?WNW?NW greatly decreased the CO2 concentration. The absorption effect of CO2 by the forest surrounding the station can be estimated by a value of 61 mg·L-1 , which is up to 8.5% of the average level of CO2 in summer.
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