利用便携式FTIR光谱仪研究环境大气中CO2浓度变化

高准确和高精度测量环境大气CO₂浓度，对于监测区域和城市温室气体的排放至关重要。基于傅里叶变换红外（FTIR）光谱技术，利用便携式FTIR光谱仪采集近红外太阳吸收光谱，基于非线性最小二乘算法，反演获得了2016年9月至2020年5月期间合肥地区环境大气的CO₂柱浓度。观测结果表明，CO₂气体的柱浓度有着明显的季节变化，在春季出现最大值，夏季下降速度快，秋季达到最小值。柱平均干空气混合比浓度XCO₂的日均值位于(401.23±0.60)和(418.41±0.31) ppm之间，而2017年观测的月均值有着6.96 ppm的季节幅值。并且，观测期间XCO₂呈现逐年增长的趋势，年平均增长率为(2.71±0.66) ppm·yr-1。为了验证便携式FTIR光谱仪观测的准确性和可靠性，我们将其观测结果与高分辨率FTIR仪器同步测量结果进行比较，发现观测的XCO₂的偏差均值为1.32 ppm，二者的相关系数r为0.97，两个数据显示高度一致性。同时将观测结果与GOSAT卫星数据作了横向比较，两个数据的平均偏差为(0.63±1.76) ppm，二者的相关系数r为0.86，显示出地基数据与卫星数据有高相关性。最后，将合肥站点2020年秋季观测数据与上海站点同期观测数据进行了比较，发现上海站点与合肥站点的CO₂柱浓度变化基本一致，合肥观测点的XCO₂日均值位于(415.09±0.84)和(417.80±0.67) ppm之间，上海观测点的XCO₂日均值位于(411.87±1.07)和(416.63±1.70) ppm之间，表明同步观测期间合肥的CO₂柱浓度略高于上海市。地基FTIR光谱仪的观测结果可为追踪合肥地区温室气体的碳源与碳汇提供基础数据。

Observation of Variations of Ambient CO2 Using Portable FTIR Spectrometer

Measurement of CO₂ concentration with high accuracy and precision is essential for monitoring local emission sources of greenhouse gases at regional and city scales. Based on Fourier transform spectroscopy and near-infrared solar absorption spectra collected by portable FTIR spectrometer, the column concentration of CO₂ in the Hefei area from September 2016 to May 2020 was retrieved using the nonlinear least-squares algorithm. As the observation results show, the column concentration of CO₂ has obvious seasonal variation, with the maximum value in spring, the fast decline in summer, and the minimum in autumn. The daily average value of XCO₂ is between (401.23±0.60) and (418.41±0.31) ppm, while the monthly average value shows a seasonal amplitude of 6.96 ppm during 2017. XCO₂ showed an increasing trend during the observation, with an annual growth rate of (2.71±0.66) ppm·yr-1. In order to verify the accuracy and reliability of portable FTIR spectrometer observations, we compared the observations with the high-resolution FTIR measurements. It is found that the mean deviation of XCO₂ was about 1.32 ppm, the linear fitting coefficient was 1.08±0.03, and the correlation coefficient r was 0.97. Further, our data are compared with GOSAT satellite data, the average deviation of the two data is (0.63±1.76) ppm, and the correlation coefficient r is 0.86, showing a high correlation between ground-based data and satellite data. Also, ground-based observations in Shanghai were compared with the simultaneous observations in Hefei. The results showed that the variation of XCO₂ in Shanghai is similar to our results. The daily average of XCO₂ in Shanghai is between (411.87±1.07) and (416.63±1.70) ppm, and the value is between (415.09±0.84) and (417.80±0.67) ppm in Hefei in autumn. It is found that XCO₂ in Hefei was slightly higher than that in Shanghai during the observation. The results provide the data for tracking carbon sources and sinks of greenhouse gases in the Hefei area.