| As carbon monoxide, methane and nitrous oxide are active in atmospheric chemical processes, a change of the concentration of these species will affect the equilibrium of atmospheric chemical reactions and the balance of atmospheric species, implying the change of many other minor gases, including some pollutants such as ozone. In addition, the change of the concentrations of CH4 and N2O as greenhouse effect gases will impact on the global climate. Therefore the study of atmospheric CO, CH4, and N2O is very significant for the study of climate and atmospheric environment.The description of the infrared grating spectrometer of moderate resolution is given, and the principle and the method of retrieving CO column amount from the measured solar infrared absorption spectra are also presented in detail. The random error analysis of the method gives the relative deviation of 8%-10%) for the method of deriving CO. It shows that the column content of CO and other atmospheric minor gases can be well derived using this method, and the retrieval algorithm is very simple and effective.The CO, water vapor, CH4 and other minor gases have been measured in Beijing since 1996 by LAGEO, Institute of Atmospheric Physics, Chinese Academy of Sciences, using an infrared grating spectrometer of moderate resolution. The observation site locates on the roof of the building of the Institute of Atmospheric Physics located in the right north between the 3rd and 4th circles. The CO and water vapor column contents have been measured during autumn since 1996, summers of 1997 and 1999, and through 2003, and CH4 column content for autumns of 1996, 1998, 2001 and 2002. Besides, measurement of these minor gases and N2O has been conducted in the same site during autumn of 1992. In this paper, the characteristics and the variation of these minor gases in the urban city (Beijing) was studied by means of the data process and analysis and the discussion was made for the factors related to the variation. The main results are as follows:1. CO and water vapor column contents retrieved from the solar absorption spectra are well related with the surface CO concentration and surface dew point respectively. Therefore, the CO column amount can indicate the atmospheric contamination close to the surface.2. The monthly average of CO column content over Beijing urban area ranges between 0.1 and 0.2 atm-cm in autumn during the period of 1996~2003, and CH4 between 1.17 and 1.47 atm-cm. N2O column content measured in 1992 is somewhatstable, the average value of which is 0.248 atmcm.3. The monthly average just for November of CO column content as high as 0.185 atm-cm was observed in 1998, which is the highest value compared to Monthly averages for November of the other years. The increasing CO abundances coincide with the events of widespread wildfires between late 1997 and 1998. Afterwards, CO column came back to common level (0.15 atmcm) in 1999. The minimum, 0.122 atmcm was observed in 2001. The average of CH4 column contents of 2001 and 2002 (about 1.18 atmcm) are lower than those of 1996 (1.47 atmcm) and 1998 (1.38 atmcm), which may be caused by the decreasing emission source, or by the variation of atmospheric CO and OH concentrations.4. CO column content is characterized by seasonal variations with the maximum in winter and the minimum in summer, and opposite variation was observed for water vapor in Beijing.5. Seasonal variation of CO total column in Beijing is greatly affected by the major CO source with similar season variation. The changes in CO column amount are closely related to meteorological conditions, mainly including atmospheric stability, wind speed and wind direction. |
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