Seasonal variation analysis of atmospheric CH4, N2O and CO2 in Tianjin offshore area

The concentrations of CH4, N2O and CO2 at the sea level were observed from November 2007 to August 2008 in order to study the greenhouse gases in the Tianjin offshore area of Bohai Sea. CH4 concentrations varied from 1.87 to 2.61 ppm with the highest value appearing in summer and the lowest in winter. The concentration range of N2O was 319.3 to 347.7 ppb, with the maximal value appearing in winter. CO2 was higher in the heating season than in non-heating season in this area. Concentrations of the three greenhouse gases in the study area exceeded the 2005 global background values. Backward trajectory model was used to analyze the sources. All three gases were influenced evidently by continental sources in the inshore area during the sampling periods. Every gas was compared with each other by correlation analysis, showing that the correlation of CO2 and N2O was more significant than to CH4 and their relationship with meteorological factors was consistent. It can be concluded these three greenhouse gases may be influenced by some similar sources, especially for CO2 and N2O.