EMISSIONS OF TRACE GASES FROM CHINESE RICE FIELDS AND BIOGAS GENERATORS - CH4, N2O, CO, CO2, CHLOROCARBONS, AND HYDROCARBONS

We describe results from a research program to determine the emission rates of methane and of other environmentally significant gases from Chinese rice fields and biogas generators and to determine whether these sources contribute significantly to the global cycles of these trace gases or affect local and regional air quality. Experiments to determine the global flux of methane are still in progress. We conducted about 30 experiments and obtained some 900 individual measurements of trace gases emitted from rice fields and biogas generators around Chengdu in the Sichuan Province of China. These experiments were not sufficient to determine the global or annual emissions of methane from rice fields but fulfilled the other objectives of our program. The main findings are: (1) The biogas generators are not a significant source of methane on a global scale (≪1 tg/yr). (2) Rice fields release CO, CHCl3, and CO2 at observable rates. The emission rates of CO and CHCl3 are too small to contribute significantly to the global cycles of these gases. The CO2 emissions are very large, but because rice fields cycle carbon, there is probably to net flux of CO2 into the atmosphere when integrated over a few years. (3) Neither rice fields nor biogas generators contribute significantly to the local and regional CO and hydrocarbon pollution. (4) There is evidence, although not beyond reasonable doubt, that the rice fields take up some man-made chlorocarbons, particularly CCl3F, CCl2F2, CCl4, and CH3CCl3. These gases are implicated in the depletion of the ozone layer. © 1990.