SAMPLING NITROUS-OXIDE EMISSIONS FROM HUMID TROPICAL ECOSYSTEMS

Nitrous oxide (N2O), which is a long-lived greenhouse gas and the chie f source of nitric oxide (NO) in the stratosphere, is an important cat alyst in deletion of the ozone shield. The largest known natural or an thropogenic contribution to current increasing levels of atmospheric n itrous oxide is from the humid tropics. This research reports the meth odologies developed for monitoring N2O emissions from different humid tropical ecosystems over 2 years near Manaus, Brazil. Use of a double injection valve process for the chromatographic analysis of ambient le vels of N2O eliminated the need for sample preparation and backflushin g. The double injection valve process allows analysis of up to fifteen samples per hour for extended periods and provides excellent baseline stability and detector sensitivity. A closed, vented soil cover const ructed of PVC pipe was used to monitor N2O emissions from humid tropic al ecosystems. Dimensions of the soil cover affected estimates of N2O emissions from an abandoned pasture ecosystem. Flux estimates were hig hest when soil covers enclosed a minimum surface area of 300 cm(2) and a volume of 4 1. Storage of N2O samples (330, 915 and 1375 p.p.b.v.) in 125 ml glass serum bottles sealed with rubber septums for 48 hr had no effect on sample concentration, and samples retained 95% of their original concentration after 450 hr of storage. These methodologies ar e offered as simple, inexpensive means of developing N2O monitoring pr ogrammes in tropical ecosystems.