Several million hectares (ha) of soybeans are grown in alluvial soils of the Lower Mississippi River Valley. Using a diffusion chamber, nitrous oxide (N 2 O) flux to the atmosphere was measured over a growing season at a site in Louisiana. The average N 2 O flux over the soybean season was 2.2 AE 4.0 ng N 2 O-N cm À2 h À1 (over plants) and 2.1 AE 4.5 ng N 2 O-N cm À2 h À1 over the bare soil. Flux was governed by rainfall events. Maximum fluxes of 11.5 AE 2.1 ng N 2 O-N cm À2 h À1 , over plants, and 15.1 AE 5.5 ng N 2 O-N cm À2 h À1 over soil were measured following 15 inches (381 mm) of rainfall the week prior to flux measurements. The highest mean flux # ORDER REPRINTS (182 AE 222 ng N 2 O-N cm À2 h À1 ) was measured following harvest (stubble had been disked into soil) and a 4-inch (102 mm) rainfall event occurred just prior to flux measurements. Emission data showed that rainfall is important in predicting N 2 O flux from Mississippi alluvial soil used for soybean production. In order to properly quantify N 2 O flux, it is important to measure flux frequently over a series of rainfall events. Periodic flux measurements without factoring in rainfall may underestimate N 2 O flux to the atmosphere.

The concentration of atmospheric carbon monoxide, CO, was measured in the Amazonian rain forest. Air samples were collected at least three times a day during a continuous sequence of 36 days, from a height of 1.5 m above the ground. These surface CO measurements were part of a large binational field expedition to the Brazilian Amazon region, the ABLE 2B mission, a joint American-Brazilian effort to measure local concentrations of several species relevant to atmospheric chemistry. The time period of this experiment was April-May of 1987, in the local wet season. The measurement technique used was chromatographic separation followed by mercury vapor detection. The surface CO measurements obtained represent a comprehensive CO data set, unique in that the concentrations were measured immediately after collection, by a measurement system installed next to the sampling sites. The CO lab was set up at Ducke Forest Reserve, some 30 km north of the city of Manaus (3øS, 60øW). The results show a small but consistant diurnal variation of the CO concentration, with a maximum around noon. The average CO mixing ratio for the period was 102.9 _ 11.4 parts per billion by volume (ppbv), with most samples giving concentrations between 95 and 105 ppbv. On six occasions in April, large CO concentrations were observed during relatively short periods, and these were classified as pollution episodes associated with unusual wind conditions which probably brought air into the forest that had contact with the city of Manaus. No such episodes were seen during May. Simultaneous sampling inside the forest, under the canopy, and in the Ducke Forest clearing, show larger concentrations in the forest, by a few ppbv. This result is consistent with the direct measurement of the CO profile below the forest canopy, which gave a concentration gradient consistent with an upward flux of 4 x 10 TM CO molecules cm -2 s -I. INTRODUCTION A sensitive CO instrument was installed in the middle of the Amazonian rain forest, in early April 1987, as part of a large field expedition to the Amazon region in which American and Brazilian scientists were involved. The aim was to measure several atmospheric constituents important for atmospheric chemistry. Coordinators were the National Aeronautics and Space Administration (NASA) and the Brazilian Institute for Space Research (Instituto de Pesquisas Espaciais, or INPE). Several atmospheric gases were measured on board NASA's Electra aircraft, especially equipped with scientific instruments, but several other measurements were also conducted from the ground. This field mission, the Amazon Boundary Layer Experiment (ABLE) [McNeal et al., 1983], made its second visit to Amazonia in the 1987 wet season (April-May), and it was named the ABLE 2B mission. The previous campaign, the ABLE 2A experiment, took place in July-August of 1985, and several of its results were published in the Journal of Geophysical Research (volume 93, 1988). A general description of the ABLE 2A mission was presented by Harriss et al. [1988]. No spe...

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The manual harvest of sugar cane requires the burning of its foliage. This burning has strongly increased in Brazil after the National Alcohol Program was started which substituted automobile gasoline engines for alcohol engines. Presently, the source strength per unit area of this rural pollution is comparable to the well-known biomass burning source in Amazonia. The observed concentrations of CO and 0, in the rural area of the state of Sio Paulo during the 1988 burning season were twice as large as those reported from an aircraft experiment of 1985 for biomass burnings of the tropical rain forest. Results are reported from airplane measurements and from three fixed ground stations. Mixing ratios of ozone and carbon monoxide in the height range below 6 km are normally less than 40 and 100 ppbv, (parts per billion by volume), respectively, in the absence of burnings. A strong 0, and CO layer was observed during the burning period with peak concentrations of 80 ppbv of ozone and 580 ppbv of CO at about 2 km. The concentrations of CH, and CO, were also large, 1756 ppbv and 409 ppmv, respectively, at 1500 m. During the dry season period of the experiment, the ground based 0, average diurnal variations obtained at the rural sites were practically identical to the typical urban variation observed at Slo Jose dos Campos, with daytime ozone values between 45 and 60 ppbv. A second three-day airplane excursion to the surgar cane fields in the wet season of 1989 has produces results to be contrasted with the dry (burning) season of 1988 and 1989. Carbon monoxide concentrations were below 100 ppbv at all heights and ozone concentrations were around 30-40 ppbv. The maximum daytime concentrations at the ground station Bauru was 25 pphv of 0,, and at Jaboticabal it was 35 ppbv of O,, only one half of what was observed in the dry season.