Keith
W.
Kisselle, Austin College, Sherman, TX USA, KKisselle@austincollege.edu
Richard
G.
Zepp, US EPA, Athens, GA USA, zepp.richard@epa.gov
(Presenting)
Roger
A.
Burke, US EPA, Athens, GA USA, burke.roger@epa.gov
Marirosa
Molina, US EPA, Athens, GA USA, molina.marirosa@epa.gov
Mercedes
Maria Cunha
Bustamante, Depto. Ecologia U. Brasilia Brasilia, Brazil, mercedes@unb.br
Previous field studies in pastures and native cerrado in central Brazil have indicated that surface plant litter and burn residues can be a major source of NOX [nitric oxide (NO) plus nitrogen dioxide (NO2)] and carbon monoxide (CO). Here we describe laboratory studies that provide more detailed information on factors that control these emissions. Litter samples were obtained from two native vegetation types in central Brazil, cerrado stricto sensu (20-50% canopy cover) and campo sujo (open scrubland) and from pastures (Brachiaria brizantha litter) located at an experimental farm near EMBRAPA Cerrados and at a cattle ranch (Fazenda Rio de Janeiro) that was 110 km north of Brasília. Some of these samples were combusted to produce an ash residue that also was used in the experiments. NOx and CO emissions from the litter and ash samples were investigated using flow-through chambers that were equipped to control the heating and irradiation of the samples. Both illumination under a solar simulator and heating in the absence of illumination (above ambient temperature of 28oC) induced increases in the gas emissions compared to emissions observed at 28oC in the dark. The largest increases were observed from the ash residues. Other experiments indicated that that the enhanced NOx emissions under illumination were primarily due to surface heating but the increased CO emissions were mainly caused by UV-induced litter photodegradation. The results indicate that NOx and CO flux measurements with opaque chambers can underestimate the emissions of these gases, especially in open, recently burned sites.