Ds. Kim et al., CHARACTERIZATION OF NITROGEN-OXIDE FLUXES FROM SOIL OF A FALLOW FIELDIN THE CENTRAL PIEDMONT OF NORTH-CAROLINA, Atmospheric environment, 28(6), 1994, pp. 1129-1137
NO(x) emissions from soils may contribute to the formation of O3 in ru
ral areas, especially when there is substantial emissions of natural h
ydrocarbons from surrounding vegetation, such as in the southeastern U
nited States. Soil NO(x) flux measurements were made from 6 June 1992
to 7 July 1992 in the central Piedmont region of North Carolina (South
east Oxidants and Nitrogen intensive Analysis site, SONIA) in an effor
t to determine the role of natural emissions of NO(x) on rural atmosph
eric photochemistry. The overall average NO and NO2 emission rates, us
ing a dynamic chamber technique, were found to be 1.79 +/- 1.37 ng-N m
-2s-1 (range: 0.13 to 6.67 ng-N m-2s-1) and -1.07+/-0.87 ng-N m-2s-1 (
range: -6.71 to 3.16 ng-N m-2s-1), respectively. Over 85% of the NO2 f
lux measurements were negative indicating net deposition to the soil s
urface. No negative NO flux rates were observed. NO flux was correlate
d with soil temperature. There was a positive correlation between NO c
oncentration near the soil surface (approximately 50 cm) and NO flux (
r = 0.35). The NO compensation point (1.12 ppbv) was estimated from th
e relationship between NO emission rate and ambient NO concentrations
measured at 10 m. Both positive and negative vertical gradients of NO
concentration between 10 m and soil surface were detected. The positiv
e vertical gradients are indicative of NO transport to the site from p
olluted air masses. A significant negative correlation between NO flux
and ambient O3 concentration (r=0.66), however, supports the hypothes
is that soil emissions of NO contribute to local production Of O3 in r
ural areas.