Abstract

AbstractNitrogen dioxide (NO2) fluxes were determined over a dry heather moor by the eddy‐correlation technique using a sonic anemometer and two Scintrex LMA‐3 chemiluminescent analysers. Using power spectral analysis virtually all the fluctuations in NO2 concentration were of frequencies less than 1 Hz at the measuring height of 5.32m. Even with the non‐ideal response of the LMA‐3 little information about NO2 concentration was lost. Co‐spectral analysis showed there was no loss of flux at high frequencies arising from the slow response of the LMA‐3.NO2 was deposited at a constant rate of 0.02 μg m‐2 ‐1 for nearly all of the measuring period. the deposition velocity maintained a mean value of 1 mm s‐1 throughout with minimum values nearing zero and maximum values of 3.5 mms‐1. There was no diurnal variation in canopy resistances to NO2. Mean values were 548 s m‐1 and 400 sm‐1 with and without the inclusion of several brief periods when the resistance increased markedly. Except for a brief period on 1 May the deposition was to the leaf cuticle as temperature and water stress caused the stomata to be closed. During the afternoon of 1 May there was some stomatal activity when the canopy resistance to water vapour fell and NO2 flux increased.Finally a simulation of the cumulative sampling method was performed on the data set as described in Businger and Oncley (1990). They calculated a constant of proportionality, b, and showed it to have a value of 0.6 when considering heat and water‐vapour fluxes. A value of b was calculated for NO2 flux using the data set presented here and was found to be 0.58.

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