Measurements of Dry Deposition of No ₂ to A Dutch Heathland Using the Eddy‐Correlation Technique

Nitrogen dioxide (NO 2 ) 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 NO 2 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 NO 2 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. NO 2 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 NO 2 . 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 NO 2 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 NO 2 flux using the data set presented here and was found to be 0.58.