Determination of HNO₃ dry deposition by modified Bowen ratio and aerodynamic profile techniques

Modified Bowen ratio and aerodynamic profile techniques based on the constant flux approach were utilized to derive the deposition fluxes and deposition velocities (vd) of gaseous nitric acid from measurements made during two joint field experiments over low vegetation (grassland, LOVENOX, Halvergate, UK, September 1989) and over a wheat canopy (ecosystem wheat, Manndorf, Germany, July 1990). Both micrometeorological methods are discussed in more detail and in context with the flux-resistance analogy to provide a complete conceptual evaluation guide for HNO₃ dry deposition analysis. Daytime dry deposition of nitric acid was found to be fast with an average vd of 2.2 ± 1.2 cm s^-1 and a range of 0.6 to 5.0 cm s^-1. The derived deposition velocities are in broad agreement with estimates of other authors. The data have also been used to check sublayer Stanton numbers which are of basic importance in determining the viscous sublayer resistance yet not well quantified.