Hydrogen soil deposition at an urban site in Finland

• Main Authors: T. Laurila, J. Hatakka, T. Aalto, M. Lallo
• Format: Article
• Language: English
• Published: Copernicus Publications 2009-11-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/9/8559/2009/acp-9-8559-2009.pdf

Hydrogen deposition velocities (<i>v<sub>d</sub></i>) were estimated by field chamber measurements and model simulations. A closed-chamber method was used for soil deposition studies in Helsinki, Finland, at an urban park inhabited by broad-leaved trees. Radon tracer method was used to estimate the <i>v<sub>d</sub></i> in nighttime when photochemical reactions were minimal and radon gas was concentrated in the shallow boundary layer due to exhalation from soil. A two-dimensional atmospheric model was used for the calculation of respective <i>v<sub>d</sub></i> values and radon exhalation rates. The <i>v<sub>d</sub></i> and radon exhalation rates were lower in winter than in summer according to all methods. The radon tracer method and the two-dimensional model results for hydrogen deposition velocity were in the range of 0.13 mm s<sup>−1</sup> to 0.93 mm s<sup>−1</sup> (radon tracer) and 0.12 mm s<sup>−1</sup> to 0.61 mm s<sup>−1</sup> (two-dimensional). The soil chamber results for <i>v<sub>d</sub></i> were 0.00 mm s<sup>−1</sup> to 0.70 mm s<sup>−1</sup>. Both models and chamber measurements revealed a relation between one week cumulative rain sum and deposition velocity. When precipitation events occurred a few days before the chamber measurements, lower <i>v<sub>d</sub></i> values were observed. A snow cover also lowered <i>v<sub>d</sub></i>.