Hydrogen soil deposition at an urban site in Finland
Abstract. Hydrogen deposition velocities (vd) 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 vd 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 vd values and radon exhalation rates. The vd 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−1 to 0.93 mm s−1 (radon tracer) and 0.12 mm s−1 to 0.61 mm s−1 (two-dimensional). The soil chamber results for vd were 0.00 mm s−1 to 0.70 mm s−1. 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 vd values were observed. A snow cover also lowered vd.