[1] In this study deposition velocity (v d ) of atmospheric hydrogen to mineral and peat soils was measured in boreal forest environments in southern Finland using soil chamber measurement technique. v d was largest during the snow-free season (0.04-0.07 cm/s) and smallest during winter (0 -0.04 cm/s). Velocities decreased when soil temperature fell below 5°C, but deposition was observed also in near-zero temperatures. Deposition velocities to organic soil forest floor were larger than to mineral soil, but it was unclear whether this was due to the effect of carbon or the effect on soil porosity. Fluxes to both mineral and peat soils had similar temperature and soil moisture responses. In very dry and moist conditions v d decreased rapidly. Optimum soil moisture ranged from about 6 to 50 % of water by volume.

Abstract. Hydrogen deposition velocities (v d ) 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 v d 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 v d values and radon exhalation rates. The v d 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 v d 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 v d values were observed. A snow cover also lowered v d .

Methane mixing ratios have been continuously observed at Pallas, Finland since winter 2004. The seasonal variation in monthly means was ca. 40 ppb, showing largest mixing ratios in winter and also high values during late summer. Examination of back‐trajectories showed that the air masses with elevated methane mixing ratios arrived from continental Eastern and Central Europe while low methane mixing ratios were connected with Atlantic and Arctic air masses. During summer, air masses with highest mixing ratios arrived from Northwestern Russia indicating wetland sources, while the influence of southern emissions became more significant in winter. Methane was positively correlated with carbon dioxide and negatively correlated with ozone in winter. The average slope of the selected wintertime background hourly mean mixing ratios was 7.0 ± 1.2 ppb(CH4)/ppm(CO2). Nocturnal summertime low‐altitude measurements above a local wetland source indicated slopes of about 10 ± 1 ppb(CH4)/ppm(CO2). The different slopes reflect the differences in emission parameters.

Abstract.Atmospheric hydrogen (H 2 ) mixing ratios were observed over a one year period from summer 2007 to 2008 in Helsinki, Finland. Relatively stable background values of hydrogen were occasionally observed at the site, with minimum in October and maximum between March and May. High hydrogen mixing ratios occurred simultaneously with high carbon monoxide (CO) values and coincided with high traffic flow periods. Carbon monoxide and radon ( 222 Rn) were continuously monitored at the same site and they were used in estimation of the hydrogen emissions from traffic. The morning rush hour slope of H 2 / CO was in average 0.43±0.03 ppb (H 2 )/ppb (CO). After correction due to soil deposition of H 2 the slope was 0.49±0.07 ppb (H 2 )/ppb (CO). Using this slope and CO emission statistics, a road traffic emission of about 260 t (H 2 )/year was estimated for Helsinki in 2007.

Abstract. Hydrogen deposition velocities (v_d) 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 v_d in nighttime when photochemical reactions were minimal and radon gas was concentrated to shallow boundary layer due to exhalation from soil. A two-dimensional atmospheric model was used for calculation of respective v_d values and radon exhalation rate. v_d and radon exhalation rates were lower in winter than in summer according to all methods. The radon tracer method and two-dimensional model results for hydrogen deposition velocity were in the range of 0.13 mm s−1 to 0.90 mm s−1 (radon tracer) and 0.12 mm s−1 to 0.61 mm s−1 (two-dimensional). The soil chamber results for v_d were 0.00 mm s−1 to 0.70 mm s−1. Both models and chamber measurements revealed relation between one week cumulative rain sum and deposition velocity. Lower v_d values were usually measured in high soil moisture conditions. Precipitation occurring a few days before chamber measurements decreased v_d values. The snow cover also lowered v_d.