Measurements of molecular hydrogen and carbon monoxide on the Trainou tall tower

We present 2 yr (October 2008 to September 2010) of in situ measurements of molecular hydrogen (H-2) and carbon monoxide (CO) sampled at the tall tower of Trainou, France (47.96 degrees N, 02.11 degrees E, 131 masl, sampling height: 50, 100 and 180 m). Radon-222 (222Rn) measurements were added in May 2009. Background seasonal cycles, based on afternoon values, exhibit an amplitude of 45 and 60 ppb for H-2 and CO, respectively, for the three different heights (50, 100 and 180 m above ground). The vertical gradient also shows seasonal variations with a maximum (during the night) of 20 and 45 ppb for H-2 and CO, respectively. We also observe diurnal cycles for H-2 and CO for the three different heights. In the afternoon, the mixing ratios at the three different heights are similar and are comparable with maritime background stations, such as Mace Head (Ireland). The diurnal cycle of 222Rn follows the boundary layer height variations, with maximum values in the morning. Throughout the year but especially in summer and autumn, the H-2 mixing ratio shows nighttime depletion, with the lowest values at 06:00 UTC, due to soil uptake and the low boundary layer height. Using a simple box approach and the Radon-Tracer-Method, the H-2 deposition velocity is calculated for the catchment area of Trainou. We find a mean value for the H-2 deposition velocity of 2.6 +/- 0.9 10-2 cm s-1. During wintertime, H-2 and CO are sometimes strongly correlated leading to a H-2/CO ratio around 0.25. This ratio is lower than the ratio from traffic emissions, thus highlighting the mixing of sources in this area.