Estimation of the molecular hydrogen soil uptake and traffic emissions at a suburban site near Paris through hydrogen, carbon monoxide, and radon‐222 semicontinuous measurements

Since June 2006, simultaneous semicontinuous measurements of tropospheric molecular hydrogen (H 2 ), carbon monoxide (CO), and radon‐222 ( 222 Rn) have been performed at Gif‐sur‐Yvette (Paris region), a suburban atmospheric measurement site in France. Molecular hydrogen mixing ratios range from 500 to 1000 ppb, CO mixing ratios vary from 100 to 1400 ppb, and 222 Rn concentrations fluctuate from 0 to 20 Bq m −3 . The H 2 seasonal cycle shows the expected pattern for the Northern Hemisphere with a maximum in spring and a minimum in autumn. We inferred a mean baseline value of 533 ppb with a peak‐to‐peak amplitude of 30 ppb. Carbon monoxide exhibits a seasonal cycle with a maximum in winter and a minimum in summer. The mean baseline value reaches 132 ppb with a peak‐to‐peak amplitude of 40 ppb. Radon‐222 presents weak seasonal variations with a maximum in autumn/winter and a minimum in spring/summer. The diurnal cycles of H 2 and CO are dominated by emissions from nearby traffic with two peaks during morning and evening rush hours. The typical H 2 /CO emission ratio from traffic is found to be 0.47 ± 0.08 on a molar basis (ppb/ppb). The radon tracer method is applied to nighttime H 2 observations to estimate the H 2 soil uptake of the nocturnal catchment area of our sampling site. The influences from nocturnal local anthropogenic combustion sources are estimated by parallel measurements of CO at 0.14 × 10 −5 g(H 2 ) m −2 h −1 . The mean inferred dry deposition velocity is 0.024 ± 0.013 cm s −1 with a seasonal amplitude of 40% at Gif‐sur‐Yvette.