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4‐year records of gas chromatographic carbon dioxide and methane observations from the continental mountain station Schauinsland in the Black Forest (Germany) are presented. These data are supplemented by continuous atmospheric 222Radon observations. The raw data of CO2 concentration show a large seasonal cycle of about 16 ppm with monthly mean wintertime enhancements up to 10 ppm higher and summer minima up to 5 ppm lower than the maritime background level in this latitude. These offsets are caused by regional and continental scale CO2 sources and sinks. The mean CH4 concentration at Schauinsland is 31 ppb higher than over the Atlantic ocean, due to the European continent acting as a net source of atmospheric CH4 throughout the year. No significant seasonal cycle of methane has been observed. The long term CO2 and CH4 increase rates at Schauinsland are found to be similar to background stations in the northern hemisphere, namely 1.5 ppm CO2 yr−1 and 8 ppb CH4 yr−1. On the time scale of hours and days, the wintertime concentrations of all three trace gases are highly correlated, the mean ratio of CH4/CO2 is 7.8 ± 1.0 ppb/ ppm. The wintertime monthly mean concentration offsets relative to the maritime background level show a CH4/CO2 ratio of 6.5 ± 1.1 ppb/ ppm, thus, not significantly different from the short term ratio. Using the wintertime regressions of CO2 and 222Radon respectively CH4 and 222Radon we estimate winter time CO2flux densities of 10.4 ± 4.3 mmol CO2 m−2 h−1 (from monthly mean offsets) and 6.4 ± 2.5 mmol CO2 m−2 h−1 (from short term fluctuations) and winter time methane flux densities of 0.066 ± 0.034 mmol CH4 m−2 h−1 (from monthly mean offsets) and 0.057 ± 0.022 mmole CH4 m−2 h−1 (from short‐term fluctuations). These flux estimates are in close agreement to CO2 respectively CH4 emission inventories reported for Germany from statistical data.

We evaluate the capability of the global atmospheric transport model TM5 to reproduce observations of the boundary layer dynamics and the associated variability of trace gases close to the surface, using radon (222Rn), which is an excellent tracer for vertical mixing owing to its short lifetime (half-life) of 3.82 days. Focusing on the European scale, we compare the boundary layer height (BLH) in the TM5 model with observations from the NOAA Integrated Global Radiosonde Archive (IGRA) and in addition with ceilometer measurements at Cabauw (The Netherlands) and lidar BLH retrievals at Trainou (France). Furthermore, we compare TM5 simulations of 222Rn activity concentrations, using a novel, process-based 222Rn flux map over Europe (Karstens et al., 2015), with quasi-continuous 222Rn measurements from 10 European monitoring stations. The TM5 model reproduces relatively well the daytime BLH (within ~ 10–20 % for most of the stations), except for coastal sites, for which differences are usually larger due to model representation errors. During night, TM5 overestimates the shallow nocturnal BLHs, especially for the very low observed BLHs (< 100 m) during summer. The 222Rn activity concentration simulations based on the new 222Rn flux map show significant improvements especially regarding the average seasonal variability, compared to simulations using constant 222Rn fluxes. Nevertheless, the (relative) differences between simulated and observed daytime minimum 222Rn activity concentrations are larger for several stations (on the order of 50 %) compared to the (relative) differences between simulated and observed BLH at noon. Although the nocturnal BLH is often higher in the model than observed, simulated 222Rn nighttime maxima are larger at several continental stations, which points to potential deficiencies of TM5 to correctly simulate the vertical gradients within the nocturnal boundary layer, limitations of the 222Rn flux map, or issues related to the definition of the nocturnal BLH. At several stations the simulated decrease of 222Rn activity concentrations in the morning is faster than observed. In addition, simulated vertical 222Rn activity concentration gradients at Cabauw decrease faster than observations during the morning transition period, and are in general lower than observed gradients during daytime, which points to too fast vertical mixing in the TM5 boundary layer during daytime. Furthermore, the capability of the TM5 model to simulate the diurnal BLH cycle is limited due to the current coarse temporal resolution (3 hr/6 hr) of the TM5 input meteorology. Additionally, we analyze the impact of a new treatment of convection in TM5, based on the ECMWF reanalysis, leading to overall significantly lower (on the order of ~ 20 %) surface 222Rn activity concentrations during daytime compared to the current default convection scheme based on Tiedtke (1989). However, the performance of the model simulations compared to the 222Rn observations is very similar in terms of root mean square and correlation coefficient ...

Carbon dioxide and methane observations from the continental mountain station Kasprowy Wierch in the Tatra Mountains, southern Poland, are presented. They cover a six‐year period from 1994 to 2000. Significant year‐to‐year variability of CO2 concentration was observed. The seasonal cycles 1996–1997 were similar, with a peak‐to‐peak amplitude of the selected and smoothed CO2 record of approximately 20 ppm and no significant increase of the annual mean values. For 1998 and 1999 large increases of the annual mean values by 3.3 and 4.0 ppm per year, respectively, were observed. This increase was accompanied by a reduction of the seasonal amplitude of the smoothed record to approximately 15 ppm in 1998 and 16 ppm in 1999. In 2000 the seasonal amplitude increased again to a value similar as in 1996/1997, whereas the mean annual value remained close to that recorded for 1999. Similar features can also be traced in the selected and smoothed CO2 record for Schauinsland station, Germany, located ca. 1000 km west of Kasprowy Wierch. These similarities strongly suggest that both stations are capturing the same large‐scale European phenomena, most probably related to a disturbance of the CO2 cycle by the recent El Niño event. The mean CH4 mixing ratio at Kasprowy Wierch for the period 1996–1999 was about 30 ppb higher than over the Atlantic Ocean, confirming previous observations that the European continent is a net source of methane throughout the year. No significant seasonal cycle of methane has been observed at Kasprowy Wierch. The short‐term changes of CO2 and CH4 are strongly correlated during winter months: the average monthly mean slope of the linear relationship between CH4 and CO2 was 10.7 ± 0.3 ppbCH4 per ppmCO2. During summer months this strong correlation breaks down. Diurnal changes of CO2 and CH4 mixing ratios observed at Kasprowy Wierch are typical for continental mountain sites, with a distinct minimum of CO2 during afternoon hours in summer and maximum during winter. For CH4, diurnal cycles have similar shape throughout the year, with a broad maximum during daytime. The mean peak‐to‐peak amplitudes for summer (July) were 4.5 ppm for CO2 and 30 ppb for CH4, whereas during winter (February) they diminished to 1.5 ppm and 10 ppb, respectively.

A monitor for continuous observations of the atmospheric 222Rn daughter activity has been improved and successfully implemented in a field study in the European Taiga (Fyodorovskoye Forest Reserve). The α‐activity of the short‐lived 222Rn and 220Rn (212Pb) decay products, which are attached to aerosols, is accumulated on a quartz aerosol filter and assayed on line by α‐spectroscopy. The α‐activity from the 212Pb daughters is determined by spectroscopy and corrected for. This monitor is suitable to measure 222Rn activities at hourly resolution down to 0.5 Bq m−3 with an uncertainty well below ±20%. The prototype of this monitor is run in Heidelberg on the roof of the Institute's building about 20 m above ground. For this site, the atmospheric radioactive disequilibrium was determined between the 222Rn daughter 214Po and 222Rn, which has to be known in order to derive the atmospheric 222Rn activity with the static filter method. We derived a mean disequilibrium 214Po/222Rn = 0.704 ± 0.081 for various meteorological conditions through parallel 222Rn gas measurements with a slow pulse ionisation chamber. At the Russian field site, continuous activity observations were performed from July 1998 until July 2000 with half a year's interruption in summer/fall 1999. During intensive campaigns, a second monitor was installed at Fyodorovskoye at 15.6 m (July/August 1998), and at 1.8 m (July/August 1999 and October 1999) above ground. As expected, pronounced diurnal cycles of the 222Rn daughter activity were observed at all sites, particularly during summer when the vertical mixing conditions in the atmospheric surface layer vary strongly between day and night. The lower envelope of the continuous measurements at Fyodorovskoye and at Heidelberg changes on synoptic timescales by a factor of 4–10 due to long‐range transport changes between continental to more maritime situations. Generally, the 222Rn activity at 26.3 m height at Fyodorovskoye is lower by a factor of 2–3 compared to Heidelberg at 20 m above ground. This unexpected result is due to considerably lower 222Rn exhalation rates from the soils measured in the footprint of the Fyodorovskoye Forest tower compared to Heidelberg. With the inverted chamber technique 222Rn exhalation rates in the range 3.3–7.9 Bq m−2 h−1 were determined at Fyodorovskoye for summer 1998 and autumn 1999 (wet conditions with water table depths between 5 and 70 cm). Only during the very dry summer of 1999 the mean 222Rn exhalation rate increased by about a factor of five. All measured exhalation rates at the Fyodorovskoye Forest are considerably smaller by a factor of 2–10 compared to observations in the vicinity of Heidelberg (ca. 50–60 Bq m−2 h−1) and generally in Western Europe.