Inferring <sup>222</sup>Rn soil fluxes from ambient <sup>222</sup>Rn activity and eddy covariance measurements of CO<sub>2</sub>

Abstract

Abstract. We present a new methodology, which we call Single Pair of Observations Technique with Eddy Covariance (SPOT-EC), to estimate regional-scale surface fluxes of 222 Rn from tower-based observations of 222 Rn activity concentration, CO 2 mole fractions and direct CO 2 flux measurements from eddy covariance. For specific events, the regional ( 222 Rn) surface flux is calculated from short-term changes in ambient ( 222 Rn) activity concentration scaled by the ratio of the mean CO 2 surface flux for the specific event to the change in its observed mole fraction. The resulting 222 Rn surface emissions are integrated in time (between the moment of observation and the last prior background levels) and space (i.e. over the footprint of the observations). The measurement uncertainty obtained is about ±15 % for diurnal events and about ±10 % for longerterm (e.g. seasonal or annual) means. The method does not provide continuous observations, but reliable daily averages can be obtained. We applied our method to in situ observations from two sites in the Netherlands: Cabauw station (CBW) and Lutjewad station (LUT). For LUT, which is an intensive agricultural site, we estimated a mean 222 Rn surface flux of (0.29 ± 0.02) atoms cm −2 s −1 with values > 0.5 atoms cm −2 s −1 to the south and southeast. For CBW we estimated a mean 222 Rn surface flux of (0.63 ± 0.04) atoms cm −2 s −1 . The highest values were observed to the south-west, where the soil type is mainly river clay. For both stations good agreement was found between our results and those from measurements with soil chambers and two recently published 222 Rn soil flux maps for Europe. At both sites, large spatial and temporal variability of 222 Rn surface fluxes were observed which would be impractical to measure with a soil chamber. SPOT-EC, therefore, offers an important new tool for estimating regional-scale 222 Rn surface fluxes. Practical applications furthermore include calibration of process-based 222 Rn soil flux models, validation of atmospheric transport models and performing regional-scale inversions, e.g. of greenhouse gases via the SPOT 222 Rntracer method.

Impacts of afternoon and evening sea‐breeze fronts on local turbulence, and on CO2 and radon‐222 transport

“…In particular, some SBFs from the N‐NE (15°–45°) induce a significant increase only at 20 m (Figure e), whereas they lead to decreases at 200 m. Furthermore, one SB event from the N‐NW (315°–345°) induces a large jump (∼ 1 Bq/m 3 ) at both 20 and 200 m agl. There is also a single event from the W‐SW, marked in this case by a significant fall in 222 Rn of more than 1 Bq/m 3 at 20 m and of around 0.5 Bq/m 3 at 200 m. These observations disagree with the estimates of van der Laan et al () for the surface fluxes of 222 Rn, and must therefore be explained by processes other than nearby emissions. First, the increase in wind speed enhances the dilution of 222 Rn and consequently produces a fall of its concentration (Ho and Measday, ; Vargas et al ), but, on the other hand, the transition from convective to stably stratified conditions builds up 222 Rn at lower levels.…”

A multi-model approach to monitor emissions of CO<sub>2</sub> and CO from an urban-industrial complex

“…The Cabauw site (51.97 • N, 4.93 • E) is situated 32 km east of the centre of Rotterdam and is considered a semi-urban site (van der Laan et al, 2016;Vermeulen et al, 2011). This means the sampled air masses are influenced by urban emissions, but less often than a truly urban Laan et al, 2009aLaan et al, , 2016. These four stations together describe a transect from the city towards rural areas.…”

“…On average the CO 2 mixing ratios are similar at all levels during well-mixed daytime conditions (Vermeulen et al, 2011), but a large gradient is observed for stable conditions when the 20 m level is highly affected by surface fluxes surrounding the tower. Similarly, Turnbull et al (2015) suggested that measurements closer to the surface are more sensitive to local fluxes, and therefore a higher level than 20 m is more suitable to obtain information on more remote fluxes. We choose the 60 m level observations to be able to compare them easily to the Lutjewad site.…”

“…Cities are major contributors to anthropogenic CO 2 and air pollutant emissions (Brioude et al, 2013;Turnbull et al, 2015;Velasco et al, 2014). Both the monitoring and modelling of urban/regional concentrations of CO 2 and coemitted air pollutants, such as CO and NO x , have therefore received a lot of attention (Brioude et al, 2013;Font et al, 2014;Huszar et al, 2016;Lac et al, 2013;Mays et al, 2009;McKain et al, 2012;Rayner et al, 2014;Ribeiro et al, 2016;Silva et al, 2013;Tolk et al, 2009;Wunch et al, 2009;Zhang et al, 2015).…”

“…However, their framework focused on regional (∼ 100-500 km), terrestrial fluxes. Several other studies focussed on urban scales (Boon et al, 2016;Bréon et al, 2015;Turnbull et al, 2015), but only few incorporated a Lagrangian model. For example, McKain et al (2012) and Lauvaux et al (2016) used a Lagrangian model to optimise urban fluxes of CO 2 , while Brioude et al (2013) compared simulated FLEXPART CO 2 , CO and NO x concentrations to small observational data sets from seven flights over Los Angeles.…”