Investigation of the atmospheric boundary layer depth variability and its impact on the ²²²Rn concentration at a rural site in France

Abstract

Continuous monitoring of the atmospheric boundary layer (ABL) depth (z i ) is important for investigations of trace gases with near-surface sources. The aim of this study is to examine the temporal variability of z i on both diurnal and seasonal time scales over a full year (2011) and relate these changes to the atmospheric 222 Rn concentrations (C Rn ) measured near the top of a 200 m tower at a rural site (Trainou) in France. Continuous z i estimates were made using a combination of lidar and hourly four-height carbon dioxide (CO 2 ) profile measurements. Over the diurnal cycle, the 180 m C Rn reached a maximum in the late morning as the growing ABL passed through the inlet height (180 m) transporting upward high C Rn air from the nocturnal boundary layer. During late afternoon, a minimum in the C Rn occurred mainly due to ABL-mixing. We argue that ABL dilution occurs in two stages: first, during the rapid morning growth into the residual layer, and second, during afternoon with the free atmosphere when z i has reached its quasi-stationary height (around 750 m in winter or 1700 m in summer). An anticorrelation (R 2 of À0.49) was found while performing a linear regression analysis between the daily z i growth rates and the corresponding changes in the C Rn illustrating the ABL-dilution effect. We also analyzed the numerical proportions of the time within a season when z i remained lower than the inlet height and found a clear seasonal variability for the nighttime measurements with higher number of cases with shallow z i (<200 m) in winter (67.3%) than in summer (33.9%) and spring (54.5%). Thus, this pilot study helps delineate the impact of z i on C Rn at the site mainly for different regimes of ABL, in particular, during the times when the z i is above the measurement height. It is suggested that when the z i is well below the inlet height, measurements are most possibly indicative of the residual layer 222 Rn, an important issue that should be considered in the mass budget approach.

Towards a Universal “Baseline” Characterisation of Air Masses for High- and Low-Altitude Observing Stations Using Radon-222

“…The application of radon in this way has been largely as a result of limitations in instrument accuracy, together with large data exclusion rates when radon thresholds much below 100 mBq m -3 were employed. However, relatively recent advances in continuous atmospheric radon measurement technology (e.g., Yver et al, 2011;Chambers et al, 2014;Pal et al, 2015;Williams and Chambers, 2015) have enabled far more stringent radon thresholds to be adopted (e.g., Chambers et al, 2015c), opening up new possibilities for baseline monitoring.…”

Wavelet modulus maxima method for on-line wavelength location of pulsed lidar in CO_2 differential absorption lidar detection

“…A singular point can be positioned by detection of the local modulus maxima in the wavelet transform maximum at fine scales. A wavelet has also been used for different lidar experiments in which atmospheric measurements are conducted [32]. There are some relevant concepts introduced to achieve an intensively understanding.…”

High-precision quasi-continuous atmospheric greenhouse gas measurements at Trainou tower (Orléans forest, France)

“…Full details of the instrumentation and the first time series of ABL depths can be found in Pal et al (2012Pal et al ( , 2014. …”