On the use of radon for quantifying the effects of atmospheric stability on urban emissions

Abstract

Abstract.Radon is increasingly being used as a tool for quantifying stability influences on urban pollutant concentrations. Bulk radon gradients are ideal for this purpose, since the vertical differencing substantially removes contributions from processes on timescales greater than diurnal and (assuming a constant radon source) gradients are directly related to the intensity of nocturnal mixing. More commonly, however, radon measurements are available only at a single height. In this study we argue that single-height radon observations should not be used quantitatively as an indicator of atmospheric stability without prior conditioning of the time series to remove contributions from larger-scale "nonlocal" processes. We outline a simple technique to obtain an approximation of the diurnal radon gradient signal from a single-height measurement time series, and use it to derive a four category classification scheme for atmospheric stability on a "whole night" basis. A selection of climatological and pollution observations in the Sydney region are then subdivided according to the radon-based scheme on an annual and seasonal basis. We compare the radon-based scheme against a commonly used Pasquill-Gifford (P-G) type stability classification and reveal that the most stable category in the P-G scheme is less selective of the strongly stable nights than the radon-based scheme; this lead to significant underestimation of pollutant concentrations on the most stable nights by the P-G scheme. Lastly, we applied the radon-based classification scheme to mixing height estimates calculated from the diurnal radon accumulation time series, which provided insight to the range of nocturnal mixing depths expected at the site for each of the stability classes.

Soil heat flux and air temperature as factors of radon (Rn-222) concentration in the near-ground air layer

“…In most publications, Rn-222 has been used to study the atmosphere as a natural tracer of the processes of transport and dispersion of gases [5][6][7][8][9][10][11]. Rn-222 has also been used as an indicator of vertical mixing processes resulting in the atmospheric stability regime [12][13][14][15][16][17]. The temporal variability of the Rn-222 concentration with reference to the meteorological variables (such as wind velocity and direction, atmospheric pressure, air tempera- Abstract.…”

Improving the Representation of Cross-Boundary Transport of Anthropogenic Pollution in East Asia Using Radon-222

“…) is more than an order of magnitude less than observed at a flat, inland site (e.g., Chambers et al, 2015b), demonstrating the stabilising oceanic influence on Gosan mixing depths year round.…”

“…The maximum large-scale contributions occur during the day, when the ABL is well mixed, whereas the maximum local-scale contribution occurs at night, when the nocturnal inversion can completely isolate the near-surface air from the deeper layer above and therefore also from the larger-scale signal (e.g., Chambers et al, 2015b). The chemical compositions of the nocturnal boundary layer (NBL) and residual layer above evolve largely independently until sunrise, when convective mixing reconnects them.…”

Radon as a tracer of atmospheric influences on traffic-related air pollution in a small inland city

“…Thermally stable atmospheric conditions and their associated shallow mixing depths are renowned for impeding the dispersion of urban pollution (e.g. Duenas et al, 1996;Perrino et al, 2008;Belusˇic´et al, 2015;Grundstrom et al, 2015;Chambers et al, 2015a). They are also very problematic conditions for numerical models to accurately simulate, in large part due to limitations in model vertical resolution and the ability of parameterisations to accurately represent near-surface mixing processes (e.g.…”

“…Of the methods presently available to categorise the state of atmospheric stability (Pasquill and Smith, 1983;Perrino et al, 2001;Foken, 2006;Williams et al, 2013;Chambers et al, 2015a), here we employ near-surface measurements of the naturally occurring, radioactive atmospheric tracer Radon-222 (e.g. Chambers et al, 2015aChambers et al, , 2015b.…”