Identifying persistent temperature inversion events in a subalpine basin using radon-222

Abstract

Abstract. One year of meteorological and atmospheric radon observations in a topographically complex subalpine basin are used to identify persistent temperature inversion (PTI) events. PTI events play a key role in public health due to the accumulation of urban pollutants that they cause. Two techniques are compared: a new radon-based method (RBM), based on single-height 222Rn measurements from a single centrally located station, and an existing pseudo-vertical temperature gradient method (TGM) based on observations from eight weather stations around the subalpine basin. The RBM identified six PTI events (four in winter, two in autumn), a subset of the 17 events identified by the TGM. The RBM was more consistent in its identification of PTI events for all seasons and more selective of persistent strongly stable conditions. The comparatively poor performance of the TGM was attributed to seasonal inconsistencies in the validity of the method's key assumptions (influenced by mesoscale processes, such as local drainage flows, nocturnal jets, and intermittent turbulence influence) and a lack of snow cover in the basin for the 2016–2017 winter period. Corresponding meteorological quantities for RBM PTI events (constituting 27 % of the autumn–winter cold season) were well characterized. PTI wind speeds in the basin were consistently low over the whole diurnal cycle (typically 0.2–0.6 m s−1). Suitability of the two techniques for air quality assessment was compared using hourly PM10 observations. Peak PM10 concentrations for winter (autumn) PTI events were underestimated by 13 µg m−3 (11 µg m−3) by the TGM compared with the RBM. Only the RBM indicated that nocturnal hourly mean PM10 values in winter PTI events can exceed 100 µg m−3, the upper threshold of low-level short-term PM10 exposure according to World Health Organization guidelines. The efficacy, simplicity, and cost effectiveness of the RBM for identifying PTI events has the potential to make it a powerful tool for urban air quality management in complex terrain regions, for which it adds an additional dimension to contemporary atmospheric stability classification tools. Furthermore, the long-term consistency of the radon source function will enable the RBM to be used in the same way in future studies, enabling the relative magnitude of PTI events to be gauged, which is expected to assist with the assessment of public health risks.

The determination of highly time resolved and source separated black carbon emission rates using radon as a tracer of atmospheric dynamics

“…Griffiths et al, 2013;Williams et al, 2013;Pal et al, 2015;Salzano et al, 2016;Vecchi et al, 2018), microclimate spatial variability (Chambers et al, 2016;Podstawczyńska, 2016) and impact assessment of atmospheric stability on local air pollution (Perrino et al, 2001;Chambers et al, 2015a;Chambers et al, 2015b;Crawford et al, 2016;Wang et al, 2016a;Williams et al, 2016). Good correlation, at least for the periods of thermally driven PBL convection, was observed in previous studies comparing effective MLH derived by the box model and MLH obtained by modelling approaches based on turbulence variables (Allegrini et al, 1994;Vecchi et al, 2018;Kikaj et al, 2019) or remote sensing techniques (sodar, lidar) (e.g. Salzano et al, 2016).…”

“…Salzano et al, 2016). Kikaj et al (2019) successfully identified persistent inversion events in the Ljubljana basin based on 222 Rn measurements. The emission pattern of gaseous traffic related air pollutants in Bern (Switzerland), estimated by a box-model based on radon tracer, with an included advection term, showed an excellent correlation with traffic density (Williams et al, 2016).…”

The determination of highly time-resolved and source-separated black carbon emission rates using radon as a tracer of atmospheric dynamics

“…Bottom-up emission inventories rely on information on the amount of used fuel combined with fuel-specific emission factors (e.g., Bond et al, 2007;Bond et al, 2013;Klimont et al, 2017). Although current emission inventories agree quite well on the main emission sources and regions, there exist significant uncertainties in the emission factors and activity data, used for emission calculation, with recent observationally constrained estimations much higher than the ones traditionally used (Sun et al, 2019).…”

“…A recently updated United States black carbon emission inventory (Sun et al, 2019) pointed out a decreasing trend of BC emissions from 1960 to 2000, dominated by the vehicle, industrial and residential sectors. Traffic-related BC emission primarily dominates particulate matter (PM) emission, especially in major cities (e.g., Pakkanen et al, 2000;Klimont et al, 2017). Recently, biomass combustion for residential heating has been promoted under the label of renewable fuel and additionally increased due to economic crises and increase in other fuel prices (Crilley et al, 2015;Denier van der Gon et al, 2015;Hovorka et al, 2015;Athanasopoulou et al, 2017).…”

Characterizing urban pollution variability in Central Poland using radon-222

“…Pasquil-Gifford schemes) or not well suited to the heterogeneous urban environment (Richardson number, Monin-Obukhov similarity theory). Consequently, this study employs a combination of two radon ( 222 Rn)-based techniques [5][6][7][8] for diurnal and synoptic timescale stability classifi cation. Radon's well-established history of application in atmospheric mixing studies [9][10][11][12] is testimony to the robustness and versatility of this tool.…”