Scott Chambers

The Vertical Distribution of Radon in Clear and Cloudy Daytime Terrestrial Boundary Layers

Abstract Radon (222Rn) is a powerful natural tracer of mixing and exchange processes in the atmospheric boundary layer. The authors present and discuss the main features of a unique dataset of 50 high-resolution vertical radon profiles up to 3500 m above ground level, obtained in clear and cloudy daytime terrestrial boundary layers over an inland rural site in Australia using an instrumented motorized research glider. It is demonstrated that boundary layer radon profiles frequently exhibit a complex layered structure as a result of mixing and exchange processes of varying strengths and extents working in clear and cloudy conditions within the context of the diurnal cycle and the synoptic meteorology. Normalized aircraft radon measurements are presented, revealing the characteristic structure and variability of three major classes of daytime boundary layer: 1) dry convective boundary layers, 2) mixed layers topped with residual layers, and 3) convective boundary layers topped with coupled nonprecipitating ...

Separating remote fetch and local mixing influences on vertical radon measurements in the lower atmosphere

Two-point radon gradients provide a direct, unambiguous measure of near-surface atmospheric mixing. A 31-month data set of hourly radon measurements at 2 and 50 m is used to characterize the seasonality and diurnal variability of radon concentrations and gradients at a site near Sydney. Vertical differencing allows separation of remote (fetchrelated) effects on measured radon concentrations from those due to diurnal variations in the strength and extent of vertical mixing. Diurnal composites, grouped according to the maximum nocturnal radon gradient (Cmax), reveal strong connections between radon, wind, temperature and mixing depth on subdiurnal timescales. Comparison of the bulk Richardson Number (RiB) and the turbulence kinetic energy (TKE) with the radon-derived bulk diffusivity (KB) helps to elucidate the relationship between thermal stability, turbulence intensity and the resultant mixing. On nights with large Cmax, KB and TKE levels are low and RiB is well above the ‘critical’ value. Conversely, when Cmax is small, KB and TKE levels are high and RiB is near zero. For intermediate Cmax, however, RiB remains small whereas TKE and KB both indicate significantly reduced mixing. The relationship between stability and turbulence is therefore non-linear, with even mildly stable conditions being sufficient to suppress mixing.

Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim

ABSTRACT Radon concentrations measured between 2001 and 2008 in marine air at Cape Grim, a baseline site in north-western Tasmania, are used to constrain the radon flux density from the Southern Ocean. A method is described for selecting hourly radon concentrations that are least perturbed by land emissions and dilution by the free troposphere. The distribution of subsequent radon flux density estimates is representative of a large area of the Southern Ocean, an important fetch region for Southern Hemisphere climate and air pollution studies. The annual mean flux density (0.27 mBq m−2 s−1) compares well with the mean of the limited number of spot measurements previously conducted in the Southern Ocean (0.24 mBq m−2 s−1), and to some spot measurements made in other oceanic regions. However, a number of spot measurements in other oceanic regions, as well as most oceanic radon flux density values assumed for modelling studies and intercomparisons, are considerably lower than the mean reported here. The reported radon flux varies with seasons and, in summer, with latitude. It also shows a quadratic dependence on wind speed and significant wave height, as postulated and measured by others, which seems to support our assumption that the selected least perturbed radon concentrations were in equilibrium with the oceanic radon source. By comparing the least perturbed radon observations in 2002–2003 with corresponding ‘TransCom’ model intercomparison results, the best agreement is found when assuming a normally distributed radon flux density with σ=0.075 mBq m−2 s−1.

Estimating the Asian radon flux density and its latitudinal gradient in winter using ground-based radon observations at Sado Island

Terrestrial radon-222 flux density for the Asian continent, integrated over distances of 4500 km, is estimated in two 20. latitudinal bands centred on 48.8.N and 63.2.N. The evaluation is based on three years of wintertime radon measurements at Sado Island, Japan, together with meteorological and trajectory information. A selection of 18% of observations are suitable for evaluation of an analytical expression for the continental surface flux. Various meteorological assumptions are discussed; it is found that there is a substantial effect of increased complexity of the formulation on the flux estimates obtained. The distribution of spatially integrated radon flux over the Asian landmass is reported for the first time. Expressed as geometric means and 1±-ranges, estimated fluxes are 14.1 mBq m.2 s.1 (1±-range: 18 mBq m-2 s-1) and 8.4 mBq m-2 s-1 (1±-range: 10 mBq m-2 s-1) for the lower and higher latitude bands. These results constitute an annual minimum in flux densities for these regions, and are higher than previously reported. The existence of a latitudinal gradient in the continental radon source function is confirmed; the present estimate for Asia (-0.39 mBq m-2 s-1 per degree of latitude) is in agreement with the northern hemisphere terrestrial radon flux gradient proposed previously.

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

One year of radon, benzene and carbon monoxide (CO) concentrations were analysed to characterise the combined influences of variations in traffic density and meteorological conditions on urban air quality in Bern, Switzerland. A recently developed radon-based stability categorisation technique was adapted to account for seasonal changes in day length and reduction in the local radon flux due to snow/ice cover and high soil moisture. Diurnal pollutant cycles were shown to result from an interplay between variations in surface emissions (traffic density), the depth of the nocturnal atmospheric mixing layer (dilution) and local horizontal advection of cleaner air from outside the central urban/industrial area of this small compact inland city. Substantial seasonal differences in the timing and duration of peak pollutant concentrations in the diurnal cycle were attributable to changes in day length and the switching to/from daylight-savings time in relation to traffic patterns. In summer, average peak benzene concentrations (0.62 ppb) occurred in the morning and remained above 0.5 ppb for 2 hours, whereas in winter average peak concentrations (0.85 ppb) occurred in the evening and remained above 0.5 ppb for 9 hours. Under stable conditions in winter, average peak benzene concentrations (1.1 ppb) were 120% higher than for well-mixed conditions (0.5 ppb). By comparison, summertime peak benzene concentrations increased by 53% from well-mixed (0.45 ppb) to stable nocturnal conditions (0.7 ppb). An idealised box model incorporating a simple advection term was used to derive a nocturnal mixing length scale based on radon, and then inverted to simulate diurnal benzene and CO emission variations at the city centre. This method effectively removes the influences of local horizontal advection and stability-related vertical dilution from the emissions signal, enabling a direct comparison with hourly traffic density. With the advection term calibrated appropriately, excellent results were obtained, with high regression coefficients in spring and summer for both benzene (r2 ~0.90–0.96) and CO (r2 ~0.88–0.98) in the two highest stability categories. Weaker regressions in winter likely indicate additional contributions from combustion sources unrelated to vehicular emissions. Average vehicular emissions during daylight hours were estimated to be around 0.503 (542) kg km−2 h−1 for benzene (CO) in the Bern city centre.

Progress in the reduction of carbon monoxide levels in major urban areas in Korea.

Long-term trends in observed carbon monoxide (CO) concentrations were analyzed in seven major South Korean cities from 1989 to 2013. Temporal trends were evident on seasonal and annual timescales, as were spatial gradients between the cities. As CO levels in the most polluted cities decreased significantly until the early 2000s, the data were arbitrarily divided into two time periods (I: 1989-2000 and II: 2001-2013) for analysis. The mean CO concentration of period II was about 50% lower than that of period I. Long-term trends of annual mean CO concentrations, examined using the Mann-Kendall (MK) method, confirm a consistent reduction in CO levels from 1989 to 2000 (period I). The abrupt reduction in CO levels was attributed to a combination of technological improvements and government administrative/regulatory initiatives (e.g., emission mitigation strategies and a gradual shift in the fuel/energy consumption mix away from coal and oil to natural gas and nuclear power).

Estimating the near-surface daily fine aerosol load using hourly Radon-222 observations

We investigate the extent to which hourly radon observations can be used to estimate daily PM2.5 loading near the ground. We formulate, test and apply a model that expresses the mean daily PM2.5 load as a linear combination of observed radon concentrations and differences on a given day. The model was developed using two consecutive years of observations (2007–2008) at four sites near Sydney, Australia, instrumented with aerosol samplers and radon detectors. Model performance was subsequently evaluated against observations in 2009. After successfully reproducing mean daily radon concentrations (r2≥0.98), we used the model to estimate daily PM2.5 mass, as well as that of selected elements (Si, K, Fe, Zn, H, S and Black Carbon). When parameterizing the model for elemental mass estimates the highest r2 values were generally obtained for H, BC, K and Si. Separating results by season, the r2 values for K and BC were higher in winter for all sites, a period of time where higher concentrations of these elements are seen and a rapid estimation tool would be of particular benefit. The best overall results were obtained in winter for H and BC [r2 = 0.50, 0.68, 0.70, 0.63 (H) and 0.57, 0.57, 0.78, 0.44 (BC)], respectively for Warrawong, Lucas Heights, Richmond and Muswellbrook. Evaluation of model PM2.5 estimates was most successful for days with typical aerosol loads; loads were usually underestimated for, the less frequent, high–to–extreme pollution days. The best elemental results were obtained for BC at Richmond in winter (r2 = 0.68). However, for Warrawong and Lucas Heights r2 values increased from 0.26 to 0.60, and from 0.33 to 0.73, respectively, when several particularly high concentration events were excluded from the analysis. The model performed best at Richmond, an inland site with relatively flat terrain. However, model parameters need to be evaluated for each site.

Toward a better understanding of the impact of mass transit air pollutants on human health

Globally, modern mass transport systems whether by road, rail, water, or air generate airborne pollutants in both developing and developed nations. Air pollution is the primary human health concern originating from modern transportation, particularly in densely-populated urban areas. This review will specifically focus on the origin and the health impacts of carbonaceous traffic-related air pollutants (TRAP), including particulate matter (PM), volatile organic compounds (VOCs), and elemental carbon (EC). We conclude that the greatest current challenge regarding urban TRAP is understanding and evaluating the human health impacts well enough to set appropriate pollution control measures. Furthermore, we provide a detailed discussion regarding the effects of TRAP on local environments and pedestrian health in low and high traffic-density environments.

Statistical analysis of Seoul air quality to assess the efficacy of emission abatement strategies since 1987

The combined influences of recent mitigation measures on urban air quality have been assessed using hourly observations of the criteria air pollutants (NO, NO2, O3, CO, and SO2) made from the Yongsan district of Seoul, Korea, over 26years (1987 to 2013). A number of data selection criteria are proposed in order to minimize variability associated with temporal changes (at diurnal, weekly, and seasonal timescales) in source strengths, their spatial distribution, and the atmospheric volume into which they mix. The temporal constraints required to better characterize relationships between observed air quality and changes in source strengths in Seoul were identified as: (i) a 5-hour diurnal sampling window (1300-1700h), (b) weekday measurements (Monday to Friday only), and (c) summer measurements (when pollutant fetch is mostly Korea-specific, and mean wind speeds are the lowest). Using these selection criteria, we were able to closely relate long-term trends identified in criteria pollutants to a number of published changes to traffic-related source strengths brought about by mitigation measures adopted over the last 10-15years.

Radon-based technique for the analysis of atmospheric stability – a case study from Central Poland

Abstract An economical and easy-to-implement technique is outlined by which the mean nocturnal atmospheric mixing state (“stability”) can be assessed over a broad (city-scale) heterogeneous region solely based on near-surface (2 m above ground level [a.g.l.]) observations of the passive tracer radon-222. The results presented here are mainly based on summer data of hourly meteorological and radon observations near Łodź, Central Poland, from 4 years (2008–2011). Behaviour of the near-surface wind speed and vertical temperature gradient (the primary controls of the nocturnal atmospheric mixing state), as well as the urban heat island intensity, are investigated within each of the four radon-based nocturnal stability categories derived for this study (least stable, weakly stable, moderately stable, and stable). On average, the most (least) stable nights were characterized by vertical temperature gradient of 1.1 (0.5)°C·m−1, wind speed of ~0.4 (~1.0) m·s−1, and urban heat island intensity of 4.5 (0.5)°C. For sites more than 20 km inland from the coast, where soils are not completely saturated or frozen, radon-based nocturnal stability classification can significantly enhance and simplify a range of environmental research applications (e.g. urban climate studies, urban pollution studies, regulatory dispersion modelling, and evaluating the performance of regional climate and pollution models).