ANSTO :: Browsing by Author "Crawford, J"

Browsing by Author "Crawford, J"

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Accelerator based ion beam analysis techniques contribute to a better understanding of long range fine particle pollution in Asia
(International Atomic Energy Agency, 2012-09-15) Cohen, DD; Stelcer, E; Crawford, J; Bac, VT
Fine-particle pollution in large populated Asian cities can be very high compared with internationally accepted health goals. Much of this fine-particle pollution is produced by motor vehicles, fossil-fuel combustion, industrial processes and even windblown soils from desert regions. As part of a long term project in the Asian region with support from the IAEA, ANSTO has been using nuclear techniques not only to characterize fine-particle pollution, but also to quantify their sources and origins within Vietnam. © International Atomic Energy Agency
Alternative least squares methods for determining the meteoric water line, demonstrated using GNIP data
(Elsevier, 2014-11-01) Crawford, J; Hughes, CE; Lykoudis, S
The relationship between δ2H and δ18O in precipitation at a site, known as the local meteoric water line (LMWL), is normally defined using an ordinary least squares regression (OLSR). However, it has been argued that this form of minimisation is more appropriate when a predictive model is being developed (and there are no measurement errors associated with the independent variable) and that orthogonal regression, also known as major axis regression (MA), or reduced major axis regression (RMA) may be better suited when a relationship is being sought between two variables which are related by underlying physical processes. The slope of the LMWLs for the GNIP data is examined using the three linear regressions, and the corresponding precipitation weighted regressions. The MA and RMA regressions generally produced larger slopes, with the largest differences for oceanic islands and coastal sites. The difference between the various methods was the least for continental sites. In all considered cases, both for the standard and precipitation weighted regressions, the slope produced by RMA was in between those determined by OLSR and MA, with OLSR producing the smaller slope. Further, the results of both RMA and precipitation weighted RMA were less sensitive to the removal of outliers and values with high leverage statistic. The results indicate that when a good linear relationship exists between δ2H and δ18O, all considered regressions result in a close fit. When the values are distributed within circles or ellipses on the δ18O–δ2H bivariate plot, as would appear in coastal and oceanic sites from first stage rainout, care needs to be taken as to which regression is utilised. However, in some of these cases, it appears the precipitation weighted MA (and in some cases MA) produces large slopes. In these cases the average Root Mean Sum of Squared Error (rmSSEav) value of the fit can be used as a guide of the suitability of the MA and PWMA for each site. Where the slope of the PWRMA was significantly different to the slope of the OLSR regression (22% of sites; dominated by coastal, island and Mediterranean locations), we believe PWRMA is more suitable.© 2014 Elsevier B.V.
Analysis of a decade of Asian outflow of PM10 and TSP to Gosan, Korea: also incorporating Radon-222
(Elsevier B.V., 2015-05) Crawford, J; Chambers, SD; Kang, CH; Griffiths, AD; Kim, WH
Ten years of aerosol and Radon–222 (radon) data from Gosan, Korea, were analyzed. Seasonal cycles were strongly linked to changes in fetch and time of year. We estimated that 7.21 t/m y of PMio aerosol pass Gosan in the atmospheric boundary layer, increasing annually by 0.3 t/m y. Contributions to aerosol loading were characterized by fetch: South China, North China, Korea and Japan. While the highest, and most variable, contributions typically originated from South China, these air masses contributed to only 6% of the overall dataset. PM10 distributions were broader from South and North China than for Korea or Japan, reflecting differences in natural/anthropogenic soil sources, and number/distribution of large point sources. Employing radon to select air masses more representative of targeted fetch regions typically resulted in greater reported pollutant concentrations and rates of change over the decade. Estimated rates of PM10 increase from North China and Korea over the decade were 1.4 and 0.9 μg/m3 y, respectively. Total suspended particulate (TSP) elemental analysis indicated that the (non–sea–salt) nss–SO42− content of aerosols has been gradually increasing over the past decade and more recently an increase in NO3− was seen. However, on average, rates of increase in nss–SO42− have reduced since 2007, which were higher in South than North China. © 2020 Elsevier B.V.
The application of IBA techniques to air pollution source fingerprinting and source apportionment
(Elsevier Science BV, 2014-01-01) Cohen, DD; Stelcer, E; Atanacio, AJ; Crawford, J
IBA techniques have been used to measure elemental concentrations of more than 20 different elements found in fine particle (PM2.5) air pollution. These data together with their errors and minimum detectable limits were used in Positive Matrix Factorisation (PMF) analyses to quantitatively determine source fingerprints and their contributions to the total measured fine mass. Wind speed and direction back trajectory data from the global HYSPLIT codes were then linked to these PMF fingerprints to quantitatively identify the location of the sources. © 2014, Elsevier Ltd.
Application of positive matrix factorisation, multi-linear engine and back trajectory techniques to the quantification of coal-fired power station pollution in metropolitan Sydney
(Pergamon Elsevier Science Ltd, 2012-12-01) Cohen, DD; Crawford, J; Stelcer, E; Atanacio, AJ
Over 900 fine particle Teflon filters were collected within the Sydney Basin between 1 January 2001 and 31 December 2011 and analyzed using simultaneous PIXE, PIGE, RBS and PESA techniques to determine 21 different elements between hydrogen and lead. These elements were used in positive matrix factorization (PMF) and multi-linear engine (ME) techniques together with HYSPLIT wind back trajectory techniques to quantitatively determine source fingerprints and their contributions from coal-fired power stations. The power stations were many kilometers outside the greater Sydney metropolitan area but still had a significant impact on the fine particle mass loadings measured at the sampling site within this metropolitan area. The PM2.5 eleven year average mass at the sampling site was 6.48 mu g m(-3). The corresponding ammonium sulfate estimate was 1.65 mu g m(-3) or 26% of the PM2.5 mass. By applying back trajectory data and (ME) analysis methods, two power related fingerprints, secondary sulfate (2ndryS-Power) and aged industrial sulfur (IndSagedPower) were determined. These two power related fingerprints were responsible for between 14 and 18% of the total PM2.5 mass and 34-47% of the total sulfate measured at the sampling site. That is on average somewhere between a third and a half of all the sulfate measured in the greater Sydney region could be attributed to coal-fired power station emissions. © 2012, Elsevier Ltd.
Application of the pore water stable isotope method and hydrogeological approaches to characterise a wetland system
(Copernicus Publications, 2018-12-06) David, K; Timms, W; Hughes, CE; Crawford, J; McGeeney, D
Three naturally intact wetland systems (swamps) were characterised based on sediment cores, analysis of surface water, swamp groundwater, regional groundwater and pore water stable isotopes. These swamps are classified as temperate highland peat swamps on sandstone (THPSS) and in Australia they are listed as threatened endangered ecological communities under state and federal legislation. This study applies the stable isotope direct vapour equilibration method in a wetland, aiming at quantification of the contributions of evaporation, rainfall and groundwater to swamp water balance. This technique potentially enables understanding of the depth of evaporative losses and the relative importance of groundwater flow within the swamp environment without the need for intrusive piezometer installation at multiple locations and depths. Additional advantages of the stable isotope direct vapour equilibration technique include detailed spatial and vertical depth profiles of δ18O and δ2H, with good accuracy comparable to other physical and chemical extraction methods. Depletion of δ18O and δ2H in pore water with increasing depth (to around 40–60 cm depth) was observed in two swamps but remained uniform with depth in the third swamp. Within the upper surficial zone, the measurements respond to seasonal trends and are subject to evaporation in the capillary zone. Below this depth the pore water δ18O and δ2H signature approaches that of regional groundwater, indicating lateral groundwater contribution. Significant differences were found in stable pore water isotope samples collected after the dry weather period compared to wet periods where recharge of depleted rainfall (with low δ18O and δ2H values) was apparent. The organic-rich soil in the upper 40 to 60 cm retains significant saturation following precipitation events and maintains moisture necessary for ecosystem functioning. An important finding for wetland and ecosystem response to changing swamp groundwater conditions (and potential ground movement) is that basal sands are observed to underlay these swamps, allowing relatively rapid drainage at the base of the swamp and lateral groundwater contribution. Based on the novel stable isotope direct vapour equilibration analysis of swamp sediment, our study identified the following important processes: rapid infiltration of rainfall to the water table with longer retention of moisture in the upper 40–60 cm and lateral groundwater flow contribution at the base. This study also found that evaporation estimated using the stable isotope direct vapour equilibration method is more realistic compared to reference evapotranspiration (ET). Importantly, if swamp discharge data were available in combination with pore water isotope profiles, an appropriate transpiration rate could be determined for these swamps. Based on the results, the groundwater contribution to the swamp is a significant and perhaps dominant component of the water balance. Our methods could complement other monitoring studies and numerical water balance models to improve prediction of the hydrological response of the swamp to changes in water conditions due to natural or anthropogenic influences. © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License.
Assessing the impact of atmospheric stability on locally and remotely sourced aerosols at Richmond, Australia, using Radon-222
(Elsevier, 2015-12-13) Crawford, J; Chambers, SD; Cohen, DD; Williams, AG; Griffiths, AD; Stelcer, E
A flexible radon-based scheme for the classification of nocturnal stability regimes was used for the interpretation of daily-integrated PM2.5 aerosol observations collected at Richmond, Australia, between 2007 and 2011. Source fingerprint concentrations for the dominant locally and remotely sourced aerosols were analysed by nocturnal radon stability category to characterise the influences of day-to-day changes in daily integrated atmospheric mixing. The fingerprints analysed included: smoke, vehicle exhaust, secondary sulfate and aged industrial sulfur. The largest and most consistent stability influences were observed on the locally sourced pollutants. Based on a 5-year composite, daily integrated concentrations of smoke were almost a factor of 7 higher when nocturnal conditions were classed as “stable” than when they were “near neutral”. For vehicle emissions a factor of 4 was seen. However, when the winter months were considered in isolation, it was found that these factors increased to 11.5 (smoke) and 5.5 (vehicle emissions) for daily average concentrations. The changes in concentration of the remotely sourced pollutants with atmospheric stability were comparatively small and less consistent, probably as a result of the nocturnal inversion frequently isolating near-surface observations from non-local sources at night. A similar classification was performed using the commonly-adopted Pasquill–Gifford (PG) stability typing technique based on meteorological parameters. While concentrations of fingerprints associated with locally-sourced pollutants were also shown to be positively correlated with atmospheric stability using the PG classification, this technique was found to underestimate peak pollutant concentrations under stable atmospheric conditions by almost a factor of 2. © 2015, Elsevier Ltd.
Assessing the impact of synoptic weather systems on air quality in Sydney using Radon 222
(Elsevier, 2023-02-15) Crawford, J; Chambers, SD; Williams, AG
The state of the atmosphere can affect the degree of dilution of emitted pollutants, and similar local and diurnal meteorological conditions can be grouped according to prevailing synoptic scale weather systems. Traditionally, various methods have been used to classify atmospheric conditions. Here we investigate the use of Radon-222 (radon) for the classification of weather systems and determine the degree of dilution under different synoptic conditions. Air quality data was analyzed in Richmond Australia over a 13-year period. Radon was used to determine 5 nocturnal stability categories numbered 0 to 4, with 0 capturing times of fast-changing fetch influences, and 1–4 representing increasing conditions of nocturnal stability (1: near neutral, to 4: strongly stable). These categories were then related to prevailing synoptic weather systems. It was found that increasing radon-derived stability categories were associated with reducing intensity of frontal systems traversing southern Australia and extending into the Southern Ocean, with stability category 4 associated with blocking high pressure systems located to the east of the site. The median nocturnal wind speeds and mixing layer heights decreased as we moved from stability category 0 to 4, indicating that the mixing volumes for pollutants released into the atmosphere from surface sources was progressively getting smaller. This decreasing dilution from stability category 0 to 4 resulted in strongly increasing median pollutant concentrations. However, on diurnal and seasonal time scales, differences were observed which could be attributed to changes in emission rates. Our results show that when investigating the impact of air quality mitigation strategies, any variations in meteorological conditions during the comparison periods needs to be considered in addition to changes in pollution emission rates, and that near-surface radon observations and the ventilation coefficient are a convenient and effective tool for this purpose. © 2022 Published by Elsevier Ltd. All rights reserved.
Atmospheric stability effects on potential radiological releases at a nuclear research facility in Romania: characterising the atmospheric mixing state
(Elsevier, 2016-04-01) Chambers, SD; Galeriu, D; Williams, AG; Melintescu, A; Griffiths, AD; Crawford, J; Dyer, LL; Duma, M; Zorila, B
A radon-based nocturnal stability classification scheme is developed for a flat inland site near Bucharest, Romania, characterised by significant local surface roughness heterogeneity, and compared with traditional meteorologically-based techniques. Eight months of hourly meteorological and atmospheric radon observations from a 60 m tower at the IFIN-HH nuclear research facility are analysed. Heterogeneous surface roughness conditions in the 1 km radius exclusion zone around the site hinder accurate characterisation of nocturnal atmospheric mixing conditions using conventional meteorological techniques, so a radon-based scheme is trialled. When the nocturnal boundary layer is very stable, the Pasquill–Gifford “radiation” scheme overestimates the atmosphere's capacity to dilute pollutants with near-surface sources (such as tritiated water vapour) by 20% compared to the radon-based scheme. Under these conditions, near-surface wind speeds drop well below 1 m s−1 and nocturnal mixing depths vary from ∼25 m to less than 10 m above ground level (a.g.l.). Combining nocturnal radon with daytime ceilometer data, we were able to reconstruct the full diurnal cycle of mixing depths. Average daytime mixing depths at this flat inland site range from 1200 to 1800 m a.g.l. in summer, and 500–900 m a.g.l. in winter. Using tower observations to constrain the nocturnal radon-derived effective mixing depth, we were able to estimate the seasonal range in the Bucharest regional radon flux as: 12 mBq m−2 s−1 in winter to 14 mBq m−2 s−1 in summer. © 2016, Elsevier Ltd.
Australian rainfall isotope variability and its relationship with groundwater
(Copernicus Publications, 2017-07-10) Hughes, CE; Crawford, J; Cendón, DI; Meredith, KT; Hollins, SE
Rainfall stable isotope composition varies dramatically across the Australian continent. Using monthly deuterium and oxygen-18 data from 15 Global Network of Isotopes in Precipitation (GNIP), sites the underlying causes for the spatial and temporal variability have been investigated. Because of the island nature of Australia, moisture originates from the Indian Ocean to the west and the Pacific Ocean to the east, and is dominated by the monsoon and tropical cyclones to the north and frontal and low pressure systems to the south. Simple rainfall amount or temperature relationships don’t explain what is observed over this low-elevation continent because of the huge spatial variability in moisture source and synoptic processes. However, latitude, elevation and continentality were found to have some influence on the isotopic average at the 15 sites. Using relationships developed with data from the 15 GNIP sites and additional data from higher elevation sites, an isoscape has been developed. This is used to investigate what drives groundwater recharge at a variety of locations across Australia. In many regions groundwater recharge can be linked isotopically to extreme high rainfall events such as tropical cyclones, east coast lows or major troughs which may occur on sub-annual or decadal time scales. For many inland sites, recharge from such events results from widespread flooding over hundreds or thousands of kilometers, introducing an evaporated signature to the groundwater, or one that reflects a different composition to local rainfall. In contrast, reliable seasonal rainfall from the monsoon in the north, or winter rainfall in the south west leads to groundwater signatures in alluvial, karst and fractured rock aquifers that reflect wet season averages. A better understanding of how these processes vary across the continent improves our ability to apply stable isotopes to trace groundwater recharge and ultimately provides valuable information for water resource managers to understand the sustainability of groundwater and connected surface water systems. © Author(s) 2017. CC Attribution 3.0 License.
Authenticating genuine Kakadu plum (Terminalia ferdinandiana) powders from fakes using stable isotope analysis and elemental profiling
(Elsevier, 2024-08) Keaney, M; Mazumder, D; Tadros, CV; Crawford, J; Gadd, PS; Saeki, P; Sammut, J; Saintilan, N
Kakadu plum (Terminalia ferdinandiana) is a plant species endemic to northern Australia, attracting increasing consumer interest due to its multiple nutritional qualities. As a consumer product at a premium price point, the Kakadu plum may be susceptible to food fraud. This paper determines the prevalence of food fraud in the e-commerce Kakadu plum market. We applied stable isotope analysis (SIA) and elemental profiling using X-ray fluorescence (XRF) through Itrax to evaluate the authenticity of 13 commercially available Kakadu plum powdered samples purchased from Australian and overseas suppliers against four powdered samples directly provided by First Nations harvesters. Overseas and Australian-sourced powders were found to have distinct isotopic and elemental profiles. All overseas powders showed highly enriched δ13C values indicating they are fakes, not derived from Kakadu plum. Non-metric multi-dimensional scaling (nMDS) of elements also displayed distinct groupings between Australian-sourced and overseas powders, whilst analysis of similarity percentages (SIMPER) differentiated the elemental composition between groups. It was also observed that 89% of overseas products sold as Kakadu plum were deceptively labelled as other products. These results showed food fraud occurred along the supply chain of overseas-sourced product. Given the complexities of multi-national food systems, utilising a combination of stable isotopes and elemental profiling are straightforward applications for detecting fraudulent products. © 2024 Crown Copyright Published by Elsevier Ltd.
Baseline characterisation of source contributions to daily-integrated PM2.5 observations at Cape Grim using Radon-222
(Elsevier, 2018-08-20) Crawford, J; Chambers, SD; Cohen, DD; Williams, AG; Atanacio, AJ
We discuss 15 years (2000–2015) of daily-integrated PM2.5 samples from the Cape Grim Station. Ion beam analysis and positive matrix factorisation are used to identify six source-type fingerprints: fresh sea salt (57%); secondary sulfate (14%); smoke (13%); aged sea salt (12%); soil dust (2.4%); and industrial metals (1.5%). An existing hourly radon-only baseline selection technique is modified for use with the daily-integrated observations. Results were not significantly different for days on which >20 hours were below the baseline radon threshold compared with days when all 24 hours satisfied the baseline criteria. This relaxed daily baseline criteria increased the number of samples for analysis by almost a factor of two. Two radon baseline thresholds were tested: historic (100 mBq m−3), and revised (50 mBq m−3). Median aerosol concentrations were similar for both radon thresholds, but maximum values were higher for the 100 mBq m−3 threshold. Back trajectories indicated more interaction with southern Australia and the Antarctic coastline for air masses selected with the 100 mBq m−3 threshold. Radon-only baseline selection using the 50 mBq m−3 threshold was more selective of minimal terrestrial influence than a similar recent study using wind direction and back trajectories. The ratio of concentrations between terrestrial and baseline days for the primary sources soil, smoke and industrial metals was 3.4, 2.6, and 5.5, respectively. Seasonal cycles of soil dust had a summer maximum and winter minimum. Seasonal cycles of smoke were of similar amplitude for terrestrial and baseline events, but of completely different shape: peaking in autumn and spring for terrestrial events, compared to summer for baseline conditions. Seasonal cycles of industrial metals had a summer maximum and winter minimum. A significant fraction of the Cape Grim baseline smoke and industrial metal contributions appeared to be derived from long-term transport (>3 weeks since last terrestrial influence). Crown Copyright © 2018 Published by Elsevier Ltd.
Biotic, temporal and spatial variability of tritium concentrations in transpirate samples collected in the vicinity of a near-surface low-level nuclear waste disposal site and nearby research reactor
(Elsevier Science Ltd, 2011-06-01) Twining, JR; Hughes, CE; Harrison, JJ; Hankin, SI; Crawford, J; Johansen, MP; Dyer, LL
The results of a 21 month sampling program measuring tritium in tree transpirate with respect to local sources are reported. The aim was to assess the potential of tree transpirate to indicate the presence of sub-surface seepage plumes. Transpirate gathered from trees near low-level nuclear waste disposal trenches contained activity concentrations of (3)H that were significantly higher (up to similar to 700 Bq L(-1)) than local background levels (0-10 Bq L(-1)). The effects of the waste source declined rapidly with distance to be at background levels within 10s of metres. A research reactor 1.6 km south of the site contributed significant (p < 0.01) local fallout (3)H but its influence did not reach as far as the disposal trenches. The elevated (3)H levels in transpirate were, however, substantially lower than groundwater concentrations measured across the site (ranging from 0 to 91% with a median of 2%). Temporal patterns of tree transpirate (3)H, together with local meteorological observations, indicate that soil water within the active root zones comprised a mixture of seepage and rainfall infiltration. The degree of mixing was variable given that the soil water activity concentrations were heterogeneous at a scale equivalent to the effective rooting volume of the trees. In addition, water taken up by roots was not well mixed within the trees. Based on correlation modelling, net rainfall less evaporation (a surrogate for infiltration) over a period of from 2 to 3 weeks prior to sampling seems to be the optimum predictor of transpirate (3)H variability for any sampled tree at this site. The results demonstrate successful use of (3)H in transpirate from trees to indicate the presence and general extent of sub-surface contamination at a low-level nuclear waste site. Crown Copyright © 2011, Elsevier Ltd.
Calculated K, L, and M shell X-ray line intensities for light ion impact on selected targets from Z=6 to 100
(Australian Nuclear Science and Technology Organisation, 2011-09-01) Crawford, J; Cohen, DD; Doherty, G; Atanacio, AJ
A computer code to calculate the K, L, and M α, β and γ X-ray line intensities, KLMabgRatios, is described together with the input tables used to calculate these intensities for light ion bombardment of targets with atomic numbers from Z=6 to 100. The KLMabgRatios program was written with the main aim of updating the 1980’s data files used up till now (Clayton AAEC M113/1986), with more recent experimental and theoretical datasets published in the last 2 years or so. Preferred recommended K, L and M X-ray line intensities for light ion impact on selected targets for atomic numbers between Z=6 and 100 are given for 8 K lines, 17 L lines and 22 M lines as well as their corresponding ωK, ωL and ωM total shell fluorescence yields. In addition a program, wexplore, has been written to carry out Gaussian fits to experimental K, L and M X-ray spectra to better determine L and M X-ray production subshell cross sections for light ion bombardment. A section on the use of this wexplore program is also included in this report.
The canary or the coalmine? Isotopic evidence of drying climate versus groundwater outflow as the cause for recent losses from Thirlmere Lakes, NSW
(National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-24) Peterson, MA; Cendón, DI; Hughes, CE; Crawford, J; Hankin, SI; Krogh, M; Cowley, KL; Cohen, TJ; Andersen, MS; Anibas, C; Glamore, W; Chen, SY; Timms, W; McMillan, T
The Thirlmere Lakes Research Program (TLRP) is a collaboration investigating water loss mechanisms in recent drying of five adjacent lakes, located 75 km south-west of Sydney. Some stakeholders and previous studies have perceived a correlation with local longwall coal mining history and suspect deep fracture outflow. Others suggest the lakes are simply responding to a drier climate, serving as the canary in the broader climate-change ‘coal mine’. ANSTO has applied recurrent isotopic and chemical monitoring of the lakes and adjacent groundwater over two years to unravel some of the mystery of their recent water losses. Each lake behaved uniquely, but they shared some common trends. Steady enrichment of stable water isotopes, 2H and 18O, indicates the dominance of evaporation, with minimal losses to groundwater or through transpiration. Lake Cl/Br ratios were very low and clustered in three groups, two trending away from initial ratios indicative of groundwater input. 3H and 14C show recent rainfall and/or runoff as the main contributors to lake waters, with apparent ages in the adjacent shallow groundwater up to several decades. High levels of 222Rn from shallow bores suggest a close association between the peats enclosing the lakes and 238 U from ancient erosion, or proximity of an underlying shale lens. The only deep piezometer (72-84 m) near the lakes showed negligible contributions from the lakes or recent surface water. The trends in isotopic and chemical parameters infer that evaporation is sufficient to explain recent water losses from most of these perched lakes. Trends in some lakes hint that these had previous inputs from groundwater. While the historical variability of groundwater input to the lakes remains unknown, there is no current evidence of major losses to groundwater. Thirlmere Lakes will exist only intermittently under dry climate conditions. © The Authors
Changes in below‐cloud evaporation affect precipitation isotopes during five decades of warming across China
(American Geophysical Union, 2021-03-28) Wang, SJ; Jiao, R; Zhang, MJ; Crawford, J; Hughes, CE; Chen, FL
Based on daily meteorological records for 651 sites across China during the period 1960–2018, we estimated the changes in isotopic variations in raindrops as they descend from cloud base to ground over past decades, and tested the sensitivity of isotopic variations to climate parameters like air temperature and relative humidity. Air temperature correlates positively and relative humidity correlates negatively with below‐cloud isotopic variation. Generally, the below‐cloud evaporation effect on precipitation isotopes in the arid and semi‐arid regions of China is much greater than that in the humid and semi‐humid regions, although the impact might be reduced under cold‐arid or hot‐humid conditions. With aridity increasing with distance from the coast, the continental effect of precipitation isotopes is modified due to the below‐cloud evaporation. The seasonal pattern of the measured isotopic composition in precipitation near the ground and estimated at cloud base, is still similar in most regions, although the seasonal range is higher at the ground. During the last five decades, the below‐cloud evaporation effect has enhanced for the cold and arid regions of China especially across Qinghai‐Tibet Plateau and Inner Mongolia, due to combined effects of increasing air temperature and decreasing relative humidity. Although the below‐cloud evaporation effect is not always the dominant factor influencing the variability of stable isotopes, it needs to be considered as one of the contributing factors. This enhanced effect may impact the interpretation of past climate based on stable water isotopes, particularly in paleoclimate studies using speleothems and tree rings. © 2021. American Geophysical Union
Characterisation and source apportionment of fine particulate sources at Hanoi from 2001 to 2008
(Elsevier, 2010-01) Cohen, DD; Crawford, J; Stelcer, E; Bac, VT
PM2.5 particulate matter has been collected on Teflon filters every Sunday and Wednesday at Hanoi, Vietnam for nearly eight years from April 2001 to December 2008. These filters have been analysed for over 21 different chemical species from hydrogen to lead by ion beam analysis techniques. This is the first long term PM2.5 dataset for this region. The average PM2.5 mass for the study period was (54 ± 33) μg m―3, well above the current US EPA health goal of 15 μg m―3. The average PM2.5 composition was found to be (29 ± 8)% ammonium sulfate, (8.9 ± 3.3)% soil, (28 ± 11)% organic matter, (0.6 ± 1.4)% salt and (9.2 ± 2.8)% black carbon. The remaining missing mass (25%) was mainly nitrates and absorbed water. Positive matrix factorisation techniques identified the major source contributions to the fine mass as automobiles and transport (40 ± 10)%, windblown soil (3.4 ± 2)%, secondary sulfates (7.8 ± 10)%, smoke from biomass burning (13 ± 6)%, ferrous and cement industries (19 ± 8)%, and coal combustion (17 ± 7)% during the 8 year study period. © 2010, Elsevier Ltd.
Characterising diurnal & synoptic timescale changes in urban air quality using Radon-222
(Europenan Geosciences Union, 2020-05-01) Chambers, SD; Kikaj, D; Podstawczyńska, A; Williams, AG; Crawford, J; Griffiths, AD
Urban air quality is strongly influenced by the atmosphere’s ability to disperse primary emissions and opportunities for secondary pollution formation. In mid- to high-latitude regions that experience enduring winter snow cover or soil freezing, regional subsidence and stagnation associated with persistent anti-cyclonic conditions such as the “Siberian High” can lead to “cold pool” or “persistent inversion” events. These events can result in life-threatening pollution episodes that last for weeks. While often associated with complex topography [1,2], persistent inversion events can also influence the air quality of urban centres in flat, inland regions [3]. This presentation will describe a recently-developed radon-based technique for identifying and characterising synoptic-timescale persistent inversion events, which is proving to be a simple and economical alternative to contemporary meteorological approaches that require regular sonde profiles [1]. Furthermore, key assumptions of the radon-based technique to characterise diurnaltimescale changes in the atmospheric mixing state described by Chambers et al. [4] are violated during persistent inversion conditions. Here we demonstrate how atmospheric class-typing, through successive application of radon-based techniques for identifying synoptic- and diurnaltimescale changes in the atmospheric mixing state, improves understanding of atmospheric controls on urban air quality in non-summer months across the full diurnal cycle. This knowledge translates directly to statistically-robust techniques for assessing public exposure to pollution, and for evaluating the efficacy of pollution mitigation measures. Lastly, we show how atmospheric class-typing can be used to enhance the evaluation of chemical transport models. © Author(s) 2020
Characterising terrestrial influences on Antarctic air masses using Radon-222 measurements at King George Island
(European Geosciences Union, 2014-09-18) Chambers, SD; Hong, SB; Williams, AG; Crawford, J; Griffiths, AD; Park, SJ
We report on one year of high-precision direct hourly radon observations at King Sejong Station (King George Island) beginning in February 2013. Findings are compared with historic and ongoing radon measurements from other Antarctic sites. Monthly median concentrations reduced from 72 mBq m−3 in late-summer to 44 mBq m−3 in late winter and early spring. Monthly 10th percentiles, ranging from 29 to 49 mBq m−3, were typical of oceanic baseline values. Diurnal cycles were rarely evident and local influences were minor, consistent with regional radon flux estimates one tenth of the global average for ice-free land. The predominant fetch region for terrestrially influenced air masses was South America (47–53° S), with minor influences also attributed to aged Australian air masses and local sources. Plume dilution factors of 2.8–4.0 were estimated for the most terrestrially influenced (South American) air masses, and a seasonal cycle in terrestrial influence on tropospheric air descending at the pole was identified and characterised. © Author(s) 2014
Chemical characterisation and source identification of atmospheric aerosols in the Snowy Mountains, south-eastern Australia
(Elsevier, 2018-07-15) Tadros, CV; Crawford, J; Treble, PC; Baker, AA; Cohen, DD; Atanacio, AJ; Hankin, SI; Roach, R
Characterisation of atmospheric aerosols is of major importance for: climate, the hydrological cycle, human health and policymaking, biogeochemical and palaeo-climatological studies. In this study, the chemical composition and source apportionment of PM2.5 (particulate matter with aerodynamic diameters less than 2.5 μm) at Yarrangobilly, in the Snowy Mountains, SE Australia are examined and quantified. A new aerosol monitoring network was deployed in June 2013 and aerosol samples collected during the period July 2013 to July 2017 were analysed for 22 trace elements and black carbon by ion beam analysis techniques. Positive matrix factorisation and back trajectory analysis and trajectory clustering methods were employed for source apportionment and to isolate source areas and air mass travel pathways, respectively. This study identified the mean atmospheric PM2.5 mass concentration for the study period was (3.3 ± 2.5) μg m−3. It is shown that automobile (44.9 ± 0.8)%, secondary sulfate (21.4 ± 0.9)%, smoke (12.3 ± 0.6)%, soil (11.3 ± 0.5)% and aged sea salt (10.1 ± 0.4)% were the five PM2.5 source types, each with its own distinctive trends. The automobile and smoke sources were ascribed to a significant local influence from the road network and bushfire and hazard reduction burns, respectively. Long-range transport are the dominant sources for secondary sulfate from coal-fired power stations, windblown soil from the inland saline regions of the Lake Eyre and Murray-Darling Basins, and aged sea salt from the Southern Ocean to the remote alpine study site. The impact of recent climate change was recognised, as elevated smoke and windblown soil events correlated with drought and El Niño periods. Finally, the overall implications including potential aerosol derived proxies for interpreting palaeo-archives are discussed. To our knowledge, this is the first long-term detailed temporal and spatial characterisation of PM2.5 aerosols for the region and provides a crucial dataset for a range of multidisciplinary research. Crown Copyright © 2018 Published by Elsevier B.V.

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