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This paper describes an investigation into fugitive dust patterns and characteristics at a 200 hectare oil and gas terminal in the Middle East. Dust monitoring took place as part of an environmental and socio-economic impact assessment (ESIA) for proposed construction work, with initial monitoring over three months as part of a baseline study. Once the new phase of construction had started, passive dust monitoring was undertaken for 18 months using an extensive array of sticky pad dust collectors, with samples of dust in directional flux and deposited dust obtained. Dust monitors were placed upwind and downwind of the construction site, near building activities, and adjacent to nearby receptors. Collected dust samples were subjected to basic analysis for dust coverage (AAC %) and dust soiling (EAC %) with further samples later chosen for additional elemental, mineralogical and particle size analysis. Dust was removed from the sticky pads so that elemental analysis could be undertaken using ICP-MS and mineralogical analysis could be completed using SEM-EDX. Particle size analysis was accomplished using laser granulometry. Dust composition was compared with reference to background dust and soils. Results showed that collected dusts, both from the baseline study and construction phase and from background samples and receptors, were comprised of similar major minerals (r2 values > 0.78) to the calcareous sandy silts and clays that make up the majority of local soils. Similar results (r2 > 0.79) were also found for proportions of major elements in background dusts, receptor-collected dusts, and soils. One notable exception to the findings of dust homogeneity was the increased presence of calcite (and thus Ca) in samples near to roads: this is thought to originate from road traffic spillages of limestone which is quarried nearby. Particle size distributions for dust samples were also similar across samples at individual monitoring periods, but seemed to vary temporally in response to differing weather conditions. Weather data from an onsite monitoring station were also collected throughout the study and temporal dust levels were investigated in relation to individual weather factors. High dust levels originating from north of the site were recorded throughout the study period, and were observed to correlate with respective high winds from the north. Dust levels were also significantly increased during summer months and after periods of low rainfall. A predictive model for background dust propagation was therefore developed midway through the study, using wind strength and frequency from the north, temperature, and antecedent rainfall. Background dusts were defined as those arriving from north of the site (330° - 30°) and collected at dust monitors unaffected by construction workings. Linear regression was used to incorporate the different weather parameters into individual weather factors which combined to create a prediction of background dust levels. The resulting model, based on the first year of data, was subsequently tested against recorded levels over the next six months with high levels of accuracy observed (r2 > 0.78). The model was also tested against data collected during the baseline study with further positive results (r2 > 0.67).

Fugitive dust from industrial activities is a long-standing and intractable problem. Quarrying and mining, construction and demolition, landfill, waste transfer and reprocessing, bulk materials handling (especially at ports, docks and harbours), and arable farming are obvious examples where dust is inevitably produced. The impacts of dust emissions from such activities are broadly recognised but, especially within crowded urban and suburban areas where industry and residential areas are often juxtaposed, there may be many potential dust sources within and beyond any given locality. Consideration of potential fugitive dust impacts from planned industrial sites is a frequent part of environmental and social impact assessment, and subsequent monitoring of dust emissions a necessary test enforced by legislation and/or best practice guidance. Rarely, but in such cases significantly, disputes may arise about the causes and consequences of dust impacts. These can become good examples for environmental forensics, requiring the constraint of source - pathway - receptor with sufficient robust evidence for responsibilities to be established and decisions to be made. Recent developments in passive (unpowered) dust monitoring utilising ‘sticky pad’ samplers (Datson et al., 2011; 2012) have facilitated the monitoring of dust in flux on the pathway between source and receptor, and in deposition at the receptor. When combined with established procedures for elemental analysis (Fowler et al., 2010), source attribution studies become possible. This contribution describes two examples of such work which have been undertaken on behalf of the UK Environment Agency (EA), one related to hazardous waste disposal at a rural landfill site, the other to varied industrial activity in an urban setting. Both studies follow the same overall rationale and use DustScan® monitoring equipment and methods. Briefly, after careful consideration of site circumstances and potential dust sources, directional and/or deposited dust gauges are located between the site and potential receptor(s), and at ‘proxy’ receptor locations. Where possible, an upwind location is included, to help establish the local background dust abundance and character. Guided by the directional dust monitoring data (dust abundance by direction as AAC (absolute area coverage) and/or EAC (effective area coverage)), sub-samples are excised from “arcs of interest” on the sticky pads – each representing the direction that connects source and receptor, to a 15˚ resolution. Sub-samples are also taken from sticky pads used to capture dust in deposition, according to an appropriate and similar logic. These are then subjected to a range of laboratory analyses depending on purpose (and finance), ranging from light and scanning electron microscopy, gravimetry and granulometry, to elemental analysis by ICPAES or ICP-MS. Elemental data form the basis of source attribution, either by judgemental establishment of dust differences based on knowledge of potential source(s), or - if the data set is appropriate - by multivariate statistics and/or chemical mass balance procedures. The first case study (hazardous waste landfill) was commissioned as part of the planning application process for renewal of the site licence. It demonstrates that with sufficient prior knowledge and comparatively simple site circumstances, it is possible to make confident apportionment conclusions based on relatively few samples. The second study reflects work in progress at a more complex site involving several industrial processes, including waste transfer, metals recycling, roadstone coating and waste incineration. It shows that, again with a modest number of samples, sensible constraints can be placed on the potential origin of fugitive dusts and their dispersal into the local environment.

DustScan is a passive (i.e. unpowered) dust sampling method. It uses a transparent adhesive ‘sticky pad’ to sample dust in flux and in deposition for subsequent image-based quantification and, as appropriate, geochemical analysis. Samples are obtained over typically 7 – 14 day intervals in the vicinity of industrial sites such as quarries, surface coal mines, landfill sites and construction and demolition sites. DustScan was developed at the University of Leeds (Farnfield and Birch, 1997) and refined at DustScan Ltd and the University of Leeds (Datson and Birch, 2006). Dedicated geochemical analysis methods of DustScan samples using ICP-AES and ICP-MS have been developed (Datson and Fowler, 2007) and their use in environmental forensics has been demonstrated by quantifying dust propagation at a hazardous waste landfill site (Fowler et al. 2010). However, wider environmental forensic applications of the method have been constrained largely by the impracticality of detaching the sampled dust from the collection media. Until recently, the sticky pads have been die-cut from sheets of a proprietory transparent PVC film with a permanent, cross-linked polymer-acrylic adhesive. Whilst this type of adhesive has excellent environmental dust sampling characteristics, its formulation renders it essentially insoluble (except in solvents that also dissolve much of the dust, e.g. HF). Furthermore, on retrieval after field sampling the sticky pads are sealed with a transparent film to facilitate handling and minimise contamination, thus making physical removal of dust at a later date difficult. Since the most effective means of dust ‘extraction’ from the sticky pads has been in solution and the image-based quantification method does not assess dust mass, geochemical data have been reported in terms of concentration in the extraction (e.g. ppm in solution) rather than in the dust (e.g. mg g-1). Confidence in adequately low detection limits has also been compromised by variable concentrations of some metals (e.g. Zn, Ba) in the sampling media. Funding was obtained from the Finance South East Ltd (FSE) proof of concept (PoCKeT) fund to investigate alternative dust sampling media and, initially, to improve the elemental coverage and method detection limits. The project was carried out in conjunction between DustScan Ltd and the School of Earth and Environmental Sciences (SEES) at the University of Portsmouth. The new adhesive has similar transparency, tack and UV-resistance to the original but can be dissolved in an appropriate solvent. The new design has been tested in the field at a range of UK industrial sites as well as in a comprehensive bench testing programme. In the field trials, the new sampling media performed well in relation to the original sticky pads. Dust capture and retention were apparently similar and sample handling and processing for image analysis were satisfactory, although transparency was marginally less uniform. In the bench tests, both types of sticky pad were exposed to a known dust at different concentrations and wind speeds in an environmental wind tunnel. Correspondence between the sample media types was good to excellent in relation to the different image quantification methods applied. In addition, an array of elemental analysis tests was performed. NIST standard reference materials were applied to the new sticky pads, then extracted by dissolution of the adhesive and filtration onto 25 mm PTFE filter circles for ICP-MS analysis. Bulk dusts from a number of industrial sources were similarly applied, and analysed before and after application. An unanticipated benefit of the investigation has been the development of a practicable method to determine sampled dust mass in passive directional and deposited environmental dust samples, which has enabled reporting of mass/mass element concentrations in the dust samples after ICP-MS analysis.