Janaka Gunawardena

Mathematical relationships for metal build-up on urban road surfaces based on traffic and land use characteristics

The study investigated the influence of traffic and land use parameters on metal build-up on urban road surfaces. Mathematical relationships were developed to predict metals originating from fuel combustion and vehicle wear. The analysis undertaken found that nickel and chromium originate from exhaust emissions, lead, copper and zinc from vehicle wear, cadmium from both exhaust and wear and manganese from geogenic sources. Land use does not demonstrate a clear pattern in relation to the metal build-up process, though its inherent characteristics such as traffic activities exert influence. The equation derived for fuel related metal load has high cross-validated coefficient of determination (Q(2)) and low Standard Error of Cross-Validation (SECV) values which indicates that the model is reliable, while the equation derived for wear-related metal load has low Q(2) and high SECV values suggesting its use only in preliminary investigations. Relative Prediction Error values for both equations are considered to be well within the error limits for a complex system such as an urban road surface. These equations will be beneficial for developing reliable stormwater treatment strategies in urban areas which specifically focus on mitigation of metal pollution.

Taxonomy of factors which influence heavy metal build-up on urban road surfaces

Heavy metals build-up on urban road surfaces is a complex process and influenced by a diverse range of factors. Although numerous research studies have been conducted in the area of heavy metals build-up, limited research has been undertaken to rank these factors in terms of their influence on the build-up process. This results in limitations in the identification of the most critical factor/s for accurately estimating heavy metal loads and for designing effective stormwater treatment measures. The research study undertook an in-depth analysis of the factors which influence heavy metals build-up based on data generated from a number of different geographical locations around the world. Traffic volume was found to be the highest ranked factor in terms of influencing heavy metals build-up while land use was ranked the second. Proximity to arterial roads, antecedent dry days and road surface roughness has a relatively lower ranking. Furthermore, the study outcomes advances the conceptual understanding of heavy metals build-up based on the finding that with increasing traffic volume, total heavy metal build-up load increases while the variability decreases. The outcomes from this research study are expected to contribute to more accurate estimation of heavy metals build-up loads leading to more effective stormwater treatment design.

Influence of traffic characteristics on polycyclic aromatic hydrocarbon build-up on urban road surfaces

Traffic is one of the prominent sources of polycyclic aromatic hydrocarbons (PAHs), and road surfaces are the most critical platform for stormwater pollution. Build-up of pollutants on road surfaces was the focus of this research study. The study found that PAHs build-up on road surfaces primarily originate from traffic activities, specifically gasoline powered vehicles. Other sources such as diesel vehicles, industrial oil combustion and incineration were also found to contribute to the PAH build-up. Additionally, the study explored the linkages between concentrations of PAHs and traffic characteristics such as traffic volume, vehicle mix and traffic flow. While traffic congestion was found to be positively correlated with 6-ring and 5-ring PAHs in road build-up, it was negatively correlated with 3-ring and 4 ring PAHs. The absence of positive correlation between 3-ring and 4-ring PAHs and traffic parameters is attributed to the propensity of these relatively volatile PAHs to undergo re-suspension and evaporation. The outcomes of this study are expected to contribute to effective transport and land use planning for the prevention of PAH pollution in the urban environment.

Characterisation of atmospheric deposited particles during a dust storm in urban areas of Eastern Australia

The characteristics of dust particles deposited during the 2009 dust storm in the Gold Coast and Brisbane regions of Australia are discussed in this paper. The study outcomes provide important knowledge in relation to the potential impacts of dust storm related pollution on ecosystem health in the context that the frequency of dust storms is predicted to increase due to anthropogenic desert surface modifications and climate change impacts. The investigated dust storm contributed a large fraction of fine particles to the environment with an increased amount of total suspended solids, compared to dry deposition under ambient conditions. Although the dust storm passed over forested areas, the organic carbon content in the dust was relatively low. The primary metals present in the dust storm deposition were aluminium, iron and manganese, which are common soil minerals in Australia. The dust storm deposition did not contain significant loads of nickel, cadmium, copper and lead, which are commonly present in the urban environment. Furthermore, the comparison between the ambient and dust storm chromium and zinc loads suggested that these metals were contributed to the dust storm by local anthropogenic sources. The potential ecosystem health impacts of the 2009 dust storm include, increased fine solids deposition on ground surfaces resulting in an enhanced capacity to adsorb toxic pollutants as well as increased aluminium, iron and manganese loads. In contrast, the ecosystem health impacts related to organic carbon and other metals from dust storm atmospheric deposition are not considered to be significant.

Influence of traffic and land use on urban stormwater quality

Urbanisation is a common phenomenon in most parts of the world as a result of increasing numbers of people moving into urban areas. This results in the increased use of motor vehicles and demand for living areas. The use of motor vehicles and other anthropogenic activities common to urban areas introduce a wide range of pollutants to the urban environment, including toxic species such as heavy metals and polycyclic aromatic hydrocarbons (PAHs). These pollutants are either directly deposited on ground surfaces such as roads or initially accumulate in the atmosphere and subsequently deposited on ground surfaces. When rainfall occurs, the deposited pollutants can be washed off by stormwater runoff and transported to receiving water bodies, undermining the urban water environment. In order to mitigate stormwater pollution, a diversity of treatment devices are employed and their effective design is dependent on an in-depth understanding of pollutant processes and pathways. Additionally, state-of-the-art knowledge is also required for the development of effective stormwater management strategies to minimise the adverse impacts on receiving water bodies due to urbanisation. This book focuses on three important pollutant processes and transport pathways, namely, atmospheric build-up, atmospheric deposition (including dry and wet deposition) and build-up on road surfaces. Heavy metals and PAHs were the primary pollutants investigated in this study. Since traffic and land use are considered as the primary influential factors in pollutant generation, this research study selected a total of 15 study sites with varying traffic and land use characteristics in the Gold Coast, Queensland State, Australia. Three types of samples were collected at the selected study sites. These included atmospheric samples, atmospheric dry and wet deposition samples and road build-up samples. Univariate and multivariate data analysis techniques and mathematical modelling approaches were employed for the investigations undertaken and to create knowledge relating to the relationship between pollutants, traffic and land use, and for defining the linkages between pollutants in the atmospheric and ground phases. It was noted that the concentrations of heavy metals and PAHs in the atmospheric phase are higher during weekdays when compared to weekends due to higher traffic volume on weekdays. Therefore, this could lead to increased human health risk during weekdays. Additionally, Zn was found to be the most abundant heavy metal species in the atmosphere, atmospheric (wet and dry) deposition and road build-up. This suggests that the presence of Zn in road stormwater runoff merits particular attention, compared to other heavy metal species. Light molecular weight PAHs (3–4 rings) showed higher concentrations and spatial variability compared to heavy molecular weight PAH species (5–6 rings) in both, atmospheric phase and road build-up. This is attributed to the volatile nature of light molecular weight PAHs. Heavy duty vehicle traffic volume is the primary source of PAHs and industrial land use tends to produce higher loads of PAHs than commercial and residential land uses. These outcomes demonstrate the important role atmospheric pollutants play in contributing to road stormwater pollution through atmospheric deposition. Furthermore, a modelling approach was developed to estimate the annual loads of traffic-related pollutants in stormwater runoff from a given road site by incorporating a series of replication equations to a widely used computer model tool. Pollutant loads were modelled by assigning co-fraction coefficients of solids. The modelling approach developed can be used not only to estimate solids generation from road sites, but also as a planning tool to identify the enhancements required to improve urban stormwater quality.

Primary Traffic Related Pollutants and Urban Stormwater Quality

Urbanisation introduces a range of pollutants to the urban environment. These pollutants include many toxic species. They are primarily sourced from traffic and land use related activities. The pollutants are directly deposited on ground surfaces or initially emitted to the atmosphere and subsequently deposited on ground surfaces via depositional processes. These pollutants are removed by stormwater runoff and transported to receiving water bodies, undermining the urban water environment. This chapter discusses the primary traffic related pollutants and their transport pathways. Pollutants discussed include solids, heavy metals, polycyclic aromatic hydrocarbons and airborne particulate pollutants while their transport pathways include atmospheric build-up, dry and wet deposition, build-up and wash-off on road surfaces.

Implications for Engineered Applications and Recommendations for Future Research Directions

This chapter provides a consolidated summary of the outcomes from the research study undertaken to investigate the influence of traffic and land use on pollutant processes as well as the practical application of the study findings. The chapter also discusses key areas where currently, there are significant knowledge gaps and further investigations are warranted. These include, the assessment of ecological and human health risks posed by stormwater pollutants, the investigation of other traffic related pollutants and the understanding of the adsorption mechanisms of pollutants—solids inherent in the different transport pathways.

Influence of Traffic and Land Use on Pollutant Transport Pathways

This chapter discusses the influence of traffic and land use factors on atmospheric pollutants build-up, dry and wet deposition and build-up on urban surfaces. Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) were the focus of discussion in this chapter as these pollutants are ubiquitous in the urban environment, being commonly associated with traffic and anthropogenic activities common to urban areas and are toxic to human and ecosystem health. The research outcomes presented in this chapter confirm the influential role played by atmospheric pollution in stormwater pollution. The study outcomes also highlight the linkage between pollutants species with their potential sources and influential factors. Furthermore, the linkages between pollutants in the atmospheric phase, depositions and build-up on urban surfaces are also identified. For example, Zn was found to be the most abundant heavy metal element present in atmospheric build-up, atmospheric deposition and build-up on road surfaces, whilst light molecular weight PAHs have a higher concentration and spatial variability in both, atmospheric and road surface phases. The analysis also highlighted the influence exerted by heavy duty vehicle traffic on pollution in the urban environment, particularly in industrial land use areas. The knowledge created will contribute to informed decision making for minimising urban stormwater pollution and thereby safeguarding the urban water environment. In addition, these outcomes can also be applied in urban transport planning in order to enhance urban liveability.

Predicting Stormwater Quality Resulting from Traffic Generated Pollutants

Accurate stormwater quality prediction is essential for effective stormwater quality mitigation. The knowledge created in the previous chapters was applied for predicting stormwater quality using mathematical models. This chapter presents a detailed discussion of the outcomes of the modelling study including model selection, input parameter determination and model setup. The model setup procedure consisted of model schematisation, determination of boundary conditions and replication of pollutants build-up and wash-off processes. Eventually, the estimation results using the modelling approach developed are given and a series of predictive equations based on traffic and land use characteristics were developed. These outcomes are expected to contribute to the translation of research outcomes into practical recommendations for model developers, decision-makers and stormwater treatment system designers.

Heavy metals transport pathways: The importance of atmospheric pollution contributing to stormwater pollution

Pollution has become a serious issue in the urban water environment as stormwater runoff transports a range of pollutants to receiving water bodies, undermining water quality and posing human and ecosystem health risks. Commonly, the primary focus of stormwater quality research is on the role of pollutants directly accumulating at the ground phase. However, atmospheric phase can also exert a significant impact on stormwater quality through atmospheric deposition. Unfortunately, only limited research has focused on the linkage between atmospheric and ground phases in relation to urban stormwater quality. The study discussed in this paper characterised the four primary transport pathways, atmospheric build-up (AB), atmospheric deposition (AD) and road surface build-up (BU) and wash-off (WO) in relation to heavy metals, which is a key urban stormwater pollutant. The research outcomes confirmed the direct linkage between atmospheric phase and ground phase and in turn the significance of atmospheric heavy metals as a contributing source to stormwater runoff pollution. Zn was the most dominant heavy metal in all four pathways. For the AB pathway, atmospheric heavy metal pollution on weekdays is more serious than weekends. For the AD pathway, dry atmospheric deposition of heavy metals is positively correlated to dry days, whilst wet (bulk) deposition is related to rainfall depth. For the BU pathway, heavy-duty vehicle traffic volume was found to be the most important source. For the WO pathway, industrial and commercial areas tend to produce higher heavy metal concentrations in stormwater runoff than residential areas. The study results will contribute to the creation of effective urban stormwater pollution mitigation strategies and thereby enhancing the quality of the urban water environment.