Dust is a general term used to describe microscopic solid particles suspended in the air.
It is well recognised nationally and internationally that the most common metrics for measuring air quality is particulate matter (PM), specifically PM10 and PM2.5. This refers to the size in aerodynamic diameter measured in micrometres (μm).
The composition of dust can vary from location to location. In cities dust tends to be dominated by small particles from combustions sources, such as vehicle emissions. In regional areas, combustions sources are less concentrated, and dust tends to be dominated by larger particles. In Port Hedland, the composition of dust is significantly different, consisting largely of iron oxide.
The air quality is regulated by the WA Department of Water and Environmental Regulation (DEWR) under the Environmental Protection Act 1986 (WA).
DWER establishes the requirements for individual operators to manage, monitor and report on dust levels in accordance with licence conditions. All operators implement a range of dust mitigation measures which vary depending on specific licence conditions to ensure legal requirements are met.
PHIC established the Port Hedland Ambient Air Quality Monitoring Network (the Monitoring Network) in 2010 to closely monitor the overall air quality in Port Hedland.
Individual companies operate under a Part V environmental licence as part of the Environmental Protection Act, which sets out requirements to manage, monitor and report dust levels within the boundaries of their individual operations.
PHIC partner companies are committed to implementing leading fit-for-purpose dust mitigation and management practices.
A range of factors can be sources dust in Port Hedland such as:
- Ambient dust levels due to the nature of the semi-arid environment.
- Port activities – bulk material storage and handling.
- Other industrial activities – scrap metal processing, sand blasting, metal fabrication.
- Bushfires, pollen, sea spray.
- Dust storms.
Meteorological conditions play a significant role in the dispersion and generation of dust emissions in and around the town of Port Hedland.
The Pilbara region is an arid environment experiencing subtropical climatic conditions. Dry conditions and strong winds will result in a higher level of dust emissions from both industry and natural sources.
The dust emissions will also have a greater radius of impact during periods of stronger wind speeds due to dust remaining suspended in the air for longer periods and therefore being carried further distances.
The prevailing wind conditions during the wet and dry seasons of northern Australia can be variable.
The variability in the wind speed and wind direction in Port Hedland will result in variation of dust emissions and in the areas potentially affected by dust.
Wet conditions assist in the suppression of dust.
The direction of the wind determines where particulates in the atmosphere will travel. Another factor that influences particulates is the wind speed – low wind speeds reduce dispersion which can result in increasing concentrations of particulates while high wind speeds, which can increase the rate of dispersion, also results in wind erosion from open areas such the spoil bank.
Unseasonal or unusual wind patterns can impact can result in a variation to average seasonal dust outcomes. The classic example are the iconic dust storms that occur in the Pilbara when air from the base of a storm pushes dust upwards creating a wall of dust.
The guideline of 70µg/m3 PM10 (24-hour average) was established in Port Hedland based on the WA Department of Health 2016 Health Risk Assessment and the advice of the Port Hedland Dust Management Taskforce.
The National Environmental Protection Measure (NEPM) standards for Ambient Air Quality are based on an urban environment. It is important to note the composition of dust from Port Hedland is significantly different to that found in urban environments.
Dust in urban environments typically consists of particulate matter from combustion sources such as road traffic.
The Network was established by PHIC as a recommendation of the Porth Hedland Dust Management Taskforce (2010 Report).
Since then, the Network has provided data and informed the work of the Taskforce and the Health Risk Assessment, has assisted industry in the development of strategies and evaluation of dust impacts from the Port of Port Hedland.
It has also assisted industry in the continuous improvement of its performance on dust emissions.
Industry has been undertaken and invested heavily in the implementation of substantial dust mitigation activities for more than 10 years.
This has resulted in dust readings initially falling and then remaining steady, while throughput at the Port has tripled.
Industry recognises it contributes to dust in Port Hedland, but it is not the only source of dust in what is a semi-arid environment.
There are many contributing factors to dust in Port Hedland, including natural bushfires, port activities, light industrial areas, urban activities and prevailing wind patterns.
Not all of these can be controlled by industry. Nevertheless, industry is committed to implementing leading dust suppression methods and will continue to do this.
The clear intent of the State Government’s response to the 2016 Port Hedland Dust Management Taskforce Report- released in October 2018 – was that while air quality guidelines and dust management activities are an appropriate response to managing dust emissions, other non-regulatory measures were also required including town planning amendments, town greening initiatives and more health education.
PHIC will continue to fund the ongoing operations of the Monitoring Network following its transfer to DEWR under a cost recovery arrangement.
The establishment and ongoing operation of the Port Hedland Ambient Air Quality Monitoring Network (the Network) was a key initiative of PHIC.
The Network has provided data and informed the development of strategies and evaluation of dust impacts from the Port of Port Hedland and has assisted industry to continuously improve its performance on dust emissions.
The transitioning the Network to the regulator was once of the recommendations of the Taskforce.
In line with that recommendation, PHIC is currently working with the Department of Water and Environmental Regulation (DWER) to transition the management of the Network to the regulator.
The transition to DWER is expected to take several months to complete.
As an industry group, PHIC and its members, bring substantial expertise in terms of dust mitigation and environmental knowledge.
Recognising this, a steering committee comprised of representatives of PHIC’s dust working group DWER staff, has been established to guide the transition.
LiDAR – Light Detection and Ranging – was developed in the early 1960s and has proven to be an extremely versatile technology used for a wide variety of purposes including remote sensing, vehicle automation and atmospheric studies.
The instrument (transmitter) releases rapid pulses of laser light along a path (to a receiver) and measures the time it takes for each light pulse to return. This is a similar principle to radar, except it uses a laser beam. The laser pulse signal strength is reduced as it reflects on larger particles in the atmosphere, such as pollen, water droplets, dust etc. The light that is not reflected by particles continues.
In the case of Port Hedland, the atmospheric LiDAR studies were seeking to understand the potential source, directional movement of dust plumes and concentrations of dust particles in the Port Hedland Airshed.
LiDAR measures the relative concentration of all particulate matter (not just dust) including PM10 and PM2.5, water vapour, and other suspended particulates and solid objects, which can then be represented visually.
LiDAR is a useful tool in this regard. However care should be exercised when interpreting such imagery because LiDAR does not differentiate between particulates and solid objects.
LiDAR only operates at the level it has been set.
In most atmospheric LiDAR studies there is a requirement to validate the intensity of the return pulse through using measured data from secondary monitoring systems to develop a relationship between what the LiDAR has measured against the results from more traditional monitoring methods. However, the assumption that LiDAR is measuring only PM10 concentration is not correct.
A LiDAR can only map the extent and location of a dust plume in relative terms in real-time and it is recognised as a practical measurement technique to allow for two or in some cases three-dimensional mapping of a plume.
DWER said its 2017 study helped identify the location of dust sources and the movement of dust plumes in the Port Hedland airshed. It was not intended to demonstrate LiDAR’s use as a regulatory tool because of limitations with current forms of the technology.
No. LiDAR measures all particulate matter in the atmosphere. It does not differentiate between types of particulate matter including dust (PM10, PM2.5), water vapour, and other suspended particulates and solid objects. When the LiDAR beam intersects with infrastructure (buildings, equipment) at the elevation plane of the LiDAR monitor, the heat map appears as red and could be interpreted as dust particles. That is, the visual representation is not accurate and can easily be misread. The same could apply during period of rain when the LiDAR pulse if reflected by water droplets.
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