Managing construction dust is primarily about mitigating the impact of works on stakeholders. The primary focus of dust monitoring is to identify any dust level increases, understand their cause, and take action to prevent or mitigate them. Visual observations and record keeping are usually the primary method of managing dust, supported by dust monitoring.
Many Construction Environmental Management Plans (CEMPs) have dust compliance rules in the form of time-based limits for PM2.5 and PM10 levels, typically covering days, weeks, months and/or years. The table below shows an example from Western Sydney Airport Bulk Earthworks (see references to NSW EPA & NEPM-AAQ below under Relevant Policy):
Compliance based measurements are typically required to undertaken using dust deposition gauges (DDGs), whereby samples after a period of time are sent to a lab to determine volume and type of dust over the previous period (usually a month). The obvious downside of dust deposit gauges is that any issues will only be identified weeks after they occurred.
It is much more useful to know in real-time whether a site might exceed the limit, as it allows action to be taken to prevent potential issues occuring. New technologies such as optical particle counters allow for this, along with calculating the daily values as often required. The SiteHive Hexanode uses an optical particle counter.
Real-time monitoring using this new technology allows management rules to be used throughout the day (e.g. rolling averages) to identify trends in the levels and enable remedial action before an event occurs.
The below shows an example of management rules from the Sydney Football Stadium redevelopment, and the full plan is linked here: Sydney Football Stadium:
Types of measurement
There are several ways to express the amount of particles in the air. Most State-based Governments (e.g. NSW EPA, QLD EPA) run air quality monitoring stations, using approved sampling methods: https://www.epa.nsw.gov.au/your-environment/air/industrial-emissions/sampling-analysing-air-emissions/approved-methods-sampling-analysing-air-pollutants to provide a network of air quality stations.
The methods used at these sites are TEOM (Tapered element oscillating microbalance), BAM (Beta attenuation monitoring ), or High/Low volume air samplers. All of these have filters that need maintaining/changing. These methods are very expensive and usually require permanent facilities. They are not typically used for construction monitoring.
SiteHive makes it really easy to access this data, by adding the nearest government reference station to each site for you, so you can compare ambient reference measurements with your onsite measurements.
The methods usually used for construction monitoring are outlined below, with reference grade stations being too large and expensive for these applications.
Dust Deposit Gauges (DDG)
Dust settles in a container over a defined period (usually 14 or 30 days) and is sent to a lab for analysis that usually provides reporting on volume, mass, and type of dust deposited.
The most commonly referred to method of dust sampling in the Australian and US standards is gravimetric sampling, which is a filter-based method. Gravimetric dust monitoring involves sampling a known volume of ambient air through a filter. The filters are sent to a lab to be weighed before and after exposure to determine the mass of particles. The collected dust sample is expressed as mass of dust (mg) per cubic meter (m3) of air.
Real-time monitoring differs from the other types of measurement in that it enables continuous and proactive monitoring of dust levels. It uses a variety of techniques (outlined below) that each have different price points and accuracy. The United States EPA has run a number of field tests with emerging sensors, showcasing their performance against reference grade monitors: US EPA Evaluation of Emerging Air Sensor Performance. It is these types of sensors that are more often used for real-time construction monitoring.
There are three types of light sensors generally used: a photometer, an optical particle counter and a Beta Attenuation Monitor (BAM). A photometer measures the “transparency” of the air; an optical particle counter provides a particle count (the actual number of particles in the air); and a BAM will output a mass concentration. Note that photometers and particle counters may also output mass concentrations, but in these devices they are calculated based on the device readings, not the actual raw readings. Commercial real-time monitoring devices may include a combination of light sensors.
$$$ Beta attenuation monitoring (BAM) is a widely used air monitoring technique employing the absorption of beta radiation by solid particles extracted from air flow. The main principle is based on a kind of Bouguer (Lambert–Beer) law: the amount by which the flow of beta radiation (electrons) is attenuated by a solid matter is exponentially dependent on its mass and not on any other feature (such as density, chemical composition or some optical or electrical properties) of this matter.
$$ Photometers (e.g., DustTrak, which also collects a gravimetric sample) measure light reflected at a specific angle, while nephelometers (e.g., pDR) measure light reflected over as wide a range of angles as possible. The DustTrak DRX is a combined photometer and optical counter, where a laser diode illuminates a sample stream and reflected light is directed onto a photodetector by a mirror. When properly calibrated the DustTrak DRX has <10% error in comparison to TEOM measurements (Wang et al., 2009).
$ Optical particle counters (e.g. Sensirion SPS30, Alphasense), measure the light scattered by individual particles carried in a sample air stream through a laser beam. These measurements are used to determine the particle size (related to the intensity of light scattered via a calibration based on Mie scattering theory) and particle number concentration. Particle mass loadings (PM1, PM2.5 and PM10) are then calculated from the particle size spectra and concentration data, assuming a particle density and refractive index (RI). The default settings (weighting index 2) for these parameters are typically: density = 1.65 g/ml and RI = 1.5+i0.
In the field, real-time monitors (e.g. optical particle counters) can be calibrated by co-locating instruments for a period of time, and by using a scaling factor (i.e., a calibration factor, sometimes called a K-Factor) or curve of best fit to adjust the measurements reported by the real-time monitors to match the gravimetric measurements. Typically to undertake this process portable low-volume air samplers are used to generate a K-Factor for cheaper, more portable devices such as optical particle counters.
Kaiterra knowledge base, explaining context and methodology for how they measure pm2.5.
The South Coast Air Quality Management District (South Coast AQMD) is the agency responsible for attaining state and federal clean air standards in the South Coast Air Basin in southern California. With a population of 14.6 million, the South Coast Air Basin covers an area of 6,745 square miles, which includes Los Angeles. In order to inform the public about the actual performance of commercially available ‘low-cost’ air quality sensors, the South Coast AQMD has established the Air Quality Sensor Performance Evaluation Center (AQ-SPEC) program, which characterises sensors under both field and laboratory conditions. AQ-SPEC field evaluations.
The standards in Australia are very specific to each method, and have not yet kept up with newer technology e.g. optical particle counters. If your management plan specifies a standard below that you need to comply with, then you must use that method. Where however no standard is defined, or the management plan is more focused on real-time management, then optical particle counters are a great tool for the job.
The National Environment Protection (Ambient Air Quality) Measure - NEPM aims to achieve National Environment Protection Standards as assessed in accordance with (set) monitoring protocol. The desired outcome of the NEPM is an ambient air quality that allows for the adequate protection of human health and well-being.
Each state also typically has their own approved sampling methods, which overlap with the NEPM, for example the NSW EPA approved methods for the sampling and analysis of air pollutants.
Queensland Government Environment department summary of methods for sampling particulates.
Standards referenced by the NEPM:
Particles as PM10
Determination of Suspended Particulate Matter-PM10 High Volume Sampler with Size Selective Inlet-Gravimetric Method AS/NZS 3580.9.6:2003
Determination of Suspended Particulate Matter- Dichotomous sampler (PM10, coarse PM and PM2.5) – Gravimetric method AS/NZS 3580.9.7:2009
Determination of Suspended Particulate Matter-PM10 continuous direct mass method using tapered element oscillating microbalance analyser. AS/NZS 3580.9.8-2008
Determination of Suspended Particulate Matter-PM10 Low Volume Sampler-Gravimetric Method AS/NZS 3580.9.9:2006
Determination of Suspended Particulate Matter-PM10 beta attenuation monitors AS/NZS 3580.9.11:2008/Amdt 1 :2009
Particles as PM2.5
Determination of Suspended Particulate Matter-PM2.5 low volume sampler-Gravimetric Method AS/NZS 3580.9.10:2008
Determination of Suspended Particulate Matter-PM2.5 beta attenuation monitors AS/NZS 3580.9.12:2013
Determination of Suspended Particulate Matter-PM2.5 continuous direct mass method using a tapered element oscillating microbalance monitor AS/NZS 3580.9.13:2013
Determination of Suspended Particulate Matter-PM2.5 high volume sampler with size selective inlet – Gravimetric Method AS/NZS 3580.9.14:2013
Glossary of terms
PM2.5 - Airborne particles less than 2.5 micrometres in diameter
PM10 - Airborne particles less than 10 micrometres in diameter
TSP - Airborne particles up to about 100 micrometres in diameter are referred to as TSP (total suspended particles).
TPS - Typical Particle Size, output from some optical laser particle counters
BAM - Beta Attenuation Monitor
TEOM - Tapered element oscillating microbalance