Dust and sand storm monitoring

ECOTECH AUSTRALIA

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Background

The frequency and intensity of dust and sand storms in many parts of the world are steadily increasing due to droughts and climate change. The severity of such storms is anticipated to increase over the coming years.

These dust storms may last hours or days and cause huge damage and imposed a heavy toll on society with its physical effects, such as visibility reduction, heavy winds, red sky, hailstone and severe lightning.

Such Dust storms, have a negative impact on human health, and industrial products and activities. They reduce visibility, layer on skin and cloths, infiltrate buildings and find their way into food and drinking water leaving a permanent sandy feeling in your mouth.

Traditional dust monitoring instruments whether they be purely filter based gravimetric samplers or continuous monitors utilising Tapered Element Oscillating Microbalance (TEOM) or Beta Attenuation (BAM) simply are unable to cope with the high dust loads created by these storms. The filters on these instruments are quickly clogged and no further measurements are possible until a service technician visits to replace filters and filter tapes. In dust storm events this is impossible.

Therefore, over the past few years a need for alternate technology which are non filter based, can cope with extremely high dust loads, require minimal maintenance and can operate off solar power has been employed in regions such as the Gobi Desert of China for the continuous monitoring of dust storm events.

These instruments have demonstrated that an instrument can measure dust storm events with maintenance performed only once every 12 months. That it is possible to communicate remotely and that these systems can not only provide an early warning for dust events but have the accuracy and sensitivity to be an extremely useful tool in gauging hourly changes of visibility.

Infact such instruments have been utilised by a number of EPAs around the world, including all Australian EPAs for the purpose of measuring ambient visibility as well as providing an accurate indication of rising dust events.

Instrumentation

Aurora 1000 Integrating Nephelometer

The Aurora 1000 integrating nephelometer is designed to measure ambient particulates which impact directly on visibility.

Overview

Integrating nephelometers directly measure the light scattered by particles in an enclosed sample volume. The sampling chamber and light source are confined to a small volume so that the instrument makes a “point” or localised measurement of scattering. If the detector is placed parallel to the incident photons, only those photons that are scattered will be detected. The scattered radiation is integrated over a large range of scattering angles (forward, side and back directions) in a defined band of visible wavelengths. Since the total light scattered out of a path is the same as the reduction of light along a path due to scattering, the integrating nephelometer gives a direct estimate of bscat. bscat is an extremely good measure of ambient visibility and has been demonstrated to have a strong correlation with particulate concentrations.

The Aurora 1000 uses an extremely long life LED light source which emits at 525nm the Aurora 1000 measures the visual spectra which correlates most closely to human eyesight, providing the best possible measure of ambient visibility.

The Aurora Nephelometers provide many advantages when measuring both high and low particulate concentrations in extremely harsh environments these include:

Long life LED with an anticipated lifetime of over 5 years
525nm LED light source closely approximatess human visual range
Extremely large dynamic visual range from 10 m to 200 km
Large internal measurement cell preventing blockage of sampling surfaces
Low level of maintenance, typical a zero filter change every 6 months and cleaning of measurement cell every 12 months
Easily cleaned measurement cell
15 watt power requirements making it suitable for use with solar panels, eliminating the need for mains power
Internal sample heater controlled by a RH sensors eliminates effects due to fog.
Wide operating temperature range from -10 to 60 deg C eliminating the need for air conditioned enclosures
Remote communication over 3G, NextG, radio, satellite communication media for remote communication
Demonstrated correlation with PM2.5 U.S. Federal Equivalent Methods
Meets Australian standard AS/NZS 3580.12.1:2001 Determination of Light Scattering – Integrating Nephelometer Method

Calibration - click on slide bar for more details

Calibration

The Aurora 1000 Nephelometer is without a doubt the easiest instrument to calibrate for measurement of ambient visibility and particulate concentrations.

Zero Calibration

The Aurora includes an internal zero air filter designed to supply the measurement cell with air free of particulates and aerosols thus enabling an automatic zero calibration to be performed at any time with ease.

Span Calibration

Due to the measurement nature of an integrating nephelometer measuring the scattering coefficient of aerosols, any gas such as 100% CO2 or FM200 can be used to perform a span calibration of the instrument. Through the use of automatic internal span valves, a routine daily or weekly calibration can be configured in order to check the performance of the instrument. These calibrations can be set to occur automatically or triggered remotely if desired.

Light Source - click on slide bar for more information

Light Source

The light source used in the Aurora nephelometer is a patented LED opal glass light source which was designed for the Aurora range of nephelometers as it achieves a lambertian distribution as close as possible to ideal (light intensity is the same in every direction). With rapid improvements in LED technology, it has been possible to obtain higher intensity outputs from smaller LED packages and as such, the lightsource has just 3 LEDs for each wavelength. It is preferable over the older flash lamp technology for several reasons:

LED light sources generate a fraction of the heat generated by halogen flash lamps. This is a critical element when considering the impact that temperature and humidity can have on hygroscopic aerosols.

The LED light source is extremely robust, reliable and has been demonstrated to last well inexcess of 5 years without replacement. Halogen lamps are recommended for replacement every 6 months. Considering the remote location of some integrating nephelometers, this reduction in maintenance is very significant.

The LED array also eliminates the need for narrow bandpass optical filters due to the LEDs intrinsic wavelength selectivity.

These enhancements in nephelometer technology have improved the reliability, intensity and consistency of the light and thus the stability and performance of the instrument.

Humidity Control - click on slide bar for more information

Integral Humidity Control System

Ambient humidity has a significant effect on the scattering effects of hygroscopic particles. Typically, the higher the humidity, the greater the scattering effect. Radiative forcing data needs to be compared at the ambient humidity levels, however in order to compare the scattering effect of aerosols globally, GAW recommends that the relative humidity is less than 40%.

Climate change modelling rely upon the aerosol asymmetry parameter, but most assume it to be 0.7. Aerosol source, seasonal variation and changes in relative humidity influence the number, size and shape of aerosols and therefore affect the aerosol asymmetry parameter (Ogren, 2006). For instance a change of RH between 40% to 85% will influence this parameter by up to 20%.

Integrated Package - click on slide bar for more information

Robust Fully Integrated Monitoring Package

The Aurora series provides a fully integrated package that includes measurement system, sample pump, calibration valves, data logger and sample inlet heater in a compact low power instrument. The use of LEDs in the light source has significantly reduced the power demand of this instrument to less than 15 watts without heater and to no more than 60 watts with the heater fully active. The instrument was designed to be easily installed and operated.

haze monitoring nephelometer

The instrument was designed to be extremely robust, not require air conditioning and be capable of experiencing high altitudes without interfering with its operation. It has worked successfully in ambient temperatures as high as 50 deg C and as low as -20 deg C. It has withstood pressures experienced at altitudes of 10,000 m and continues to operate in traffic tunnels when exposed to a very high level of diesel particulates.

It can be operated unattended for long periods of time with its automatic calibration system and can have its data easily downloaded using Ecotech’s remote communication, validation and reporting software. The calibration is very straight forward, with internal span and zero valves allowing calibration gas and zero air to pass into the cell for calibration, all of which can be setup in the menu system

These features will enable the integrating nephelometer to be installed and reliably operated in a greater number of locations and in more inhospitable locations around the earth, providing information from these regions not previously available to researchers

Specifications - click on slide or more information

Specifications - Aurora 1000 integrating nephelometer

Range:

LDL:

Intensity function:

Temperature range:

Sample flow rate:

Weight:

Dimensions:

Power:

0 to >20 000 Mm^-1(equivalent 0.02 - 200 km)

0.3 Mm^-1 (equiv. 0.003 km (60 second averaged data)

9-170°

-20 to 50^oC

5 l/min approx

11.2 kg

170 x 700 x 215 mm (LxWxH)

100-240 VAC, 50/60 Hz or 12VDC (15 watts with heater inactive)

Comm ports include
- 4 analogue outputs (2 voltage & 2 current)
- RS232 multidrop
- RS232 serial port
Data storage up to 12 days of 1 minute data or 61 days of 5 minute data

Accessories - click on slide for more information

Accessories - Aurora 1000 integrating nephelometer

Accessories	Pt No.
Additional sample tube	Multiple
Roof flange kit	ECO-M9003004
Rain cap with insect screen	ECOM9003011
Gas calibration kit	H020331
Wall mount bracket	H020005
12V battery power cable	C020022

Spares/Consumables	Pt No.
Service kit	H020335
Zero/Span filter	FIL-1050
Zero pump filter	036-040180
Backup battery	BAT-AA

Case Studies

The Aurora Series of nephelometers are used around the world in a wide variety of applications ranging from monitoring aerosol properties important in radiative forcing models that measure climate change, to visibility applications in Australia and the USA, to dust storm warning systems in the Gobi desert of China and are even used in some regions as a surrogate measurement for PM2.5.

Below is an assortment of case studies that help outline the versatile nature of the Aurora nephelometers.

Dust Storm Monitoring in the Gobi Desert

Case Studies of China Meteorological Authority.

CMA Sand Storm Monitoring

Over the past 4 years the Chinese Meteorological Authority has deployed 22 Aurora Nephelometers to rural Chinese provinces to act as an early warning system for approaching dust storms. These instruments provide both details on ambient visibility along with aerosol scattering which is used for numerical forecasting of dust storms as well as fingerprinting particulate sources. These monitoring stations are connected via remote communication to CMA's office in Beijing.

china

CMA chose the Aurora Nephelometers for the following reasons

Lower cost of ownership

Lower power consumption (Low carbon footprint)
They didn't require air conditioned enclosures
ideal for remote locations
Low maintenance and easier to operate
Can measure high concentration (without clogging filter)

Vibration insensitive

Australian EPA National Ambient Monitoring Network

Australian EPA's Air Quality Monitoring Network

All of Australia's seven state EPAs have installed Aurora Nephelometers into their regional monitoring networks in accordance with Australian Standard AS/NZS 3580.12.1:2001 for the Determination of Light Scattering – Integrating Nephelometer Method. This network of nephelometer provides an excellent measure of ambient visibility. The nephelometers are calibrated on a regular basis automatically using a cylinder of CO2. Every quarter they are also checked against a cylinder of FM200.

The EPA's chose the Aurora Nephelometers for a variety of reasons which included:

Excellent accuracy and reliability when measurement the scattering coefficient
Easy to calibrate
Low maintenance - once per year cell cleaning
Easily integrated into their existing network

Link to Current Air Quality for New South Wales Australia

note: Visibility readings from Ecotech nephelometers

EPA Source Apportionment Study

Assigning a likely cause to Particle Events

Recently the Victorian EPA in collaboration with Latrobe University undertook a major study in order to compare Nephelometer data with Federal Equivalent Method data derived by Tapered Element Oscillating Microbalance PM10 monitors with the attempt to develop a low cost desktop method for assigning a likely cause to particle pollution events. The study looked at historical data from both instruments and produced a pollutant ratio.

What the study found was the following:

PM10/Scatt. Coff. - high values indicated a coarse mode event

PM10/scatt. coeff	Source of particulates
> 0.9	Sample is mostly coarse particles
<= 0.9	Sample is most likely fine particles
> 2.0	Likely to be windblown dust
< 0.38	Likely to be combustion smoke

This study demonstrated how using the Aurora Nephelometer , it possible to perform basic source apportionment when comparing Aurora Nephelometer data with data generated from a Federal Reference Method continuous PM monitor such as a TEOM or Beta Monitor. A comparison of the scattering coefficient to mass factor Coef_Scat/PMprovides useful information. For instance a shift in this factor indicates that the aerosols chemistry has changed and for instance smoke rich urban air is now being measured instead of desert dust. This information can be useful in estimating the degree of harm that PM concentrations may cause to human health as urban air may pose significantly higher risks than desert dust at the same concentration.

USEPA Regional Method Study

Equivalent Method Studies from North America

Washington State E.P.A. and the Mexican Federal EPA both commissioned studies to compare the Ecotech nephelometer against their reference PM2.5 methods. In both studies a high level of correlation between reference methods and the Ecotech nephelometer were observed with an R2 > 0.94 demonstrated. This served to illustrate how an integrating nephelometer could be used as a low maintenance, easily deployed replacement for the higher cost and maintenance heavy Federal Reference Methods which included the Tapered Element Oscillating Microbalance and the Beta Attenuation Method.

Comparison from Puget Sound - Washington State

Federal Reference Method vs Ecotech Nephelometer

puget sound