Introduction
Aeroqual monitors sold between May 2018 and November 2019 measure NO2 using a combined Ox/O3 module system.
Before then, NO2 was measured directly by its own large NO2 module. In November 2019, Aeroqual returned to a single (but smaller) module for measuring NO2 directly. These two NO2 modules are span calibrated like you would any other gas.
If your monitor contains the Ox/O3 system, span calibration involves some extra steps. It includes the calculation of an a value, and relies on the modules being calibrated in the following order:
- Ox gain (using NO2 calibration gas)
- O3 gain (using O3 calibration gas)
- NO2 a value (using O3 calibration gas)
- All other modules
When an Ox module is fitted, NO2 doesn’t have a zero or gain adjustment. The NO2 calibration (a adjustment) is performed during the ozone span gas delivery.
The a value should be checked and adjusted as part of your routine span calibration.
To understand how often you should perform this service activity, click here.
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Aeroqual monitors sold between May 2018 and November 2019 use the Ox and O3 modules to measure NO2.
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There are two ways to determine if you have an Ox module fitted:
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Open the Calibration and Service app. If Ox appears in the parameters and there’s data, it’s installed. If there’s no data, it may have been removed but not deleted from the sensor list.
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Look for the physical module in the monitor. You can identify the gas type by checking the barcode label of the module – the code includes the monitor type, the gas type and a unique number sequence, eg. AQM Ox 0-10ppm 0000000-000.
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This image shows the Ox and O3 modules side by side. Note: The power and communication cables have been removed for clarity.
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Record the initial NO2 a value in the Current a value column of your calibration form.
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This guide assumes the AirCal 1000 is already connected to the gas inlet via a 3-way tee that's open (uncapped) on one side.
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To calibrate the Ox module, start the NO2 calibration gas flowing at your chosen span point. Aeroqual recommends 0.1 ppm.
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Follow steps 3-11 in this guide to complete a span calibration for Ox.
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The NO2 module should read 0.1 ppm during the 0.1 ppm Ox span calibration. It might may read slightly less than 0.1. This is normal so don't adjust the NO2 gain.
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If the Ox module fails calibration, the NO2 measurement can’t be used but you can still calibrate the O3 module.
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To calibrate the O3 module, change the gas connection from the AirCal 1000 to the Ozone Calibration Source.
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Follow the steps in this guide to complete a span calibration for O3.
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If the O3 module fails calibration, the NO2 measurement can’t be used.
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During the O3 is calibration, the Ox module should show a response towards O3 calibration gas. Wait for the Ox values to stabilise towards O3.
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After the Ox values have stabilized, calculate the a value using the equation shown.
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The a value should be in the range 0.3 to 1.5.
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If your calculated a value falls outside this range, don’t change the a value. For support, contact Technical Support.
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Record the new a value in the New a value column.
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Upload the new a value for NO2 in the Manual Entry area of the Calibration and Service screen.
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Only the a value is set for NO2. The offset should be left at 0.000 and the gain should be left at 1.000.
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After you've uploaded the Ox gain, O3 gain and NO2 a value, record the current NO2 readings in the Reading after gain changed column.
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Don’t adjust any calibration settings for the NO2 channel.
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Disconnect the Ozone Calibration Source from your monitor and connect the AirCal 1000 calibrator.
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Remove the cap from the other side of the tee.
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Flow zero air for 10 minutes to purge (clean) the gas lines.
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For extra help, watch our video.
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For further support, contact Technical Support.
For further support, contact Technical Support.
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