Near Reference refers to a combination of technologies – underpinned by Aeroqual’s unique intellectual property – that allow the AQS-1 product to take ambient air quality measurements very close to those of traditional ‘reference’ analyzers.
Aeroqual selects the very best sensor for the target gas and application. Because the company manufactures sensors, it has the expertise to know how to assess sensors from other manufacturers. Over the last decade, Aeroqual has tested hundreds of sensors against strict criteria – for selectivity, sensitivity and stability. Lab testing is followed by testing in real field conditions, in hot dry conditions, cold and wet and everything in between.
Sensor Module Design
Each sensor module includes components that compensate for any weaknesses of a sensor and to extend its operating life. For example, the SO2 module includes the sensor plus a flow control orifice, solenoid, scrubbers, humidity equalizer, and electronics. These additional components compensate for sensor drift, noise, humidity and cross interference, and improve the minimum detection limit in real world conditions.
High measurement accuracy starts with a high quality calibration. The sensor modules are calibrated against gas standards prepared under ISO 6143 to ensure traceability to reference materials from National Metrology Institutes. Gas mixtures are prepared by dilution using calibrated mass flow controllers and zero grade air and delivered to the sensors via inert PTFE tubing. The calibration procedures are regularly checked by ISO9001 and MCERTS auditors.
Many (but not all) air quality sensors are sensitive to changes in temperature. Small changes in ambient temperature may not affect ppm level measurements but can seriously affect measurements at the ppb level. In the AQS 1, Aeroqual uses only sensor modules that do not exhibit temperature interference. Other Aeroqual
Active Sampling System
The stainless steel sampling inlet is lined with an inert material that ensures no target pollutant is lost. The sampled air passes through a PTFE filter that removes particulate, protecting the sensors and extending their life. Air is drawn continuously by a brushless DC pump that works with the flow control orifice in each module to deliver a precise flow of air to the sensor. This allows a higher degree of confidence in the measurement. Finally, exhaust gas is released well away from the inlet.
Unlike all other sensor-based air quality monitors, the AQS products are designed to be calibrated in the field, using the same standard reference materials as a US EPA / EU certified analyser (i.e. calibration gas and dilution calibrators). Field calibration at the sampling location ensures that the measurements are traceable and the air quality data is robust and defensible. A calibration record is automatically captured in the AQS digital journal (accessible online in real- time).