• Chamber System Schematic
  • IMG_2237
  • Laboratory Chamber System

Laboratory Evaluations

Sensors that demonstrated a nominal level of performance in the field are brought back to the AQ-SPEC laboratory, where a “characterization chamber” is used to challenge the sensors with known concentrations of gases and particles under controlled temperature (T) and relative humidity (RH) levels. Sensors are evaluated in a group of triplicate to provide better statistical information about the comparability with FRM/FEM instruments or, widely accepted Best Available Technology instruments measuring the same pollutant(s). A Laboratory Testing Protocol has been developed to properly characterize sensor performance.

Several parameters are measured for evaluating the performance of a sensor technology under AQ-SPEC including:

  • Detection range: nominal minimum and maximum concentrations that a method is capable of measuring
  • Linearity: correlation (R2) between co-located sensor and FRM/FEM/BAT concentration measurements
  • Detection limit: lowest pollutant concentration that a sensor can reliably detect
  • Accuracy: degree of closeness of sensor concentration measurements to the actual (true) concentration value measured using FRM/FEM/BAT instruments
  • Precision: variation around the mean of repeated measurements of the same pollutant concentration
  • Response time: how quickly does the sensor respond to changing conditions
  • Co-pollutant interference: positive or negative measurement response caused by a pollutant other than the one being measured
  • Temperature (T) and Relative Humidity (RH) influences: positive or negative measurement response caused by variations in T and RH

Laboratory Evaluation Reports

The correlation coefficient (R2) is a statistical parameter indicating how well the performance of each sensor compares to that of a Federal Reference Method (FRM), Federal Equivalent Method (FEM) or Best Available Technology (BAT) instrument. An R2 approaching the value of 1 reflects a near perfect agreement, whereas a value of 0 indicates a complete lack of correlation. All R2 values reported in these reports are based either on a 5-min or 1-hr average data. The Lab R2 values are also based on the average ambient conditions (20 degrees C and 40% RH) experiment in the chamber. An ad-hoc rating system will be developed to summarize the overall performance of these sensors.

Disclaimer

All documents, reports, data, and other information provided on this website are for informational use only. The majority of sensors evaluated as part of the Air Quality-Sensor Performance Evaluation Center (AQ-SPEC) program were field-tested inside a custom-made aluminum enclosure to protect the sensors from windblown rain, harsh sunlight, and animals. The field evaluations reports included on this website contain data collected at our monitoring station during a specific 30- to 60-day period and may not be duplicated at the same or different location, season, time period, or weather conditions (e.g. temperature, relative humidity, pressure, wind speed/direction). As the overall sensor performance may be affected by the specific environmental conditions experienced at our location during the time of testing, replication and/or duplication may not possible to achieve. The laboratory evaluation was conducted in the AQ-SPEC’s environmental chamber with simulated pollutant and interferent concentrations that were generated from nebulizer solutions, dust dispensers, and gas dilution calibrators. Generated environments may not be able to fully replicate the conditions that may be experienced under ambient settings. The sensor assembly, installation, and use can also impact the reliability of the products evaluated by the AQ-SPEC program. South Coast Air Quality Management District (SCAQMD) makes no claim, warranty, or guarantee that these devices will or will not work when operated by other users for their specific applications.

The South Coast AQMD AQ-SPEC program in the Quality Assurance division of the Science and Technology Advancement office aims at providing information to and for the benefit of the public to make informed purchasing decisions on commercially available “low cost” air quality sensor devices. In accordance with this mission, the general policy of the Board of the Agency is to exclude from the AQ-SPEC website all commercial advertising and promotional material, including links which provide exclusive private or financial benefit to commercial, non-public enterprises and which do not promote or enhance a public benefit to the general public. As a government agency, the SCAQMD neither endorses nor supports individual private commercial enterprises through display of their products on the AQ-SPEC website or through providing links to the sites of such commercial enterprises.