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VOC Sensor Evaluations

South Coast AQMD’s AQ-SPEC program aims at being the testing center for low cost air monitoring sensors to establish performance standards by which sensors are evaluated. The program evaluates sensors in both controlled laboratory conditions and in the field. Ideally two triplicate sets of VOC sensors from the same production and quality control (QC) batch will be tested simultaneously in the field and laboratory. If only one triplicate can be obtained, the sensors will first be evaluated in the laboratory under known controlled conditions and concentrations of VOC concentrations, and then proceed to field evaluation if they demonstrate acceptable performance to warrant further evaluation efforts.

VOC Sensors
Sensor Image	Make (Model)	Est. Cost(USD)	Type	Meas.	*^Field R²**	*^Lab** R²	*^Field MAE (ppm)**	*^Lab MAE (ppm)**	Summary Report
	Aeroqual (S500-GSS)	$1650	Metal Oxide	tVOC		-		-
	Aeroqual (S500-PID)	$3120	Photoionization Detection	tVOC		Low ramp: 0.98		Low ramp: 0.22-0.48
						High ramp: 0.99		High ramp: 0.05-1.17
	Fablab (Smart Citizen Kit v2.1)	$119	Metal Oxide	tVOC		Low ramp: 0.69-0.73		Low ramp: 0.41-0.43
						High ramp: N/A		High ramp: N/A
	PurpleAir (PA-II-FLEX VOC)	$289	Metal Oxide	tVOC		Low ramp: Negative Correlation		Low ramp: N/A
						High ramp: 0.40-0.60		High ramp: N/A
	Sensirion (SGP40)	$80	Metal Oxide	tVOC		Low ramp: 0.91		Low ramp: 0.03-0.34
						High ramp: 0.01		High ramp: ~5.00

*The coefficient of determination (R²) is a statistical parameter measuring the degree of relation between two variables. Here, it measures the linear relationship between the sensor and the Best Available Technology (BAT) reference instrument. An R² approaching the value of 1 reflects a near perfect correlation, whereas a value of 0 indicates a complete lack of correlation. The mean absolute error (MAE) is a statistical parameter measuring the average of the absolute difference between the sensor and BAT reference instrument, without considering the direction of errors. Higher MAE values indicate higher sensor measurement error when compared to the BAT reference instrument. Field R² and MAE values are reported as a range based on the data for all sensor units evaluated, with sensor and BAT reference instrument data aggregated into 5-minute averages. Lab R² and MAE values are reported as two ranges (one for the low initial concentration ramping experiment and another for the high initial concentration ramping experiment) based on the data for all sensor units evaluated in the chamber under ambient conditions (20 degrees C and 40% RH) using the VOC blend, and based either on 5-minute averaged sensor and BAT data for real or near-real time BAT instruments, or the most recent sensor measurement for each BAT data point for non-real time BAT instruments. Lab MAE values consider data only during the Medium VOC blend concentration step (see testing protocol) for the respective concentration ramping experiment.

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) 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 AQ-SPEC. South Coast Air Quality Management District (South Coast AQMD) makes no claim, warranty, or guarantee that these devices will or will not work when operated by other users for their specific applications.

South Coast AQMD's AQ-SPEC 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 Governing 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 South Coast AQMD 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.

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VOC Sensor Evaluations

VOC Sensors

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