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NOW AVAILABLE: South Coast AQMD Evaluates the ES-405 for their Air Quality Sensor Performance Evaluation Center (AQ-SPEC) Program

South Coast AQMD has established the Air Quality Sensor Performance Evaluation Center (AQ-SPEC) program to evaluate the performance of “low-cost” air quality sensors.

The ES-405 is a new near-reference air quality sensor designed to provide accurate real-time measurements of PM10, PM4, PM2.5, and PM1 particulate concentrations simultaneously.

From December 24, 2020, to February 24, 2021, three Met One Instruments, Inc. ES-405 Particulate Profilers were deployed at the South Coast AQMD stationary ambient monitoring site in Rubidoux, California. The ES-405’s were run side-by-side with Federal Equivalent Method (FEM) instruments measuring PM1.0, PM2.5, and PM10. Five-minute, one-hour, and 24-hour data averages were compared to evaluate performance.

What are the Preliminary Findings of the ES-405 Measurement Accuracy?

PM2.5 1-hour Mean, ES-405 vs. FEM T640

PM1.0 and PM10 mass concentrations measured by the ES-405 sensors showed strong to very strong correlations with the corresponding FEM units.  PM2.5 mass concentrations measured by the ES-405 sensors showed moderate to very strong correlations with the corresponding FEM units.

Test results show very low Mean Absolute Error (MAE) as compared to FEM equipment.  MAE is the absolute difference between the sensors and the reference instruments.  Larger MAE values coincide with higher measurement errors.

5-min2.8 to 3.63.5 to 4.04.5 to 8.9
1-hr2.8 to 3.53.4 to 5.13.8 to 8.6
24-hr2.5 to 3.22.6 to 3.72.9 to 7.3
Mean Absolute Error of ES-405 Compared to FEM Equipment
PM1 5-minute Mean, ES-405 vs. FEM T640

Although the field tests reflect the most realistic in-situ results, these results are still preliminary as the South Coast AQMD goes on to conduct laboratory tests on the units. The laboratory tests will show how results change with varying environmental factors, such as temperature and humidity.

2023 UPDATE: Although the mass concentrations recorded by the ES-405 units were low when compared with the T640 reference, this variance has been remedied by an update to the T640 software, which now adjusts the T640 readings *down*. With the new T640 software in place, we can infer that the ES-405 readings would more closely match the T640 if this test were replicated today.

These exciting preliminary results show that the ES-405, a Non-Regulatory Supplemental & Informational Monitor (NSIM), is an excellent choice for low-cost sensor technology, with data tracking very closely to Federal Equivalent Method instrumentation. Among all low-cost sensors tested by South Coast AQMD for the AQ-SPEC program, the ES-405 Particulate Profiler showed the lowest Mean Absolute Error for PM10.

PM10 24-hour mean, ES-405 vs. FEM BAM

Want to Dig Deeper?

➡️ Read the full South Coast AQMD Field Evaluation of the ES-405 here!

➡️ Learn about Met One’s new standout particle monitor, the ES-405, which offers the capability of monitoring four PM sizes simultaneously in one instrument with exceptional accuracy at an affordable price.

➡️ Need more information on Met One Instruments, Inc. NSIM Devices? Check out Non-Regulatory Supplemental & Informational Monitors

➡️ Why should you choose MOI Low-Cost sensors? Learn more about the EPA’s report here.

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