Laboratory Evaluation
TSI AirAssure PM2.5 Sensor

Background
Three TSI AirAssure PM2.5 sensors (units IDs: 004, 005, and 010) were field-tested at theSouth Coast AQMD Rubidoux fixed ambient monitoring station (12/18/2015 to 02/15/2016)
under ambient environmental conditions. Now, three new AirAssure sensors (units IDs: 5036,7003, 7004) have been evaluated in the South Coast AQMD Chemistry Laboratory undercontrolled artificial aerosol concentration/size range, temperature, and relative humidity.
AirAssure Sensor (3 units tested): Particle sensors (optical; non-FEM)
 Each unit measures PM2.5 massconcentration (µg/m3)
 Unit cost: ~$1500
 Time resolution: 1-min
 Units IDs: 5036, 7003, 7004

GRIMM (reference method):Optical particle counterFEM PM2.5
Uses proprietary algorithms to calculate
total PM, PM2.5, and PM1 mass conc. fromparticle number measurements
Cost: ~$25,000
Time resolution: 1-min

TSI AirAssure
Model IPM2.5

FEM GRIMM
2

AirAssure vs FEM GRIMM (PM2.5 mass; 5-min mean)
Coefficient of Determination

TSI AirAssure vs GRIMM (PM2.5 mass conc. ramping, 20 °C, 40% RH)
GRIMM

Unit5036

Unit7003

Unit7004

GRIMM vs AirAssure
PM2.5 mass conc.
300

300

FEM GRIMM (µg/m3)

5-min Mean PM2.5 mass conc. (ug/m3)

350

250
200
150
100200(*GRIMM conc. higher than 150 µg/m3: not shown,b/c AirAssure plateaued at 300 µg/m3)

y = 0.50x - 5.37
R² > 0.99

10000100
200
300
Average of 3 AirAssure units (µg/m3)

5000150

300

450

600

750

Time (min)• The three AirAssure sensors tracked well with the concentration
variation recorded by FEM GRIMM in the concentration range of 0-150μg/m3.

• Three AirAssure sensors
showed very strong
correlations with GRIMM
PM2.5 mass conc. (R2 > 0.99)
between 0-150 μg/m3.

• AirAssure sensors overestimated the GRIMM PM2.5 mass conc, and stopped
to report values higher than 300 μg/m3 (when GRIMM measured above 150μg/m3). Sensor manufacturer claims a measurement range of 5-300 µg/m3.

3

PM2.5 Accuracy: AirAssure vs GRIMM• Accuracy (20 °C and 40% RH)

Steady State(#)

Sensor mean(µg/m3)

GRIMM(µg/m3)

Accuracy
(%)

1234

37.4
77.3
157.7
295.9

12.1
32.7
73.3
142.8

-108.1
-36.5
-15.2
-7.2

• AirAssure has low accuracy compared to FEM GRIMM. The three AirAssure sensors overestimatedFEM GRIMM PM2.5 measurements over the concentration range of 0-150 µg/m3.

AirAssure Data Recovery and Intra-model variability• Data recovery for PM2.5 mass concentration from 5036, 7003, and 7004 were 97.06%, 97.13%, and 97.13%.
• Moderate to high PM2.5 measurement variations were observed among the three AirAssure units.

4PM2.5 Precision: AirAssure• Precision (Effect of PM2.5 conc., Temperature and Relative Humidity)
Medium conc.

Low conc.
Relative Humidity 15%

40%

65%

Relative Humidity 15%

High conc.

40%

Relative Humidity 15%

65%

35 °C

35 °C

35 °C

20 °C

20 °C

20 °C

5 °C

5 °C

5 °C

9596

97
98
PRECISION (%)

99

100

95

96

97
98
PRECISION (%)

99

100

40%

65%

At high PM2.5 concentration(higher than 150 g/m3,
measured by GRIMM), AirAssure
plateaued at 300 g/m3.

9596

97
98
PRECISION (%)

99100• Overall, the three AirAssure sensors showed high precision for most of the combinations of low and medium
PM2.5 conc., T, and RH.
• At high PM2.5 concentration (higher than 150 µg/m3, measured by GRIMM), AirAssure plateaued at 300µg/m3.

5

AirAssure Climate Susceptibility
AirAssure vs GRIMM(5 C RH ramping, med PM2.5 mass conc.)
Unit5036

Unit7003

From 15% to 40% RH

Unit7004
To 65% RH

200150100

AirAssure vs GRIMM(35 C RH ramping, med PM2.5 mass conc.)
GRIMM

500050100150200

Time (min)Low Temp - RH ramping(medium conc.)

250

1-min mean PM2.5 mass conc. (ug/m3)

1-min mean PM2.5 mass conc. (ug/m3)

GRIMM

250

Unit5036

Unit7003

From 15% to 40% RH

Unit7004
To 65% RH

200150100500050100150200

250

Time (min)High Temp - RH ramping(medium conc.)
6Discussion
 Accuracy: Overall, the three AirAssure sensors have low accuracy, compared to GRIMM PM2.5 in therange of 0.0 to 150 µg/m3. AirAssure overestimated FEM GRIMM’s reading in the laboratory experiments.
 Precision: The AirAssure sensors have high precision for most of the test combinations (low, medium PM
concentrations, T and RH).
 Intra-model variability: Moderate to high intra-model variability was observed among the three AirAssuresensors.

 Data Recovery: Data recovery for PM2.5 mass concentration from 5036, 7003, 7004 was 97.06%,97.13%, and 97.13%.
 Coefficient of Determination: The three AirAssure sensors showed very strong correlation/linear
response with the corresponding GRIMM PM2.5 measurement data (R2 > 0.99) for mass concentration
range between 0 and 150 µg/m3.

 Climate susceptibility: For most of the temperature and relative humidity combination, the climate
condition had minimal effect on the AirAssure’s precision. At the set-points of RH changes at low PM
concentrations, AirAssure sensors had some small spikes.

7