Figure 1:
Figure 2:
Figure 3:
Figure 4:
Figure 5:
PurpleAir sensor data, Primary and Secondary data sets of Channels A and B, gray cells represent the selected parameters of the study (PurpleAir, 2022)
| PRIMARY | ||
|---|---|---|
| CHANNEL A | CHANNEL B | |
| Field 1 | PM1.0 (CF = 1) μg/m3 | PM1.0 (CF = 1) μg/m3 |
| Field 2 | PM2.5 (CF = 1) μg/m3 | PM2.5 (CF = 1) μg/m3 |
| Field 3 | PM10.0 (CF = 1) μg/m3 | PM10.0 (CF = 1) μg/m3 |
| Field 4 | Uptime (min) | Free HEAP memory |
| Field 5 | RSSI (WiFi signal strength) | ADC0 (analog input) voltage |
| Field 6 | Temperature (F) | FIRMWARE 2.5 and up: atmospheric pressure |
| Field 7 | Humidity (%) | FIRMWARE 4.10 and up: Bosch BSEC IAQ when BME680 gas sensor is present |
| Field 8 | PM2.5 (CF = ATM) μg/m3 | PM2.5 (CF = ATM) μg/m3 |
| SECONDARY | ||
| Field 1 | 0.3 μm particles/dL | 0.3 μm particles/dL |
| Field 2 | 0.5 μm particles/dL | 0.5 μm particles/dL |
| Field 3 | 1.0 μm particles/dL | 1.0 μm particles/dL |
| Field 4 | 2.5 μm particles/dL | 2.5 μm particles/dL |
| Field 5 | 5.0 μm particles/dL | 5.0 μm particles/dL |
| Field 6 | 10.0 μm particles/dL | 10.0 μm particles/dL |
| Field 7 | PM1.0 (CF = ATM) μg/m3 | PM1.0 (CF = ATM) μg/m3 |
| Field 8 | PM10 (CF = ATM) μg/m3 | PM10 (CF = ATM) μg/m3 |
OK RMSE of hourly temperature data on 2019-05-24 00:00:00 UTC, before and after outlier filter for 10 repetitions
| Before filter | 4,083.351 | 8,997.641 | 4,102.043 | 4,080.238 | 544.752 | 4,141.303 | 426.213 | 4,087.449 | 8,030.859 | 3,272.878 |
| After filter | 0.209 | 0.540 | 0.501 | 0.204 | 0.155 | 0.507 | 0.285 | 0.312 | 0.503 | 0.245 |
IQR and GESD outliers on daily data without duplicates, for Temperature (°C), Humidity (%), and PM (1_0 μm/m3, 2_5 μm/m3, 10_0 μm/m3) before and after filter application
| BEFORE FILTER | |||||||
|---|---|---|---|---|---|---|---|
| Observations (n) | IQR outliers (n) | GESD outliers (n) | Outlier observations in both methods (n) | IQR outliers/observations (%) | GESD outliers/observations (%) | Both methods/observations (%) | |
| Temperature (°C) | 29,040 | 380 | 735 | 380 | 1.3 | 2.5 | 1.3 |
| Humidity (%) | 29,040 | 94 | 234 | 94 | 0.3 | 0.8 | 0.3 |
| PM1.0 μm/m3 cf_1 | 29,437 | 665 | 1,302 | 665 | 2.3 | 4.4 | 2.3 |
| PM2.5 μm/m3 cf_1 | 29,437 | 716 | 1,494 | 708 | 2.4 | 5.1 | 2.4 |
| PM10.0 μm/m3 cf_1 | 29,437 | 751 | 1,552 | 751 | 2.6 | 5.3 | 2.6 |
| PM1.0 μm/m3 cf_atm | 29,435 | 560 | 835 | 553 | 1.9 | 2.8 | 1.9 |
| PM2.5 μm/m3 cf_atm | 29,437 | 596 | 926 | 596 | 2.0 | 3.1 | 2.0 |
| PM10.0 μm/m3 cf_atm | 29,435 | 608 | 1,051 | 606 | 2.1 | 3.6 | 2.1 |
| AFTER FILTER | |||||||
| Temperature (°C) | 28,552 | 221 | 579 | 221 | 0.8 | 2.0 | 0.8 |
| Humidity (%) | 29,040 | 94 | 234 | 94 | 0.3 | 0.8 | 0.3 |
| PM1.0 μm/m3 cf_1 | 29,316 | 554 | 1,188 | 554 | 1.9 | 4.1 | 1.9 |
| PM2.5 μm/m3 cf_1 | 29,316 | 592 | 1,360 | 584 | 2.0 | 4.6 | 2.0 |
| PM10.0 μm/m3 cf_1 | 29,316 | 624 | 1,417 | 624 | 2.1 | 4.8 | 2.1 |
| PM1.0 μm/m3 cf_atm | 29,316 | 443 | 713 | 436 | 1.5 | 2.4 | 1.5 |
| PM2.5 μm/m3 cf_atm | 29,318 | 485 | 807 | 485 | 1.7 | 2.8 | 1.7 |
| PM10.0 μm/m3 cf_atm | 29,316 | 495 | 930 | 493 | 1.7 | 3.2 | 1.7 |
Outliers of IQR and GESD methods on daily data for temperature (°C), humidity (%), and PM (1_0 μm/m3, 2_5 μm/m3, 10_0 μm/m3) before and after filter application
| BEFORE FILTER | |||||||
|---|---|---|---|---|---|---|---|
| Observations (n) | IQR outliers (n) | GESD outliers (n) | Outlier observations in both methods (n) | IQR outliers/observations (%) | GESD outliers/observations (%) | Both methods/observations (%) | |
| Temperature (°C) | 45,740 | 1,094 | 1,932 | 1,034 | 2.4 | 4.2 | 2.3 |
| Humidity (%) | 45,740 | 260 | 556 | 260 | 0.6 | 1.2 | 0.6 |
| PM1.0 μm/m3 cf_1 | 46,305 | 1,655 | 2,745 | 1,655 | 3.6 | 5.9 | 3.6 |
| PM2.5 μm/m3 cf_1 | 46,305 | 1,822 | 3,042 | 1,815 | 3.9 | 6.6 | 3.9 |
| PM10.0 μm/m3 cf_1 | 46,305 | 1,869 | 3,146 | 1,862 | 4.0 | 6.8 | 4.0 |
| PM1.0 μm/m3 cf_atm | 46,299 | 1,498 | 2,019 | 1,488 | 3.2 | 4.4 | 3.2 |
| PM2.5 μm/m3 cf_atm | 46,305 | 1,632 | 2,193 | 1,537 | 3.5 | 4.7 | 3.3 |
| PM10.0 μm/m3 cf_atm | 46,299 | 1,762 | 2,558 | 1,626 | 3.8 | 5.5 | 3.5 |
| AFTER FILTER | |||||||
| Temperature (°C) | 44,928 | 624 | 1,470 | 624 | 1.4 | 3.3 | 1.4 |
| Humidity (%) | 45,740 | 260 | 556 | 260 | 0.6 | 1.2 | 0.6 |
| PM1.0 μm/m3 cf_1 | 46,091 | 1,386 | 2,449 | 1,378 | 3.0 | 5.3 | 3.0 |
| PM2.5 μm/m3 cf_1 | 46,091 | 1,549 | 2,738 | 1,545 | 3.4 | 5.9 | 3.4 |
| PM10.0 μm/m3 cf_1 | 46,091 | 1,598 | 2,854 | 1,593 | 3.5 | 6.2 | 3.5 |
| PM1.0 μm/m3 cf_atm | 46,089 | 1,232 | 1,741 | 1,225 | 2.7 | 3.8 | 2.7 |
| PM2.5 μm/m3 cf_atm | 46,095 | 1,376 | 1,897 | 1,282 | 3.0 | 4.1 | 2.8 |
| PM10.0 μm/m3 cf_atm | 46,089 | 1,475 | 2,231 | 1,340 | 3.2 | 4.8 | 2.9 |
Outliers of IQR and GESD methods on hourly data for temperature (°C), humidity (%), and PM (1_0 μm/m3, 2_5 μm/m3, 10_0 μm/m3) before and after filter application
| BEFORE FILTER | |||||||
|---|---|---|---|---|---|---|---|
| Observations (n) | IQR outliers (n) | GESD outliers (n) | Outlier observations in both methods (n) | IQR outliers/observations (%) | GESD outliers/observations (%) | Both methods/observations (%) | |
| Temperature (°C) | 1,074,342 | 5,643 | 7,471 | 4,272 | 0.4 | 0.7 | 0.4 |
| Humidity (%) | 1,074,342 | 6,373 | 7,196 | 6,026 | 0.6 | 0.7 | 0.6 |
| PM1.0 μm/m3 cf_1 | 1,087,434 | 49,742 | 70,944 | 48,046 | 4.4 | 6.5 | 4.4 |
| PM2.5 μm/m3 cf_1 | 1,087,434 | 52,848 | 73,647 | 51,091 | 4.7 | 6.8 | 4.7 |
| PM10.0 μm/m3 cf_1 | 1,087,434 | 54,936 | 75,768 | 53,141 | 4.9 | 7.0 | 4.9 |
| PM1.0 μm/m3 cf_atm | 1,087,362 | 37,216 | 46,946 | 34,170 | 3.4 | 4.3 | 3.1 |
| PM2.5 μm/m3 cf_atm | 1,087,434 | 38,954 | 46,011 | 34,936 | 3.6 | 4.2 | 3.2 |
| PM10.0 μm/m3 cf_atm | 1,087,362 | 49,344 | 67,686 | 45,595 | 4.5 | 6.2 | 4.2 |
| AFTER FILTER | |||||||
| Temperature (°C) | 1,056,463 | 2,984 | 4,682 | 2,812 | 0.3 | 0.4 | 0.3 |
| Humidity (%) | 1,074,342 | 6,373 | 7,196 | 6,026 | 0.6 | 0.7 | 0.6 |
| PM1.0 μm/m3 cf_1 | 1,082,638 | 46,121 | 67,057 | 44,444 | 4.3 | 6.2 | 4.1 |
| PM2.5 μm/m3 cf_1 | 1,082,631 | 49,387 | 69,968 | 47,650 | 4.6 | 6.5 | 4.4 |
| PM10.0 μm/m3 cf_1 | 1,082,619 | 50,824 | 71,449 | 49,052 | 4.7 | 6.6 | 4.5 |
| PM1.0 μm/m3 cf_atm | 1,082,576 | 33,896 | 43,637 | 30,887 | 3.1 | 4.0 | 2.9 |
| PM2.5 μm/m3 cf_atm | 1,082,646 | 35,257 | 42,116 | 31,249 | 3.3 | 3.9 | 2.9 |
| PM10.0 μm/m3 cf_atm | 1,082,573 | 45,929 | 63,842 | 42,188 | 4.2 | 5.9 | 3.9 |
IQR and GESD outliers on hourly data without duplicates, for Temperature (°C), Humidity (%), and PM (1_0 μm/m3, 2_5 μm/m3, 10_0 μm/m3) before and after filter application
| BEFORE FILTER | |||||||
|---|---|---|---|---|---|---|---|
| Observations (n) | IQR outliers (n) | GESD outliers (n) | Outlier observations in both methods (n) | IQR outliers/observations (%) | GESD outliers/observations (%) | Both methods/observations (%) | |
| Temperature (°C) | 682,028 | 3,533 | 4,763 | 3,531 | 0.5 | 0.7 | 0.5 |
| Humidity (%) | 682,028 | 2,685 | 3,817 | 2,685 | 0.4 | 0.6 | 0.4 |
| PM1.0 μm/m3 cf_1 | 691,210 | 28,161 | 40,473 | 28,161 | 4.1 | 5.9 | 4.1 |
| PM2.5 μm/m3 cf_1 | 691,210 | 29,515 | 42,624 | 29,515 | 4.3 | 6.2 | 4.3 |
| PM10.0 μm/m3 cf_1 | 691,210 | 30,364 | 43,831 | 30,364 | 4.4 | 6.3 | 4.4 |
| PM1.0 μm/m3 cf_atm | 691,159 | 18,076 | 22,099 | 18,074 | 2.6 | 3.2 | 2.6 |
| PM2.5 μm/m3 cf_atm | 691,210 | 18,874 | 23,095 | 18,866 | 2.7 | 3.3 | 2.7 |
| PM10.0 μm/m3 cf_atm | 691,159 | 22,396 | 33,156 | 22,020 | 3.2 | 4.8 | 3.2 |
| AFTER FILTER | |||||||
| Temperature (°C) | 671,277 | 2,068 | 3,486 | 2,066 | 0.3 | 0.5 | 0.3 |
| Humidity (%) | 682,028 | 2,685 | 3,817 | 2,685 | 0.4 | 0.6 | 0.4 |
| PM1.0 μm/m3 cf_1 | 688,544 | 26,450 | 38,706 | 26,450 | 3.8 | 5.6 | 3.8 |
| PM2.5 μm/m3 cf_1 | 688,537 | 27,692 | 40,662 | 27,692 | 4.0 | 5.9 | 4.0 |
| PM10.0 μm/m3 cf_1 | 688,527 | 28,398 | 41,690 | 28,398 | 4.1 | 6.1 | 4.1 |
| PM1.0 μm/m3 cf_atm | 688,500 | 16,234 | 20,235 | 16,232 | 2.4 | 2.9 | 2.4 |
| PM2.5 μm/m3 cf_atm | 688,549 | 17,050 | 21,219 | 17,042 | 2.5 | 3.1 | 2.5 |
| PM10.0 μm/m3 cf_atm | 688,497 | 20,508 | 31,115 | 20,132 | 3.0 | 4.5 | 2.9 |