We have taken the last few weeks to make additional improvements to the calibration and analysis of our sensor data. This includes a more highly controlled process for a span calibration using an acccurate reference gas at 400 ppm, re-setting each sensor to that level, and then taking measurements of CO2 at incremental concentrations up to 520 ppm. Separately, we assess the response of each sensor to changes in relative humidity, temperature and air pressure with a constant CO2 concentration so these can be accurately compensated for. Finally, data are now normalised to 20 degrees C and 101.325 hPa (Normal Temperature and Pressure – NTP), and 50% RH (close to Brisbane’s annual average). This step improves the comparability of data from sensors in different locations. Calibration coefficients have been obtained for each individual sensor as they all have slightly different characteristics.
The data-graphing uses updated analysis code which applies the various coefficients and uses a low pass Butterworth filter to remove the occasional spike artifact. We’re no longer using the 30 minute averaging which tended to smooth data (but also remove detail) previously. To distinguish from previously reported data we are labelling this “Phase 3”. Despite these changes, the overall levels appear to be quite similar to those using the earlier calibrations in previous phases..
Daily Averages – Phase 3
| Date | Petrie Terrace | Chapel Hill | Bellbird Park |
| 21-Nov-2023 | 440 ppm | 436 ppm | 432 ppm |
Daily Averages – Phase 2 (See explanation of differences between Phase 1 and Phase 2 data)
For reference, latest monthly average (July 2023) from CSIRO for Kennaook/Cape Grim in NW Tasmania was 416.6 ppm. (Note – these are provisional values, subject to revision folllowing sensor re-calibrations and other checks.)
| Date | Petrie Terrace | Chapel Hill | Bellbird Park |
| 19-Aug-2023 | — | 396 ppm | 398 ppm |
| 18-Aug-2023 | 421 ppm | 417 ppm | 418 ppm |
| 17-Aug-2023 | 436 ppm | 425 ppm | 426 ppm |
| 16-Aug-2023 | — | 421 ppm | 420 ppm |
| 15-Aug-2023 | — | 426 ppm | 419 ppm |
| 14-Aug-2023 | 436 ppm | 430 ppm | 430 ppm |
| 13-Aug-2023 | 438 ppm | 428 ppm | 423 ppm |
| 12-Aug-2023 | 436 ppm | 426 ppm | 433 ppm |
| 11-Aug-2023 | 438 ppm | 427 ppm | 430 ppm |
| 10-Aug-2023 | 437 ppm | 427 ppm | 430 ppm |
| 09-Aug-2023 | 431 ppm | 427 ppm | 433 ppm |
| 08-Aug-2023 | 427 ppm | 428 ppm | 436 ppm |
| 07-Aug-2023 | 431 ppm | 427 ppm | 432 ppm |
| 06-Aug-2023 | 431 ppm | 431 ppm | 433 ppm |
| 05-Aug-2023 | 432ppm | 431 ppm | 434 ppm |
| 04-Aug-2023 | 436 ppm | 433 ppm | 435 ppm |
| 03-Aug-2023 | 434 ppm | 432 ppm | 423 ppm |
| 02-Aug-2023 | 432 ppm | 433 ppm | 415 ppm |
| 01-Aug-2023 | 440 ppm | 436 ppm | 431 ppm |
| 31-Jul-2023 | 443 ppm | 431 ppm | 430ppm |
| 30-Jul-2023 | 433 ppm | 424 ppm | 430 ppm |
| 29-Jul-2023 | 434 ppm | 424 ppm | 431 ppm |
| 28-Jul-2023 | 431 ppm | 424 ppm | 426 ppm |
| 27-Jul-2023 | 429 ppm | 430 ppm | 433 ppm |
| 26-Jul-2023 | 432 ppm | 431 ppm | 430 ppm |
| 25-Jul-2023 | 427 ppm | 425 ppm | 424 ppm |
| 24-Jul-2023 | 420 ppm | 418 ppm | 418 ppm |
| 23-Jul-2023 | 424 ppm | 421 ppm | 420 ppm |
| 22-Jul-2023 | 434 ppm | 429 ppm | 428 ppm |
| 21-Jul-2023 | 446 ppm | 430 ppm | — |
| 20-Jul-2023 | 433 ppm | 430 ppm | — |
| 19-Jul-2023 | 437 ppm | 436 ppm | 439 ppm |
| 18-Jul-2023 | 443 ppm | 432ppm | 433 ppm |
| 17-Jul-2023 | 435 ppm | 432 ppm | 436 ppm |
| 16-Jul-2023 | 436 ppm | 432 ppm | 441 ppm |
| 15-Jul-2023 | 449 ppm | 434 ppm | 452 ppm |
| 14-Jul-2023 | 452 ppm | 435 ppm | 448 ppm |
| 13-Jul-2023 | 433 ppm | 431 ppm | 429 ppm |
| 12-Jul-2023 | 437 ppm | 437 ppm | 438 ppm |
| 11-Jul-2023 | 448 ppm | 434 ppm | 438 ppm |
| 10-Jul-2023 | 439 ppm | 424 ppm | 432 ppm |
| 9-Jul-2023 | 423 ppm | 411 ppm | 417 ppm |
| 8-Jul-2023 | 418 ppm | 411 ppm | 414 ppm |
| 7-Jul-2023 | 413 ppm | 407 ppm | 408 ppm |
| 6-Jul-2023 | 434 ppm | 427 ppm | 428 ppm |
| 5-Jul-2023 | 442 ppm | 441 ppm | 429 ppm |
| 4-Jul-2023 | 449 ppm | 443 ppm | 429 ppm |
| 3-Jul-2023 | 428 ppm | 429 ppm | 412 ppm |
| 2-Jul-2023 | 424 ppm | 425 ppm | 414 ppm |
| 1-Jul-2023 | 419 ppm | 407 ppm | 405 ppm |
| 30-Jun-2023 | 414 ppm | 405 ppm | 402 ppm |
| 29-Jun-2023 | 415 ppm | 409 ppm | 405 ppm |
| 28-Jun-2023 | 435 ppm | 427 ppm | 428 ppm |
| 27-Jun-2023 | 426 ppm | 409 ppm | 415 ppm |
| 26-Jun-2023 | 412 ppm | 402 ppm | 412 ppm |
| 25-Jun-2023 | 447 ppm | 426 ppm | 429 ppm |
| 24-Jun-2023 | 427 ppm | 417 ppm | 423 ppm |
| 23-Jun-2023 | 434 ppm | 427 ppm | 435 ppm |
| 22-Jun-2023 | 442 ppm | 425 ppm | 436 ppm |
| 21-Jun-2023 | 443 ppm | 421 ppm | 437 ppm |
| 20-Jun-2023 | 421 ppm | 414 ppm | 417 ppm |
| 19-Jun-2023 | 430 ppm | 418 ppm | 419 ppm |
| 18-Jun-2023 | 436 ppm | 426 ppm | 434 ppm |
| 17-Jun-2023 | 440 ppm | 429 ppm | 437 ppm |
| 16-Jun-2023 | 438 ppm | 421 ppm | 433 ppm |
| 15-Jun-2023 | 433 ppm | 412 ppm | 428 ppm |
| 14-Jun-2023 | 435 ppm | 425 ppm | 438 ppm |
| 13-Jun-2023 | 441 ppm | 436 ppm | 442 ppm |
| 12-Jun-2023 | 442 ppm | 439 ppm | 448ppm |
| 11-Jun-2023 | 443 ppm | 441 ppm | 451 ppm |
| 10-Jun-2023 | 446 ppm | 432 ppm | 444 ppm |
| 9-Jun-2023 | 441 ppm | 428 ppm | 440ppm |