For the second consecutive day there were strong winds consistently from the west on Friday (24 km/hr – W and 20 km/h – W at 9 a.m. and 3 p.m. recorded at Archerfield). This again kept carbon dioxide concentrations unusually ‘low’ at all three sites, though the values were higher at the city centre site (Petrie Terrace) throughout the day, and remain higher on average for the last 21 days. (It should go without saying that the term ‘low’ is relative to the last three weeks – values some 100 ppm above pre-industrial levels are obviously anything but ‘low’ or ‘normal’ in a broader sense). How can Brisbane be experiencing carbon dioxide concentrations, temporarily, lower than those currently measured at Mauna Loa or Kennaook/Cape Grim (about 419 and 415 ppm respectively)? Such low ground-level values are possible when conditions move large volumes of air from outside the city, benefitting from photosynthesis effects, to predominate over urban anthropogenic sources. In the last couple of days Brisbane appears to have been experiencing just such conditions.
Daily Averages – Phase 2 (See explanation of differences between Phase 1 and Phase 2 data)
For reference, latest monthly average (May 2023) from CSIRO for Kennaook/Cape Grim in NW Tasmania was 415.7 ppm. (Note – these are provisional values, subject to revision folllowing sensor re-calibrations and other checks.)
| Date | Petrie Terrace | Chapel Hill | Bellbird Park |
| 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 | 4444 ppm |
| 9-Jun-2023 | 441 ppm | 428 ppm | 440ppm |