Brisbane's average carbon dioxide concentration for 13 October 2024: 440 ppm.
Average for 2023*: 427 ppm.
*Average of calendar year’s observations – based on three phases of data collection with different calibrations and incomplete data (64% complete).
With additional sites, we can learn more about Brisbane’s CO2 levels and their associations with weather, traffic etc. If you are interested in hosting a sensor, please contact us here.
Last year we visited Naomi Asimow at UC Berkeley, a Ph.D. student with the team who have been running the most comprehensive project of this type – in the San Francisco Bay Area.
She is the lead author of a recent paper reporting a 5-year analysis that shows an annual decline in CO2 concentrations of 1.8% per year – attributed largely to a 2.6% annual improvement rate in the efficiency of the vehicle fleet, with EVs and hybrids comprising a growing proportion of vehicles, and the gradual retirement of older, less efficient vehicles.
While more extensive and sophisticated than our network, this report illustrates the value of “ground-truthing” greenhouse gas levels in cities, given that bottom-up inventories can be quite inaccurate. Read the paper here.
Unfortunately, the rate of CO2 reduction the team reports is far slower than the trajectory required to meet San Francisco’s 2040 net zero target. And as for Brisbane, continued population growth, an anaemic rate of EV adoption, poor fuel standards and the popularity of ever larger utes and SUVs, does not bode especially well for our own outlook.
Daily profiles
We have been updating software and undertaking sensor recalibrations in the last week, so apologies for a few days without data. We are in the process of upating our data table to take better account of sensor drift in between calibrations, as well as correcting for some faulty humidity records from one of the BME280 sensors. The table is therefore unavailable until these corrections have been completed.
Why the high overnight values at Bellbird Park? Contrary to most reports (outer urban areas having lower carbon dioxide concentrations than city centres), we quite frequently observe high values at Bellbird Park. We cannot definitively attribute this to any specific source, but note that it is confined to night-time build-ups. One hypothesis is that there are several potential emissions sources in the area – including a slaughter-house, two refuse stations, and at least three large-scale composting operations. This article summarises some of what is known about emissions from composting: Nordahl, S.L. et al. (2023) ‘Greenhouse Gas and Air Pollutant Emissions from Composting’, Environmental Science & Technology, 57(6), pp. 2235–2247. Available at: https://doi.org/10.1021/acs.est.2c05846.
Please see below for a very interesting recent report from San Francisco’s BEACO2N network – which inspired our own project. The report this last week has had significant media coverage including the Los Angeles Times, pointing out the value of such networks:
“I think the best contribution this makes is showing how we can check what’s going on,” said Danny Cullenward, a climate economist and senior fellow at the Kleinman Center for Energy Policy at the University of Pennsylvania. “It’s probably not the last word. But it’s an elegant way to ground-truth some of these things. We need more of these approaches, not fewer.”
A network of sensors that includes carbon dioxide measurement is being installed in Providence, Rhode Island, adding to the handful of cities with continuous monitoring: https://www.breatheprovidence.com/.
Globally, 2024 continues to show some exceptional temperatures. Global sea surface temperature, for example, (dark line), has only recently fallen below levels for 2023, while remaining much higher than earlier years in the data series:
Why do levels change across the day? Although patterns vary considerably, levels normally rise overnight as the top of the atmospheric boundary layer is closer to the ground. At daybreak, the boundary layer rises and winds bring in ‘cleaner’ air from higher levels, while photosynthesis also reduces carbon dioxide levels, until the sun goes down.
Learning about traffic-related emissions in Brisbane
Average levels measured at Petrie Terrace for weekdays were higher than for weekends in the morning and afternoon/evening commuting times, but lower in the early morning hours. Differences in traffic emissions are the likely explanation. (Note: some missing days during 2023). Strong similarities with data using much more sophisticated measurements, from Mexico City and Munich (below) including the reversal from early morning to the afternoon and evening. (González del Castillo, E. et al. (2022) ‘CO2 variability in the Mexico City region from in situ measurements at an urban and a background site’, Atmósfera, 35(2), pp. 377–393. Available at: https://doi.org/10.20937/atm.52956.) & Lan, L. et al. (2020) ‘Assessment of Urban CO2 Measurement and Source Attribution in Munich Based on TDLAS-WMS and Trajectory Analysis’, Atmosphere, 11(1), p. 58. Available at: https://doi.org/10.3390/atmos11010058.).
Another way of viewing this is to subtract weekend values from weekday values. This shows the morning and afternoon/evening commuting time peaks very clearly.
Why do weekdays have lower values than weekends in the early morning? Sunday ends low, which runs into Monday morning and brings down the weekday average for those early hours. Saturday ends high (perhaps because of late evening entertainment-related traffic), which runs into Sunday morning and elevates the weekend values in those hours.
The increment of 4-6 ppm for weekdays compared to weekends doesn’t indicate the total effect of traffic emissions as it is just a difference score – even on weekends the city centre has a high traffic load.
This analysis shows the value of targeted comparisons – even though our low-cost equipment limits the accuracy of measurements (and therefore inferences about data from different sites), comparisons made over the same time-period can be made with much greater confidence.
(Table presents latest data, which may include revisions based on periodic recalibration of equipment, correction of errors, omissions, etc.) Please note that data for Petrie Terrace between 21 Nov 2023 and 03 Jan 2024 will soon be revised in the next few days to account for drift in a sensor – now replaced).