| 04 Feb 2026
Evidence for the impact of fire activity on daily variations of IASI mid-tropospheric CO2 anomalies at 8–11 km
Abstract. Biomass burning is a major, highly variable source of atmospheric CO2, but its impact on the free troposphere remains difficult to quantify because of uncertainties in injection heights and transport. In the tropics, intense fires can trigger pyroconvective plumes that loft combustion products to the mid- and upper troposphere. However, most fire emission inventories and global CO2 inversions still assume simplified vertical distributions of CO2 emitted by fires. Weighted columns of CO2 retrieved from remote sensing instruments that are sensitive to such high-altitude enhancements can inform of such dynamics. Here we combine mid-tropospheric CO2 (MT-CO2) retrievals from three IASI instruments with GOES-16 observations of Fire Radiative Energy (FRE) to link daily MT-CO2 anomalies observed by IASI at 8–11 km altitude to South American fire activity during the 2020 burning season, while accounting for long-range horizontal transport of anomalies. From August–October 2020, about 66 % of the detected anomalies originate from long-range or unknown sources and are discarded. For the remaining anomalies attributed to local fires, 72 h back trajectories do intersect with at least one active fire for 75 % of them. Their daily sum co-varies strongly with FRE, with the ratio between the two depending on the dominant horizontal transport regime. A comparison with CAMS IASI-weighted CO2 fields shows that model fails to reproduce both the amplitude and structure of the observed anomalies. Overall, our results demonstrate that IASI MT-CO2 anomalies carry an observational fingerprint of tropical fire activity.
The authors have combined satellite-derived measurements of CO2 concentrations for the mid troposphere with information on fire radiative energy (FRE) from fires from geostationary satellites. The anomalies in the CO2 concentrations are then linked to fire observations via backtrajectories and they show that circulation pattern strongly impact the degree to which the two are linked, and the CO2 to FRE ratio. A key conclusion is that pyroconvection is a crucial process and that this should be included in atmospheric models. I found this a novel and interesting piece of work that could pave the way for future studies that go a step further, for example estimating CO2 emissions per FRE or quantifying injection heights.
Comments:
L90-96: These kind of assumptions need to be made, but it would be nice to have a sensitivity analysis where you show how your results vary, had you made different assumptions. For example, the fire season is very extensive in this region and not confined to a fire plume here and there. Do the "background fires" also lead to anomalies or only the ones that are larger than those “regular” fires burning during the season? I ask this because it will be mostly the larger ones that have pyroconvection and thus relevant for your work. It is worthwhile to know whether those are the norm or the exception.
L219: Given that you more or less know when CO2-concentrations were enhanced and what the atmospheric transport was, are you able to more closely match anomalies with actual active fire detections (with some uncertainty)? So instead of investigating whether the backtrajectory intersected with fire detections, actually say with which fire detections? And would the match then still be 75% (line 278)? This could be relevant for follow-up work that could take advantage of linking vegetation types with plumes for example, or understanding how pyroconvection changes over the time of day etc.
L179: 1 degree is very coarse and there are higher spatial resolution wind fields available. I am not sure whether that could be used, but it would improve the quality of the study
L184: how about points north of 35N?
L314: for this period you note that the CO2:FRE ratio is very high, partly due to recirculation. I don’t fully understand why these periods still show up as anomalies; they are not lofted anymore due to pyroconvection and CO2-concentrations become more uniform probably. Just curious.
L369: “However, the amplitude of the atmospheric response is not determined by FRE magnitude alone, but also by fuel type, size, density, moisture content, and local meteorology” I feel this is crucial and would appreciate more text on what can be done in the future and how for example studies focusing on CO and CO2 can be merged here to improve our understanding of fires, their emissions, and their fate in the atmosphere.
Other
L16: If “active fire” refers to FRP observations then “active fire detection” may be better
L23: Ipcc -> IPCC
L25: A reference would be good here
L27-29: report everything just in Pg C may be easier
L35: Langenfelds (2002, GBC) may be a classic paper to cite about IAV of fire and CO2 growth rates
L35: “has used satellite observations to track fire-emitted” looks a word is missing in the end
L67: Not everybody may know where the Pantanal is, might be good to add a few words here
L81: Looks a . (dot) is missing between 2023) and CO2
L100: biomass burnings -> biomass burning regions
L102: values -> anomalies
L148: not clear what you mean with “maps”. Guess something like “emission fields’ would be easier to understand
Figure 3 would benefit from higher dpi
L198: 5x5 -> cross symbol
L291 and L299: anomaly -> anomalies
L298: Longitudinal -> longitudinal (guess in the whole section, also for Circular etc.)
Figure 6 would also benefit from higher dpi (or insert as .eps or .pdf?)
L357: Discussions - Discussion
L405: mandatory -> crucial