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arxiv: 1907.10007 · v1 · pith:ZBWWN6M3new · submitted 2019-07-23 · ⚛️ physics.ao-ph · physics.geo-ph

Ground/space, passive/active remote sensing observations coupled with particle dispersion modelling to understand the inter-continental transport of wildfire smoke plumes

Pith reviewed 2026-05-24 17:01 UTC · model grok-4.3

classification ⚛️ physics.ao-ph physics.geo-ph
keywords wildfire smokeintercontinental transportlidar observationsaerosol optical depthCALIOPAERONETIberian Peninsulaparticle dispersion modeling
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The pith

Wildfire smoke from the Pacific Northwest reached the Iberian Peninsula on 7-8 September 2017, arriving in the troposphere with altitude-specific optical properties.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tracks smoke from intense September 2017 fires in British Columbia, Alberta, Washington, Oregon, Idaho, Montana and northern California using satellite imagery to locate two main clouds, AERONET measurements at Spanish sites showing aerosol optical depth up to 0.62 with fine-mode fraction above 0.88 and single-scattering albedo above 0.98, CALIOP profiles indicating stratospheric presence during transit, and ground lidars revealing depolarization ratios of 0.05-0.10 and color ratios of 2.5-3.0 once over the Iberian Peninsula. Particle dispersion modeling links the layers to the source fires. A sympathetic reader would care because the work shows how distant fires can deliver measurable aerosols to populated regions within days, with clear differences between mid-tropospheric and upper-tropospheric layers.

Core claim

Satellite imagery and particle dispersion modeling identify two smoke clouds from the 2017 Pacific Northwest wildfires that reached the Iberian Peninsula on 7 and 8 September. AERONET data at mid-altitude sites record high fine-mode dominance and low absorption. CALIOP shows smoke in the stratosphere during transport but only in the troposphere at arrival. Ground-based lidars from EARLINET/ACTRIS and MPLNET detect distinct layers: depolarization ratio 0.05 and color ratio 2.5 at 5-9 km versus 0.10 and 3.0 at 10-13 km, with the color ratio increasing over time in the mid-troposphere.

What carries the argument

Coupled passive and active remote sensing (satellite imagery, AERONET columnar retrievals, CALIOP spaceborne lidar, ground-based lidars) with particle dispersion modeling to trace and characterize intercontinental smoke transport at multiple altitudes.

If this is right

  • Smoke particles can remain suspended and detectable after crossing the Atlantic in a few days.
  • Stratospheric injection occurs during transport while arrival occurs only in the troposphere.
  • Mid-tropospheric layers maintain stable depolarization while color ratio rises, consistent with faster sedimentation of larger particles.
  • Fine-mode particles dominate the transported plume and produce high single-scattering albedo.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Routine integration of ground and space lidars with dispersion models could shorten the time needed to attribute distant aerosol events to specific sources.
  • Altitude-dependent changes observed here suggest that sedimentation and aging processes during long-range transport should be tested in global aerosol models.
  • The event supplies a natural experiment for checking how well current networks capture the vertical structure of smoke arriving from other continents.

Load-bearing premise

The aerosol layers detected over Spain are assumed to have come from the specific 2017 wildfires in the listed North American regions.

What would settle it

If back-trajectory calculations or chemical tracer analysis showed the observed layers over the Iberian Peninsula did not connect to the September 2017 Pacific Northwest fires, the transport attribution would fail.

Figures

Figures reproduced from arXiv: 1907.10007 by A. Comeron, A. del Aguila, A.E. Bedoya-Velasquez, A. J. Fernandez, A. Rodriguez-Gomez, C. Cordoba-Jabonero, C. Munoz-Porcar, D. Bortoli, F. Molero, F. Rocadenbosch, J.A. Benavent-Oltra, J.L. Guerrero-Rascado, L. Alados-Arboledas, M. J. Costa, M. J. Granados-Munoz, M. Potes, M. Pujadas, M. Sicard, M. Yela, N. Papagiannopoulos, O. Jorba, P. Ortiz-Amezcua, R. Barragan, R. Roman, R. Salgado, V. Salgueiro, Y. Sola.

Figure 1
Figure 1. Figure 1: MODIS/Aqua corrected reflectance (true color) map centered over Spain on 8 September. Green bullets indicate lidar stations (EV: Évora, AR: El Arenosillo/Huelva, GR: Granada, MA: Madrid, BA: Barcelona) and red bullets indicate AERONET sites. Map created from https://firms.modaps.eosdis.nasa.gov/map/. MA EV AR GR BA Montsec Cerro Poyos [PITH_FULL_IMAGE:figures/full_fig_p011_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Flowchart of the methodology. 4 Canadian/United States fires and general overview The first hint of the arrival and the presence of the smoke plume over the IP is given by the temporal evolution of a combination of AERONET parameters in Montsec and Cerro Poyos, namely the AOD at 440 nm, AE440 870  , and FMF ( [PITH_FULL_IMAGE:figures/full_fig_p013_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: AOD440 (black), FMF (blue) and AE440-870 (red) in (top) Montsec, northeastern Spain, and (bottom) Cerro Poyos, south Spain. The gray areas in the bars on top of the figures indicate coincident lidar measurements. smoke particles (diameter > 1μm). In Cerro Poyos, the background AOD at 440 nm is even lower than in Montsec, being smaller than 0.1 (AERONET, 2018). This value is exceeded from 5 September on, an… view at source ↗
Figure 4
Figure 4. Figure 4: Total column carbon monoxide (day/night) from AIRS/AQUA from 30 August until 8 September. The extra plot at the bottom to the right represents the MODIS combined (Aqua and Terra) value-added AOD at 550 nm on 8 September. The red star indicates the position of the active fires. On the plots of 3 and 4 September the descending, nighttime orbits of CALIPSO are reported. Maps created from https://worldview.ear… view at source ↗
Figure 5
Figure 5. Figure 5: (top) 10-day back-trajectories, 1-hour resolution, arriving in Madrid, in the center of Spain, on 8 September at 00UT at heights of 3 (red), 6 (green) and 11 (blue) km; (bottom) Same back-trajectories, different viewing angle and superposition of CALIOP curtains on 4 September at 05:10UT (D-4, day-4 before arrival) and on 3 September at 09:23UT (D-5) where the smoke plumes, clearly visible, match very well… view at source ↗
Figure 6
Figure 6. Figure 6: AERONET daily mean spectral (top) AAOD, (center) SSA, and (bottom) asymmetry factor at Montsec and Cerro Poyos on 7 and 8 September. SSA were due to low BC emission at the source, the following rationale can be made. According to Radke et al. (1991) and more recently to Russell et al. (2014) the absorption properties of biomass burning in its smoldering combustion phase are lower than during its flaming ph… view at source ↗
Figure 7
Figure 7. Figure 7: Nighttime multi-wavelength lidar inversion in Évora on 7 September between 04 and 06UT. The first plot represents the quicklook of range-square corrected signal at 1064 nm in arbitrary units.  is the particle backscatter coefficient,  the particle extinction coefficient,   AE the extinction-related AE, CR the color ratio, LR the lidar ratio and  p the particle depolarization ratio. Mean values in the … view at source ↗
Figure 8
Figure 8. Figure 8: CALIOP images and products on (left) 4 September at 05:10UT (D-4, Plume 1 released 5 days earlier) and (right) 3 September at 09:23UT (D-5, Plume 2, fresh < 1 day). (top) CALIOP quicklooks of the total attenuated backscatter signal at 532 nm; (center) CALIOP quicklooks of the retrieved backscatter coefficient at 532 nm restricted to the smoke plume (red squares); (bottom) CALIOP mean profiles of backscatte… view at source ↗
Figure 9
Figure 9. Figure 9: (top) Mid and upper tropospheric layer mean particle depolarization ratios at 532 nm at all Iberian lidar stations on the night of 7 to 8 September. Cyan and Purple bullets represent CALIOP measurements. The vertical bars indicate the vertical extension of the smoke layers of maximum intensity (base to top height). The horizontal bars indicate the standard deviation associated to  p in these layers. (bott… view at source ↗
Figure 10
Figure 10. Figure 10: (top) Dispersion map of CO column density and longitudinal cross-section of CO concentration at the latitude of Madrid on 8 September at 00UT; (center) the same for BC; (bottom) the same of OC. Note the different scales. The emission and dispersion 0 1 2 3 0 5 10 15  (Mm-1 sr-1 ) CO concentration ( g m-3) CO, P1 CO, P2 , lidar 0123 Tropopause = 12.6 km 0 4 8 12 0 5 10 15  (Mm-1 sr-1 ) BC concentration… view at source ↗
Figure 1
Figure 1. Figure 1: MODIS/Aqua corrected reflectance (true color) map centered over Spain on 8 September. Green bullets [PITH_FULL_IMAGE:figures/full_fig_p050_1.png] view at source ↗
Figure 6
Figure 6. Figure 6: AERONET daily mean spectral (top) AAOD, (center) SS [PITH_FULL_IMAGE:figures/full_fig_p050_6.png] view at source ↗
Figure 8
Figure 8. Figure 8: CALIOP images and products on (left) 4 September at 05:10UT (D-4, Plume 1 released 5 days earlier) and [PITH_FULL_IMAGE:figures/full_fig_p050_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: (top) Mid and upper tropospheric layer mean particle depolarization ratios at 532 nm at all Iberian lidar [PITH_FULL_IMAGE:figures/full_fig_p051_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: (top) Dispersion map of CO column density and longitudinal cross-section of CO concentration at the [PITH_FULL_IMAGE:figures/full_fig_p051_10.png] view at source ↗
read the original abstract

During the 2017 record-breaking burning season in Canada / United States, intense wild fires raged during the first week of September in the Pacific northwestern region (British Columbia, Alberta, Washington, Oregon, Idaho, Montana and northern California) burning mostly temperate coniferous forests. The heavy loads of smoke particles emitted in the atmosphere reached the Iberian Peninsula (IP) a few days later on 7 and 8 September. Satellite imagery allows to identify two main smoke clouds emitted during two different periods that were injected and transported in the atmosphere at several altitude levels. Columnar properties on 7 and 8 September at two Aerosol Robotic Network (AERONET) mid-altitude, background sites in northern and southern Spain are: aerosol optical depth (AOD) at 440 nm up to 0.62, Angstrom exponent of 1.6-1.7, large dominance of small particles (fine mode fraction > 0.88), low absorption AOD at 440 nm (<0.008) and large single scattering albedo at 440 nm (>0.98). Profiles from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) show the presence of smoke particles in the stratosphere during the transport, whereas the smoke is only observed in the troposphere at its arrival over the IP. Portuguese and Spanish ground lidar stations from the European Aerosol Research Lidar Network / Aerosols, Clouds, and Trace gases Research InfraStructure Network (EARLINET/ACTRIS) and the Micro-Pulse Lidar NETwork (MPLNET) reveal smoke plumes with different properties: particle depolarization ratio and color ratio, respectively, of 0.05 and 2.5 in the mid troposphere (5-9 km) and of 0.10 and 3.0 in the upper troposphere (10-13 km). In the mid troposphere the particle depolarization ratio does not seem time-dependent during the transport whereas the color ratio seems to increase (larger particles sediment first).

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript uses satellite imagery, AERONET columnar aerosol data (AOD440 up to 0.62, fine-mode fraction >0.88, SSA >0.98), CALIOP profiles, and ground-based lidar measurements from EARLINET/ACTRIS and MPLNET (depolarization ratios 0.05–0.10, color ratios 2.5–3.0) together with particle dispersion modeling to attribute distinct smoke layers observed over the Iberian Peninsula on 7–8 September 2017 to the early-September Pacific Northwest wildfires. It distinguishes stratospheric transport from tropospheric arrival and reports altitude-dependent optical properties consistent with aged smoke.

Significance. If the source attribution holds, the work demonstrates the value of coordinated multi-platform remote-sensing networks for tracking intercontinental wildfire smoke transport and characterizing vertical structure and aging signatures. The quantitative multi-instrument dataset provides a useful benchmark for aerosol transport and sedimentation models.

major comments (2)
  1. [modeling description] The central attribution of the observed layers to the specified North American wildfires rests on particle dispersion modeling, yet the manuscript provides no details on the model employed, its configuration, emission source data, or any sensitivity/arrival-time validation against the 7–8 September observations (modeling paragraph and abstract).
  2. [lidar results] The reported differences in lidar properties between the mid-troposphere (depolarization 0.05, color ratio 2.5) and upper troposphere (0.10, 3.0) are presented as evidence of differential sedimentation, but without stated uncertainties, vertical resolution, or temporal sampling statistics it is unclear whether the differences exceed measurement variability (lidar results section).
minor comments (2)
  1. [abstract] The abstract states that smoke is observed in the stratosphere during transport but only in the troposphere upon arrival; a brief sentence clarifying the physical mechanism or observational basis for this transition would improve clarity.
  2. [AERONET section] AERONET site names and exact coordinates for the northern and southern Spanish stations are not given; adding them would aid reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive assessment and constructive comments, which help strengthen the manuscript. We address each major comment below.

read point-by-point responses
  1. Referee: [modeling description] The central attribution of the observed layers to the specified North American wildfires rests on particle dispersion modeling, yet the manuscript provides no details on the model employed, its configuration, emission source data, or any sensitivity/arrival-time validation against the 7–8 September observations (modeling paragraph and abstract).

    Authors: We agree that the manuscript does not provide sufficient details on the particle dispersion modeling. In the revised version we will add a dedicated paragraph (or subsection) describing the specific model used, its configuration and setup, the wildfire emission inventories employed, and any sensitivity tests or direct comparison of modeled arrival times with the 7–8 September observations over the Iberian Peninsula. revision: yes

  2. Referee: [lidar results] The reported differences in lidar properties between the mid-troposphere (depolarization 0.05, color ratio 2.5) and upper troposphere (0.10, 3.0) are presented as evidence of differential sedimentation, but without stated uncertainties, vertical resolution, or temporal sampling statistics it is unclear whether the differences exceed measurement variability (lidar results section).

    Authors: We acknowledge that the lidar results section would benefit from explicit reporting of measurement uncertainties, vertical resolution, and temporal sampling statistics. In the revision we will add these quantities (derived from the EARLINET/ACTRIS and MPLNET instrument specifications and data processing) together with a brief assessment of whether the observed differences in depolarization ratio and color ratio exceed the combined variability. revision: yes

Circularity Check

0 steps flagged

No significant circularity; purely observational attribution

full rationale

The paper presents a multi-instrument observational analysis of aerosol properties (AERONET AOD, CALIOP profiles, EARLINET/MPLNET lidar depolarization and color ratios) combined with satellite imagery and particle dispersion modeling for source attribution of the 2017 wildfire smoke. No equations, fitted parameters, derivations, or self-citations appear in the provided text that reduce any claim to its own inputs by construction. The attribution step relies on independent external modeling and imagery rather than internal fitting or self-referential logic, rendering the chain self-contained.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Observational case study with no free parameters, no new entities, and only standard domain assumptions about lidar interpretation.

axioms (1)
  • domain assumption Standard interpretation of lidar depolarization ratio and color ratio as indicators of particle shape and size for smoke aerosols
    Invoked when assigning different properties to mid-troposphere versus upper-troposphere layers.

pith-pipeline@v0.9.0 · 6076 in / 1240 out tokens · 26469 ms · 2026-05-24T17:01:18.408596+00:00 · methodology

discussion (0)

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