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arxiv: 2503.11803 · v6 · pith:LBLAWCSRnew · submitted 2025-03-14 · ⚛️ physics.flu-dyn · cond-mat.mtrl-sci· physics.ao-ph

Harnessing natural and mechanical airflows for surface-based atmospheric pollutant removal

Samuel D. Tomlinson , Aliki M. Tsopelakou , Tzia M. Onn , Steven R. H. Barrett , Adam M. Boies , Shaun D. Fitzgerald This is my paper

Pith reviewed 2026-05-22 23:50 UTC · model grok-4.3

classification ⚛️ physics.flu-dyn cond-mat.mtrl-sciphysics.ao-ph
keywords surface-based removalatmospheric flow ratesHVAC filtersCO2 sorptionCH4 catalystpollutant transportclimate mitigation costsbuilt environment airflows
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The pith

HVAC filters could remove CO2 at costs as low as $600 per tonne if sorption materials are added to their surfaces.

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

The paper quantifies how much air flows naturally or mechanically across surfaces in cities, solar farms, and ventilation systems, then applies literature removal efficiencies to estimate global pollutant capture potential. Cities alone move 30 Gt of CO2 per year across their surfaces, enough that scaled technologies could exceed 1 GtCO2 removed annually. The work shows HVAC systems offer the lowest estimated cost because their forced airflows concentrate contact on replaceable filter surfaces, reaching $600 per tonne of CO2 versus $3000 for city surfaces. These upper-bound calculations rest on the assumption that lab-scale performance can be maintained across entire infrastructure areas through routine replacement.

Core claim

Atmospheric flow rates to urban surfaces, solar farms, and HVAC systems are large enough that surface-based CO2-sorption and CH4-catalyst technologies, if applied at literature efficiencies across total surface area and maintained by replacement, could remove more than 1 GtCO2 per year, with HVAC filters achieving the lowest costs of $600 per tCO2 ($2000 per tCO2e) compared with $3000 per tCO2 for city surfaces.

What carries the argument

Transport-limited removal potential calculated from measured or modeled annual atmospheric flow rates to total surface area of each configuration, multiplied by literature removal efficiencies per unit area.

If this is right

  • Cities move a median 30 GtCO2, 0.06 GtCH4, 0.007 GtNOx and 0.0001 GtPM2.5 per year across their surfaces.
  • HVAC systems, cities and solar farms each have flow rates sufficient for >1 GtCO2/y removal if lab efficiencies hold.
  • Incorporating CO2-sorption or CH4-catalyst materials into HVAC filters yields the lowest cost per tonne among the configurations examined.
  • Routine filter replacement is required to keep removal performance at the levels used for the cost estimates.

Where Pith is reading between the lines

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

  • If real-world scaling works, the approach could be integrated into existing building codes and solar-farm maintenance schedules without new land use.
  • The cost advantage of HVAC would widen further if filter replacement cycles can be aligned with normal building servicing rather than added as a separate expense.
  • A next step would be to measure actual capture rates on operating HVAC units to test whether the transport-limited bound is reachable.

Load-bearing premise

Laboratory removal efficiencies can be applied to the full surface area of cities, solar farms, and HVAC systems without major loss while performance is kept up by routine replacement.

What would settle it

A large-scale field measurement on an actual building HVAC system or city block showing sustained removal rates per square meter fall more than 50 percent below the lab values used in the cost model.

Figures

Figures reproduced from arXiv: 2503.11803 by Adam M. Boies, Aliki M. Tsopelakou, Samuel D. Tomlinson, Shaun D. Fitzgerald, Steven R. H. Barrett, Tzia M. Onn.

Figure 1
Figure 1. Figure 1: Flow rates through global environments. (A) Streamwise [PITH_FULL_IMAGE:figures/full_fig_p011_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Atmospheric pollutant fluxes to the surfaces of global en [PITH_FULL_IMAGE:figures/full_fig_p013_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Atmospheric pollutant flow rates to the surfaces of globa [PITH_FULL_IMAGE:figures/full_fig_p015_3.png] view at source ↗
read the original abstract

Removal strategies for atmospheric pollutants are increasingly being considered to mitigate global warming and improve public health. However, the global potential of surface-based removal techniques has not yet been quantified based on limits of pollutant transport and removal rates. We evaluate the atmospheric pollutant transport to surfaces and assess the potential of surface-based removal technologies for global-scale deployment across a variety of configurations, including air interaction with the built environment, mechanical ventilation and convection systems, and over the global transportation fleet. Cities provide the highest transport-limited removal potential, with median annual atmospheric flow rates of 30 GtCO$_2$, 0.06 GtCH$_4$, 0.007 GtNO$_\text{x}$ and 0.0001 GtPM$_{2.5}$ to their total surface area. Cities, solar farms and HVAC systems have flow rates large enough to potentially remove more than 1 GtCO$_2$/y (1 GtCO$_2$e/y for CH$_4$, 20-year GWP), if laboratory-scale removal efficiencies from the literature are applied to their total surface area, however, achieving this would require technological advances. Based on their transport-limited upper bounds, HVAC filters have the potential to achieve costs as low as \$600 per tCO$_2$ removed (\$2000 per tCO$_2$e) if CO$_2$-sorption (CH$_4$-catalyst) technologies are incorporated into their surfaces and performance is maintained through routine replacement, compared with \$3000 per tCO$_2$ (\$10000 per tCO$_2$e) for city surfaces, using literature values for these technologies' material and application costs. These findings demonstrate that integrating surface-based pollutant removal technologies into infrastructure may offer a pathway to advance climate objectives, though further studies are needed to assess their feasibility in application, and application-implementation rates and cost.

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 / 1 minor

Summary. The manuscript calculates transport-limited flow rates of CO2, CH4, NOx and PM2.5 to surfaces including cities (median 30 GtCO2/y), solar farms, HVAC systems and the global transportation fleet. Applying literature lab-scale removal efficiencies to these full surface areas yields potentials exceeding 1 GtCO2/y (or 1 GtCO2e/y for CH4) for several configurations, with derived costs of $600/tCO2 ($2000/tCO2e) for HVAC filters incorporating sorption/catalyst technologies versus $3000/tCO2 ($10000/tCO2e) for city surfaces, assuming routine replacement maintains performance.

Significance. The transport-limited upper-bound framework is a clear strength and could usefully bound the scale of surface-based removal if the scaling assumptions are later validated. The cost comparison between HVAC and city surfaces, if substantiated, would highlight infrastructure integration as a potentially lower-cost route than diffuse urban surfaces. However, the quantitative claims rest entirely on untested extrapolation of lab efficiencies, limiting immediate policy or engineering relevance.

major comments (2)
  1. [Abstract] Abstract: the HVAC cost claim of $600 per tCO2 removed is obtained by multiplying transport-limited flow rates by literature lab-scale removal efficiencies and dividing by material/application costs. No section quantifies or bounds the reduction in effective efficiency that would arise from boundary-layer resistance, flow maldistribution across heterogeneous km-scale surfaces, or long-term sorbent deactivation; this direct extrapolation is load-bearing for the reported cost advantage over city surfaces.
  2. [Abstract] Abstract and results discussion: the removal potentials (>1 GtCO2/y) and all cost figures are presented without error bars, sensitivity analysis on the lab efficiencies, or discussion of scaling losses, despite the text acknowledging that technological advances are required. The absence of these elements makes the central numerical claims unverifiable from the given information.
minor comments (1)
  1. [Abstract] Abstract: subscript notation for NOx (NO$ _text{x} $) and PM2.5 is inconsistent with standard inline math; a uniform typesetting convention would improve readability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their review. Our manuscript provides transport-limited upper bounds on removal potentials by applying literature lab efficiencies to calculated surface flows, with explicit caveats that technological advances are needed. We respond to the major comments below.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the HVAC cost claim of $600 per tCO2 removed is obtained by multiplying transport-limited flow rates by literature lab-scale removal efficiencies and dividing by material/application costs. No section quantifies or bounds the reduction in effective efficiency that would arise from boundary-layer resistance, flow maldistribution across heterogeneous km-scale surfaces, or long-term sorbent deactivation; this direct extrapolation is load-bearing for the reported cost advantage over city surfaces.

    Authors: We agree the cost figures assume lab efficiencies can be maintained at full scale without the cited losses. The analysis is presented as an optimistic upper bound conditional on achieving those efficiencies, as noted in the text. We will revise the abstract and add a discussion paragraph explicitly addressing how boundary-layer resistance, maldistribution, and deactivation could reduce effective rates and alter the HVAC-city cost comparison, while preserving the transport-limited framework. Precise quantification of these reductions requires additional modeling beyond the current scope. revision: partial

  2. Referee: [Abstract] Abstract and results discussion: the removal potentials (>1 GtCO2/y) and all cost figures are presented without error bars, sensitivity analysis on the lab efficiencies, or discussion of scaling losses, despite the text acknowledging that technological advances are required. The absence of these elements makes the central numerical claims unverifiable from the given information.

    Authors: The numerical values use point estimates from the cited literature applied to the transport flows. To enhance verifiability we will add a sensitivity analysis in the results section, showing how potentials and costs change under reduced effective efficiencies (e.g., 10-100% of lab values) to illustrate scaling losses and the impact of required technological advances. This will be referenced in the abstract and discussion. Error bars are omitted because the source studies report point values without uncertainties. revision: yes

Circularity Check

0 steps flagged

No circularity: cost and removal potentials derived from external literature values applied to independently calculated transport flows.

full rationale

The paper calculates transport-limited flow rates to surfaces using atmospheric data and surface areas, then multiplies by removal efficiencies and divides by material costs taken directly from external literature. No internal equations fit parameters to subsets of the paper's own results and rename them as predictions, no self-citations supply load-bearing uniqueness theorems or ansatzes, and no derivation reduces by construction to its inputs. The scalability assumption (lab efficiencies to city/HVAC scales) is an external modeling choice, not a circular reduction.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The analysis depends on external literature values for removal efficiencies and costs plus domain assumptions about uniform application of lab results to large surfaces and maintenance through replacement; no new entities are postulated.

free parameters (2)
  • lab-scale removal efficiencies
    Taken directly from literature and applied to total surface areas without scale adjustment
  • material and application costs
    Taken from literature values for sorption and catalyst technologies
axioms (2)
  • domain assumption Atmospheric flow rates to surfaces can be represented by the stated median annual values for each configuration
    Used to set transport-limited upper bounds on removal
  • domain assumption Performance of incorporated technologies can be maintained through routine replacement
    Required for the HVAC cost calculation

pith-pipeline@v0.9.0 · 5909 in / 1354 out tokens · 60559 ms · 2026-05-22T23:50:24.385199+00:00 · methodology

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Forward citations

Cited by 1 Pith paper

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Reference graph

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