the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 May 2025
Atmospheric Dust and Air Quality over large-cities and megacities of the World
Abstract. Urbanization is accelerating, with over 55 % of the global population residing in urban areas as of 2018, projected to reach 60 % by 2030. This growth intensifies environmental pressures, notably air quality degradation, which adversely affects human health and socioeconomic systems. Among air pollutants, atmospheric mineral dust plays a critical role in Earth’s climate system and poses direct health risks. This study assesses the mass concentration of atmospheric dust within the planetary boundary layer (PBL)—the atmospheric region where most anthropogenic activity occurs—across global large cities and megacities (population >5 million). Using the European Space Agency’s LIdar climatology of Vertical Aerosol Structure (LIVAS) climate data record, which offers multiyear, four-dimensional Earth Observation-based dust mass concentration data, we analyze both fine-mode and coarse-mode dust components. Results show that current dust levels exceed World Health Organization (WHO) annual mean air quality guidelines (AQGs) for PM2.5 and PM10 in 49.4 % and 87.7 % of urban areas studied, respectively, exposing approximately 701.4 million people to hazardous dust concentrations. Regions particularly affected include the Middle East, Indian subcontinent, East Asia, North Africa, and the Sahel. Projections indicate a 21.7 % increase in the exposed population by 2030, totaling 856.5 million, despite a general decline in dust severity in over 70 % of cities. Epidemiological models are employed to estimate associated health risks. This work provides essential insights for evidence-based air quality management and public health strategies, supporting mitigation efforts in the face of urban expansion and climate change.
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RC1: 'Comment on egusphere-2025-1841', Anonymous Referee #4, 01 Jul 2025
This is a generally well-written paper on an important topic. I have only a few relatively minor suggested revisions.
The text is somewhat wordy. It would benefit from a read-through to streamline and eliminate redundancies. For example, the beginning of Section 6 is redundant with the portion of Section 1 that describes the health impacts of coarse and fine particles.
Along the same lines, the portion of Section 1 that describes the importance of atmospheric dust in terms of its "effects on biogeochemistry, the radiation budget, weather, and climate" (lines 47-66) is too detailed. The study focuses on the health impacts of dust, so the importance of atmospheric dust's impacts on human health should be the focus. Briefly mentioning the important of dust in other fields would be sufficient.
The authors never address the fundamental question of why they used remote sensing data, i.e. CALIPSO and AERONET, to analyze the impacts of dust on surface air quality, instead of surface PM10 and PM2.5 monitors. Do the 81 cities analyzed have PM monitor networks? Were PM monitor data used to, for example, validate the ESA-LIVAS atmospheric dust products? Using surface monitor data would counteract the shortcomings of the remote sensing dataset, such as the impacts of clouds and the coarse 1° x 1° spatial resolution. I suspect I know the reasoning for the authors' focus on remote sensing data, but they need to clearly justify their choice in Section 1. This is a glaring omission that will puzzle any air quality experts reading the paper.
Citation: https://doi.org/10.5194/egusphere-2025-1841-RC1 -
RC2: 'Comment on egusphere-2025-1841', Anonymous Referee #3, 20 Jul 2025
The study assesses global urban exposure to fine- and coarse-mode mineral dust within the planetary boundary layer (PBL) using satellite-derived data from the ESA-LIVAS climatology (2006–2022). It quantifies dust mass concentrations, evaluates compliance with WHO air quality guidelines, and estimates associated health risks for populations in 81 major cities and megacities. Future projections suggest continued health threats from dust exposure, especially in Africa and Asia, despite some decreasing trends.
In general, the overall work is well supported and professionally prepared. However, I would like to bring here 4 points for additional discussion:
1) Attribution of dust concentration trends to regulatory measures lacks empirical support
While the study highlights observed decreasing trends in both fine- and coarse-mode dust mass concentrations over many urban areas, it simultaneously acknowledges that these trends are mostly not statistically significant. Nevertheless, the paper suggests that such reductions reflect the effectiveness of regulatory measures. This connection appears speculative in the absence of a causal analysis. To strengthen this point, it would be necessary to incorporate a policy impact assessment or time-series intervention analysis demonstrating how specific air quality policies temporally align with reductions in dust levels.
2) Inconsistencies between EO-based dust mass concentrations and ground-based observations
The paper relies heavily on EO-derived dust mass concentrations from the ESA-LIVAS CDR product. However, it does not provide a systematic validation or cross-comparison with in-situ measurements (e.g., ground-based PM10/PM2.5 data from air quality monitoring stations) in urban centers for any of the cities. This raises concerns about potential mismatches between satellite-derived values and actual exposure levels experienced at the surface, especially given known limitations of satellite products in resolving near-surface conditions over complex urban terrains. A discussion on these discrepancies, or at least quantitative uncertainty bounds, would improve the transparency and reliability of the results. Some of the projections for southern European cities including Madrid or Barcelona, which share quite common atmospheric phenomenology, display very contrasted PM2.5 dust concentrations, in one case unrealistically high, the other unbelievably low. In this line, current (2006-2022) dust values in PM-coarse and PM2.5 are not coincident with experimental values provided extensively in the literature.
3) Overgeneralization of future exposure projections without accounting for uncertainty
The projections of future dust exposure and population impacts are presented with a high degree of numerical precision (e.g., 509.7 million people affected, 113.1% increase), but the uncertainties associated with both future dust concentrations and demographic changes are not adequately discussed. This gives a false sense of certainty in the forecasts. The study would benefit from including scenario-based projections that reflect the range of plausible futures, particularly considering how climate change, land use, and urban development might alter dust emissions and transport.
4) Lack of consideration of non-dust PM sources in health risk estimations
The study attributes PM2.5 and PM-coarse related health risks in major cities exclusively to mineral dust exposure, using dust-specific mass concentrations derived from EO data. However, in many urban environments, anthropogenic PM sources (traffic, industry, biomass burning) dominate the PM burden. Without source apportionment or a method to disentangle dust from other PM components, the derived Relative Risk and Attributable Fraction metrics might overestimate the health impacts attributable to dust alone. Clarifying this distinction, or acknowledging the limitations of the approach, would improve the robustness of the health impact assessment.
For specific regional domains, important references for dust occurrence and air quality outcomes, PM composition data or health impacts are missing. Some examples for the southern European case are here:
- African dust contributions to mean ambient PM10 mass-levels across the Mediterranean Basin, by Querol et al. 2009
- Pey, J., Querol, X., Alastuey, A., Forastiere, F., and Stafoggia, M.: African dust outbreaks over the Mediterranean Basin during 2001–2011: PM10 concentrations, phenomenology and trends, and its relation with synoptic and mesoscale meteorology, Atmos. Chem. Phys., 13, 1395–1410, https://doi.org/10.5194/acp-13-1395-2013, 2013.
- African dust and air quality over Spain: Is it only dust that matters?, by Querol et al. 2019
- Stafoggia M, Zauli-Sajani S, Pey J, Samoli E, Alessandrini E, Basagaña X, Cernigliaro A, Chiusolo M, Demaria M, Díaz J, Faustini A, Katsouyanni K, Kelessis AG, Linares C, Marchesi S, Medina S, Pandolfi P, Pérez N, Querol X, Randi G, Ranzi A, Tobias A, Forastiere F; MED-PARTICLES Study Group. Desert Dust Outbreaks in Southern Europe: Contribution to Daily PM₁₀ Concentrations and Short-Term Associations with Mortality and Hospital Admissions. Environ Health Perspect. 2016 Apr;124(4):413-9. doi: 10.1289/ehp.1409164. Epub 2015 Jul 24. PMID: 26219103; PMCID: PMC4829979.
Citation: https://doi.org/10.5194/egusphere-2025-1841-RC2
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