the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Dec 2025
Modelling the deep convective transport of trace gases (CO, NH3 and SO2) from the planetary boundary layer to the Asian summer monsoon anticyclone
Abstract. Deep convection plays a vital role in transporting Asian pollutants from the planetary boundary layer (PBL) into the Asian summer monsoon anticyclone (ASMA). However, the efficiency and effectiveness of transporting pollutants with various chemical and physical properties to the ASMA remain unclear. In this study, we use the global atmospheric chemistry and climate model EMAC to investigate the deep convective transport of trace gases such as CO, NH3 and SO2 from the PBL to the ASMA over the years 2010–2020. We quantify the deep convective transport efficiency of different trace gases into the ASMA. We show that the strongest convective transport tendency occurs over northern India and the southern edge of the Tibetan Plateau for CO (0.2–0.5 ppbv hr-1), over the south and eastern parts of the Tibetan Plateau for NH3 (0.02–0.05 ppbv hr-1), and over central India and eastern China for SO2 (0.002–0.005 ppbv hr-1). We find that, in contrast to CO and NH3, the SO2 enhancements within the ASMA are very weak, and there is can even be a decrease in SO2 over the southern Tibetan Plateau relative to the surroundings. Our analysis indicates that gas-liquid partitioning in clouds and subsequent wet deposition over South Asia are more effective at reducing SO2 than NH3 reaching the Tibetan Plateau and the ASMA. In view of ongoing changes in regional emissions, the effects of deep convective transport of various pollutants and associated gas-aerosol-cloud interactions on the chemical features of the ASMA require continued investigation.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-5587', Anonymous Referee #1, 21 Jan 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-5587/egusphere-2025-5587-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2025-5587-RC1 - AC1: 'Reply on RC1', Jianzhong Ma, 29 Jan 2026
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RC2: 'Comment on egusphere-2025-5587', Anonymous Referee #2, 16 Feb 2026
Review of “Modelling the deep convective transport of trace gases (CO, NH3 and SO2) from the planetary boundary layer to the Asian summer monsoon anticyclone” by J. Ma et al.
This study uses the EMAC chemistry–climate model to diagnose deep-convective transport of CO, NH₃, and SO₂ from the planetary boundary layer (PBL) into the Asian summer monsoon anticyclone (ASMA) during JJA for 2010–2020, and interprets inter-species differences using convective cloud partitioning and wet deposition diagnostics.
The topic is relevant and potentially informative. However, key conclusions are not sufficiently supported because (i) the diagnostics are interpreted beyond what they can uniquely demonstrate, and (ii) the manuscript lacks an observational evaluation of the modelled convection and UTLS tracer distributions that underpin the results.
Overall assessment / recommendation
Major revision. The current evidence is not yet sufficient to substantiate the stronger claims about the “dominant role” of deep convection and tracer-specific pathways into the ASMA, especially given the reliance on seasonal averages, the lack of explicit budget attribution (e.g., horizontal advection vs convective injection), and the potential influence of non-PBL SO₂ sources.
Major comments
- The manuscript makes a broad novelty statement (“for the first time… quantify the deep convective transport efficiency…”). As written, this is too broad, as convective “efficiency” metrics and convective injection diagnostics are used in the broader convection–chemistry literature. The paper does not clearly delineate what is new (e.g., the specific CVTRANS/UMF framework applied to a multi-year ASMA climatology for these tracers), versus an application of existing diagnostics.
- The convective transport tendency (CVT) is defined as the difference in mixing ratio before and after the CVTRANS step, isolating the convective effect. However, the manuscript states that the mean CVT is calculated by averaging across all time intervals, not only deep convection events. But a time-mean over all intervals blends convective and non-convective periods and is not equivalent to a convective-conditional tendency. Yet the Results/Discussion uses correspondence between CVT and seasonal-mean mixing ratios to argue a “dominant role” of deep convection. This inference is not robust without explicitly demonstrating the relative roles of other processes that shape ASMA composition (horizontal advection/recirculation in the anticyclone, large-scale ascent, mixing, chemical loss, wet scavenging). This is particularly important for CO, which is long-lived and readily redistributed horizontally after injection.
- The model configuration includes explosive volcanic SO₂ plumes during 2010–2020, added to the UTLS background SO₂. Because the central goal is PBL to ASMA convective transport, this introduces a significant attribution ambiguity on the UTLS/ASMA SO₂ burden. The diagnostics (including CVE/CVT interpretations) presented here may not reflect boundary-layer Asian emissions alone. The manuscript notes this issue only briefly, but it directly affects the interpretability of SO₂ spatial patterns and transport conclusions.
- The manuscript references prior evaluations of EMAC but does not provide a focused evaluation of the modelled deep convection frequency and vertical reach in JJA over the ASMA region, and UTLS distributions of CO, NH₃, and SO₂ during the study period with observations. Given that the paper’s conclusions hinge on convection and scavenging processes, this absence weakens confidence in the interpretation.
Minor/technical comments
- In the abstract, “there is can even be a decrease…” needs correction
- There appears to be a latitude typo (20–40°N) and a pressure-unit typo (100 hPa) in lines 6-7.
- CVT is defined as a before/after CVTRANS mixing ratio difference, but the reported tendency units (ppbv hr⁻¹) require explicit time normalization; this step is not clearly stated in the methodology description.
- In the introduction, “a convective manifestation observed…” is a vague term; it should be revised.
- Figure 1 caption; correct “overlayed” to “overlaid.
- In section 3.2, correct the unit “pptbv”
- What do you mean by “in the rains” in figure 7 caption?
Citation: https://doi.org/10.5194/egusphere-2025-5587-RC2
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