the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Nov 2025
Comparative assessment of MEGAN v2.1 and v3.2 biogenic VOC emissions over the Qinghai-Tibet Plateau: implications for summertime surface ozone simulations
Abstract. Biogenic volatile organic compounds (BVOCs) constitute a significant precursor to tropospheric ozone (O3) over the Qinghai-Tibet Plateau (QTP), yet substantial uncertainties persist in BVOC emission inventories for this high-altitude region. This study employs the WRF/CMAQ model to systematically compare BVOC emissions between MEGAN v2.1 and v3.2 over the QTP, and their impacts on surface O3 simulations for August 2022. MEGAN v3.2 yields total BVOC emissions (127.96 Gg) 44 % lower than v2.1 (229.67 Gg), with isoprene emissions 1.7 times lower and monoterpenes 0.3 times higher. Spatially, the most pronounced differences occur in southeastern Tibet and the Hengduan Mountains. Indirect constraints using TROPOMI formaldehyde (HCHO) vertical column densities (VCDs) and OMI/MLS total-column ozone (TCO) reveal that CMAQ simulations with v3.2 BVOC emissions exhibit a marginally stronger correlation with satellite HCHO VCDs (r = 0.34 vs 0.32, p < 0.01), while the simulated TCO agree similarly with the OMI/MLS TCO. Simulations with both inventories indicate that incorporating BVOCs increase regional average MDA8 O3 concentrations by 2–3 %. However, in Lhasa, Xining, and certain cities within the Hengduan Mountains, increases reach 5–14 %. In southeastern Tibet, where NOx is extremely scarce, the response is negligible. Due to its elevated isoprene emissions, MEGAN v2.1 increases the MDA8 O3 concentrations by up to 19.61 % in the aforementioned cities—nearly twice those in v3.2. It is recommended that v3.2 be prioritized for air quality modelling in pristine alpine region. These findings provide valuable guidance for designing effective air quality management policies over the QTP.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-5579', Anonymous Referee #1, 23 Dec 2025
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RC2: 'Comment on egusphere-2025-5579', Anonymous Referee #2, 23 Feb 2026
Li et al. present a comparative assessment of biogenic VOC (BVOC) emissions derived from MEGAN v2.1 and v3.2 over the Qinghai-Tibet Plateau (QTP). The study compares total BVOCs emissions and indirectly evaluates the schemes against satellite-observed HCHO and tropospheric ozone using the WRF-CMAQ model. The authors’ focus on the pristine QTP region is unique because BVOC emissions and their impacts on atmospheric chemistry have received limited attention in this region. However, after a careful review, I find that the current analysis lacks the depth required for publication in Atmospheric Chemistry and Physics. While the topic is interesting, the scientific insights provided are limited, and the validation methods employed are not robust. Therefore, I regret that I cannot recommend this manuscript for publication in its current form. I hope the following specific comments will be helpful for the authors in refining their work for future submission.
Specific Comments
1. The study applies existing MEGAN versions without specific mechanical adaptations or tuning for the unique environment of the QTP. There is a lack of in-depth discussion regarding the dominant vegetation types contributing to emissions in this region and their specific responses to meteorological conditions. Furthermore, the comparison between the two schemes, focusing primarily on total emissions and spatial distribution, remains largely descriptive and does not provide any mechanistic explanation for the observed discrepancies. The study would benefit significantly from using more direct observations to rigorously pinpoint the strengths and weaknesses of each scheme.
2. The attempt to evaluate BVOC emission schemes through indirect comparison with satellite-observed HCHO and tropospheric ozone is methodologically unreasonable. Discrepancies between model simulations and satellite data can stem from numerous factors, particularly uncertainties in the model’s chemical mechanisms and transport processes. In the QTP, background ozone sources (e.g., stratospheric intrusion or long-range transport) play a critical role. Since BVOCs likely contribute only a small fraction to ozone formation in this region, using tropospheric ozone as a proxy to validate BVOC emission schemes is not a promising approach. Additionally, the manuscript does not clarify whether the satellite averaging kernels were applied when comparing the simulation results with observations, which is essential for a valid comparison.
3. The scientific goals of the study need to be more clearly defined. The motivation for investigating BVOC emissions specifically in this region is not sufficiently established in the Introduction. Merely determining which model version yields "more accurate" results for a specific location offers limited scientific significance. I encourage the authors to articulate the broader implications of their findings and to better structure the introduction to highlight the necessity of this research.
4. The overall presentation quality requires significant improvement. The English language needs careful polishing to ensure clarity and flow. Furthermore, the figures are currently quite simple and lack consistency in terms of size and font. This suggest the manuscript was not well prepared for top journals such as ACP.
Citation: https://doi.org/10.5194/egusphere-2025-5579-RC2
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This study investigates the differences in biogenic volatile organic compound emissions derived from MEGAN v2.1 and v3.2 over the Qinghai–Tibet Plateau and evaluates their impacts on surface ozone using WRF–CMAQ simulations for August 2022. The topic is relevant given the ecological sensitivity of the QTP and the large uncertainties in BVOC emissions in the data-scarce regions. The modeling framework is appropriate, and the analysis is organized. The authors provide a systematic comparison of simulated total BVOC, isoprene, and monoterpene emissions and demonstrate pronounced spatial differences in southeastern Tibet and the Hengduan Mountains.
Despite these strengths, the scientific novelty of the work is limited. The central finding that MEGAN v3.2 produces substantially lower isoprene emissions than v2.1 has been reported in previous studies, and the resulting reduction in ozone formation relative to v2.1 is largely expected. Similarly, the conclusion that BVOC-induced ozone enhancements are stronger in high-NOx areas such as Lhasa and Xining and negligible in NOx-scarce regions of southeastern Tibet is to be expected. This study mainly confirms known model behavior rather than providing new mechanistic insights or conceptual advances.
The observational evaluation does not strongly support the preference for either emission inventory. The indirect constraints using surface ozone measurements and satellite-derived HCHO vertical column densities and total-column ozone show only marginal differences between the two simulations. These differences are not sufficiently robust to conclusively validate one inventory over the other, particularly given the coarse sensitivity of column measurements to surface BVOC emissions and the absence of in situ BVOC observations. Furthermore, the model high biases in comparison to surface and column ozone observations far exceed the differences caused by different BVOC emissions. Additionally, the recommendation to prioritize MEGAN v3.2 is not firmly supported by observational evidence.
While the study is technically adequate and regionally relevant, its contribution is limited by a lack of novelty and weak observational constraints. Without additional insights, new data, or methodological advances, the current work does not meet the novelty threshold required for publication in a high-quality atmospheric science journal