| 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.
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