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 NO_x 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.