Regional to global distributions, trends, and drivers of biogenic volatile organic compound emission from 2001 to 2020.

Biogenic volatile organic compounds (BVOCs) are important precursors to ozone and secondary organic aerosols in the atmosphere, affecting air quality, clouds and climate. However, the trend of BVOC emissions and driving factors for the emission changes in different geographic regions over the past two decades has remained unclear. Here, regional to global changes in BVOC emissions during 2001–2020 are simulated using the latest Model of Emission of Gases and Aerosols from Nature (MEGANv3.2) with the input of time-varying satellite-retrieved vegetation and reanalysis meteorology data. Comparison of model simulations with the site observations shows that the model can reasonably reproduce the magnitude of isoprene and monoterpene emission fluxes. The spatial distribution of the modeled isoprene emissions is generally comparable to the satellite retrievals. The estimated annual average global BVOC emissions are 835.4 Tg yr^-1 with the emissions from isoprene, monoterpenes, sesquiterpenes, and other BVOC comprised of 347.7, 184.8, 23.3, and 279.6 Tg yr^-1, respectively. We find that the decrease in global isoprene emissions (-0.07 % yr^-1) caused by increase in CO2 concentrations (-0.20 % yr^-1) is stronger than that caused by changes in vegetation (-0.03 % yr^-1) and meteorological factors (0.15 % yr^-1). However, regional disparities are large. Isoprene emissions increase significantly in Europe, East Asia, and South Asia (0.37-0.66 % yr^-1). The increasing trend is contributed by half from increased leaf area index (LAI) (maximum over 0.02 m² m^-2 yr^-1) and tree cover. Changes in meteorological factors contribute to another half, with elevated temperature dominating in Europe and increased soil moisture dominating in East and South Asia. In contrast, in South America and Southeast Asia, shifts in vegetation type associated with the BVOC emission capacity, which partly results from the deforestation and agricultural expansion, decrease the BVOC emission and offset nearly half of the emission increase caused by changes in meteorological factors. Overall, isoprene emission increases by 0.35 % yr^-1 and 0.25 % yr^-1 in South America and Southeast Asia, respectively. In Central Africa, a decrease in temperature dominates the negative emission trend (-0.74 % yr^-1). Global monoterpene emissions show a significantly increasing trend (0.34 % yr^-1, 0.6 Tg yr^-1) compared to that of isoprene (-0.07 % yr^-1, -0.2 Tg yr^-1), especially in strong greening hotspots. This is mainly because the monoterpene emissions are more sensitive to changes in LAI and are not subject to the inhibition effect of CO2. The findings highlight the important roles of vegetation cover and biomass, temperature, and soil moisture in modulating the temporal variations of global BVOC emissions in past two decades. [ABSTRACT FROM AUTHOR]