Land use change influence on atmospheric organic gases, aerosols, and radiative effects

Abstract. Biogenic volatile organic compounds (BVOC) are emitted in large quantities from the terrestrial biosphere and play a significant role in atmospheric gaseous and aerosol composition. Such emissions account for 90 % of the total global volatile organic compound (VOC) emissions and exert a significant influence on the atmosphere’s oxidation capacity. BVOCs are precursors of secondary organic aerosols (SOA), which affect the radiation budget both directly through scattering and absorption of sunlight and indirectly through modifying cloud formation, properties and distribution. Human activities have extensively altered natural vegetation cover, primarily by converting forests into agricultural land. In this work, a global atmospheric chemistry-climate model with interactive vegetation was employed to study the impacts of perturbing the biosphere through human land use change, consequently exploring changes in BVOC emissions and atmospheric aerosol burden. Given that our vegetation model simulates potential natural vegetation (PNV), a land use scheme was implemented to constrain the Tree Plant Functional Type (PFT) cover based on land transformation fraction maps from the year 2015. Two scenarios are evaluated: (1) comparing present-day land cover, which includes areas deforested for crops and grazing land, with the natural vegetation cover (PNV), and (2) an extreme reforestation scenario where present-day crop and grazing land are restored to natural vegetation. We find that, compared to the PNV scenario, present-day deforestation results in a 26 % reduction in BVOC emissions, which decreases the global biogenic SOA (bSOA) burden by 0.16 Tg (a decrease of 29 %), while the total organic aerosol (OA) burden decreases by 0.17 Tg (a reduction of 9 %). On the other hand, the extreme reforestation scenario, compared to present-day land cover, suggests an increase in BVOC emissions by 22 %, which increases the bSOA by 0.11 Tg and total OA burden by 0.12 Tg, an increase of 26 % and 6 %, respectively. The assessment includes changes in the cloud condensation nuclei (CCN) and cloud droplet number concentration (CDNC) in each scenario. In the present-day deforestation scenario, we estimate a positive total radiative effect (aerosol + cloud) of 60.4 mW m⁻² (warming) compared with the natural vegetation scenario, while in the extreme reforestation scenario, we report a negative effect (cooling) of 38.2 mW m⁻² compared to the PNV scenario.