Changes in global atmospheric oxidant chemistry from land cover conversion

The natural landscape has undergone profound transformations due to human activities, with vast areas being converted for agriculture and grazing. This shift  has far-reaching consequences for the Earth's system, impacting various components such as surface reflectivity, roughness, evapotranspiration, and atmospheric composition.

To better understand the effects of land cover change on atmospheric chemistry, this study employs the chemistry–climate model EMAC to simulate two distinct scenarios. The first scenario represents the current state of land cover, characterized by widespread deforestation for agricultural and grazing purposes, with the potential natural vegetation (PNV) cover simulated by the model. In contrast, the second scenario depicts an extreme reforestation scenario, where grazing land is restored to its natural state.

The results of this study reveal that the expansion of agricultural land leads to a decline in global emissions of biogenic volatile organic compounds (BVOCs). This decrease in BVOC emissions, in turn, results in higher surface concentrations of hydroxyl radicals (OH, +5.7%) and lower mixing ratios of carbon monoxide (CO, -6.2%). Notably, this trend persists despite increased CO emissions from agricultural biomass burning.

At the same tim, the mixing ratios of nitrogen oxides (NOx) exhibit an increase (+7.8%) due to enhanced anthropogenic and natural soil sources. While regional ozone responses may vary, the global ozone production sensitivity shifts from a NOx- to a VOC-sensitive regime.

These changes have significant implications for radiative forcing, with reductions in tropospheric ozone and methane lifetimes contributing to a combined radiative effect of −60 mW m−2 (cooling). This cooling effect partially offsets the warming resulting from reduced BVOC-driven aerosol formation.