# Isoprene Emissions, Oxidation Chemistry and Environmental Impacts
## 7 Deforestation and Reforestation and Their Environmental Impacts
When cropland and urban regions are excluded, this means that there is space for an extra 0.9 billion hectares of canopy cover than currently exists (Figure 7), as calculated based on the European Space Agency's land cover model [177]. The paper by [PERSON] et al. [176] has been interrogated, related to calculations of the carbon storage potential of these 0.9 billion hectares of extra canopy cover (reported at 205 Gc). This carbon capture estimate represents a value 20 times that of the current annual fossil fuel emissions and a third of total historical anthropogenic carbon emissions [178]. The 205 Gc figure also seems to ignore carbon that is currently stored in these regions [179], and thus greatly overestimates the carbon storage potential of the extra canopy cover. The uncertainty over how much potential future reforestation may affect carbon sequestration continues to motivate research, but there is also great interest in whether reforestation can mitigate temperature conditions and offer a direct global cooling effect. As well as reforestation having a direct impact on the world's climate through land cover, there is also an indirect impact (e.g., oxidizing capacity of the atmosphere, increased SOA, and ozone formation) through the resulting increase in isoprene emissions. A preliminary study of climate change due to global deforestation and reforestation have been investigated by assuming 50% reduction and 100% increase of isoprene emissions in the STOCHEM-CRI model, respectively. Decreased isoprene emissions due to deforestation lead to enhanced OH levels (Figure 8a), whereas increased isoprene due to reforestation leads to more OH depletion over the tropical forested regions (Figure 8b) in the isoprene source regions. There is a tipping point in isoprene chemistry where OH recycling peaks and then starts to decrease as more isoprene is added and commensurately less OH is regenerated, which needs to be investigated further. The formation of ozone is found to be reduced in the deforestation scenario (Figure 8c) due to the decreased peroxy radicals formed from the oxidation of isoprene with OH. The ozone is also decreased in the tropical forested region for the reforestation scenario (Figure 8d) which is due to the  
Figure 7: Global distribution of 0.9 billion hectares of extra canopy cover, which could exist outside of cropland and urban regions, based on the European Space Agency’s land cover model [177]. The figure is adapted from [PERSON] et al. [176]. increased organic peroxides (ROOH) formation with increased RO\({}_{2}\) and HO\({}_{2}\). However, the increased NOx over the equatorial oceans combined with high levels of water vapor results in an increase in ozone by up to 30% (Figure 8d). The increase of OH due to deforestation can decrease CH\({}_{4}\) levels in the forested region by up to 0.2% (Figure 8e), which is very small, so deforestation does not have any overall environmental impact in terms of the decreased lifetime of CH\({}_{4}\). However, the decrease of OH due to reforestation can increase CH\({}_{4}\) levels throughout the globe by up to 1% (Figure 8f), which can have an environmental impact in terms of global warming potential (GWP). Figure 8: The percentage changes of annual surface mixing ratios of (**a**) OH, (**c**) O\({}_{3}\), (**e**) CH\({}_{4}\), simulated by STOCHEM-CRI following 50% reduced isoprene emissions, and (**b**) OH, (**d**) O\({}_{3}\), (**f**) CH\({}_{4}\) simulated by STOCHEM-CRI following 100% increased isoprene emissions. With the high uncertainty of the isoprene emission inventory, it may be asked why research into the environmental significance of isoprene is so important. Future changes in climate and land use might lead to substantial changes in the biogenic isoprene emission, which would further influence the radiative balance in the global climate as well as the air quality in urban areas. Isoprene is integral in the formation of ozone and aerosols [83], both of which pose serious health concerns and negative environmental impacts.