Editing IPCC:AR6/WGI/Chapter-6 (section)

== 6.8 Perspectives ==

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Ice-core analyses can now inform trends for more SLCFs over the last millennium (such as light NMVOCs or CO) and more proxies are available to inform about past emissions. However, pre-industrial levels of SLCFs are still relatively poorly constrained. In addition, recent trends in abundances of the various types of aerosols and of NMVOCs suffer from the scarcity of observation networks in various parts of the world, in particular in the Southern Hemisphere. Such network development is necessary to record and understand the evolution of atmospheric composition.

Assessment of future air pollution changes at the urban level requires the use of a high-resolution models to properly account for non-linearities in chemistry, specific urban structures and local meteorology as well as temporal and spatial variations in emissions and population exposure. To assess the relevance of air pollution reduction policies, regional air-quality models are necessary and are still not implemented in many developing countries. To properly apply such models, the quality of spatialized emissions inventories is essential, but the production of accurate emissions inventories remain a challenge for lots of rapidly growing urban areas. The emissions reporting now planned in the official mandate of the Task Force on National Greenhouse Gas Inventories (TFI) can be a step in this direction if accompanied by efforts on spatial distribution of emissions. An integrated modelling framework associating global and high-resolution chemistry–transport models with shared protocols is missing to allow a systematic assessment of future changes on air quality at this scale.

In parallel, opportunities of progress may emerge from big-data acquisition. Big data and their mining can inform practices related to emissions or can document pollution levels if associated with massive deployment of low-cost sensors through citizen science. New generation satellite data will also give access to sub-kilometre-scale air pollution observations.

A systematic emissions modeling framework is needed to assess the LLGHG emissions changes associated with SLCF reductions induced by air pollution control in the SSP framework. The SLCF-mediated effects of large-scale technology deployment to allow climate change mitigation, such as hydrogen energy production, carbon capture and storage though amine filters, or changes in agricultural practices to limit GHG emissions and/or produce bioenergy are also not considered in the emissions scenarios.

Since AR5, the complexity of ESMs has increased to include many chemical and biogeochemical processes. These processes are necessary to quantify non-CO <sub>2</sub> biogeochemical feedbacks on the Earth system resulting from climate-driven changes in atmospheric chemistry and SLCF emissions from natural systems and, in turn, the impact of SLCFs on biogeochemical cycles. Enhanced understanding of the biological, chemical and physical processes based on experimental and observational work has facilitated advances in the ESMs. However, assessment of non-CO <sub>2</sub> biogeochemical feedbacks and SLCF effects on land and aquatic ecosystem productivity still remains challenging due to the multiple complex processes involved and limitations in observational constraints to evaluate the skill of ESMs in realistically simulating the processes. Advances will come from better understanding of the processes and mechanisms, in particular at the interfaces between components. The development of high-resolution ESMs will facilitate their evaluation against high- resolution observations.

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