Editing IPCC:AR6/WGIII/Chapter-2 (section)

==== 2.2.2.2 Other Short-lived Climate Forcers (SLCFs) ====

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There are other emissions with shorter atmospheric lifetimes that contribute to climate changes. Some of them (aerosols, sulphur emissions or organic carbon) reduce forcing, while others – such as black carbon, carbon monoxide or non-methane volatile organic compounds (NMVOC) – contribute to warming (Figure 2.4) as assessed in WGI (Forster et al. 2021c; [[#Szopa--2021a|Szopa et al. 2021a]] ). Many of these other SLCFs are co-emitted during combustion processes in power plants, cars, trucks, airplanes, but also during wildfires and household activities such as traditional cooking with open biomass burning. As these co-emissions have implications for net warming, they are also considered in long-term emission reduction scenarios as covered in the literature ( [[#Harmsen--2020|Harmsen et al. 2020]] ; [[#Rauner--2020b|Rauner et al. 2020b]] ; [[#Smith--2020|Smith et al. 2020]] ; [[#Vandyck--2020|Vandyck et al. 2020]] ) as well as [[IPCC:Wg3:Chapter:Chapter-3|Chapter 3]] of this report. These air pollutants are also detrimental to human health (e.g., [[#Lelieveld--2015|Lelieveld et al. 2015]] , 2018; [[#Vohra--2021|Vohra et al. 2021]] ). For example, [[#Lelieveld--2015|Lelieveld et al. (2015)]] estimate a total of 3.3 (1.6–4.8) million premature deaths in 2010 from outdoor air pollution. Reducing air pollutants in the context of climate policies therefore leads to substantial co-benefits of mitigation efforts (Von Stechow et al. 2015; [[#Rao--2017|Rao et al. 2017]] ; [[#Lelieveld--2019|Lelieveld et al. 2019]] ; [[#Rauner--2020a|Rauner et al. 2020a]] ). Here we briefly outline the major trends in emissions of SLCFs.

Conventional air pollutants that are subject to significant emission controls in many countries include sulphur dioxide (SO 2 ), nitrogen oxides (NO x ), black carbon (BC) and carbon monoxide (CO). From 2015 to 2019, global SO 2 and NOx emissions declined, mainly due to reductions in energy systems (Figure 2.8). Reductions in BC and CO emissions appear to have occurred over the same period, but trends are less certain due to the large contribution of emissions from poorly quantified traditional biofuel use. Emissions of CH 4 , OC and NMVOC have remained relatively stable in the past five years. OC and NMVOC may have plateaued, although there is additional uncertainty due to sources of NMVOCs that may be missing in current inventories ( [[#McDonald--2018|McDonald et al. 2018]] ).

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'''Figure 2.8''' '''|''' '''Air pollution emissionsby major sectors from CEDS (1970–2019) and EDGAR (1970–2015) inventories.''' Source: Crippa et al. (2019a, 2018); [[#O’Rourke--2020|O’Rourke et al. (2020)]] ; [[#McDuffie--2020|McDuffie et al. (2020)]] .

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