Brief on the full inclusion of PM2.5 in the 2027 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Short-lived Climate Forcers

Short-Lived Climate Forcers (SLCFs) affect the climate and are, in most cases, air pollutants. Many countries are already producing national and regional inventories of air pollutants which often include SLCFs (IPCC, 2024). Given the significance of SLCF emissions on climate and the availability of robust science and techniques to estimate emissions of SLCFs, the IPCC will develop a Methodology Report on SLCFs (IPCC/XLIX-7). 

The inclusion of PM2.5 as a directly targeted SLCF species has been discussed, however “no consensus was reached” (see Annex 1). The proposed covered species are NOx, carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs), sulphur dioxide (SO2), ammonia (NH3), black carbon and organic carbon (BC and OC; both components of PM2.5), and hydrogen (H2). 

Working Group I of the IPCC Sixth Assessment Report noted that non-carbonaceous components of primary particulate matter have both direct and indirect effects on the climate system. For example, mineral dust, can have a positive or negative climate forcing impact as well as impacts on the cryosphere, aerosol-cloud interactions and ecosystems (Annex 2). If all primary sources of PM2.5 are not addressed in the SLCF guidance, important non-carbonaceous sources of climate impacting PM such as construction dust and vehicle break and tyre wear would not be included resulting in incomplete and inconsistent inventories.