Historical and Future Changes in Air Pollutants from CMIP6 Models

• Published in: Atmospheric chemistry and physics 2020-11, Vol.20 (23), p.14547-14579
• Main Authors: Turnock, Steven T, Allen, Robert J, Bauer, Susanne E, Andrews, Martin, Deushi, Makoto, Emmons, Louisa, Good, Peter, Horowitz, Larry, John, Jasmin G, Michou, Martine, Nabat, Pierre, Naik, Vaishali, Neubauer, David, O’Connor, Fiona M, Olivie, Dirk, Oshima, Naga, Schulz, Michael, Sellar, Alistair, Shim, Sungbo, Takemura, Toshihiko, Tilmes, Simone, Tsigaridis, Konstantinos, Wu, Tongwen, Zhang, Jie
• Format: Article
• Language: English
• Subjects: Aerosols; Air; Air pollution; Air pollution control; Air pollution measurements; Air quality; Air quality measurements; Air quality models; Annual; Anthropogenic factors; Atmospheric chemistry; Atmospheric models; Biogenic emissions; Climate change; Climate change mitigation; Climate effects; Climate models; Diameters; Earth; Economic development; Economics; Emission; Emissions; Experiments; Global temperature changes; Human influences; Intercomparison; Meteorology And Climatology; Mitigation; Northern Hemisphere; Ocean, Atmosphere; Ozone; Particulate emissions; Particulate matter; Pollutants; Pollution control; Precursors; Regions; Sciences of the Universe; Simulation; Socioeconomic aspects; Suspended particulate matter; Trends
• ISSN: 1680-7316; 1680-7324; 1680-7324
• DOI: 10.5194/acp-20-14547-2020

Poor air quality is currently responsible for large impacts on human health across the world. In addition, the air pollutants ozone (O3) and particulate matter less than 2.5 µm in diameter (PM2.5) are also radiatively active in the atmosphere and can influence Earth's climate. It is important to understand the effect of air quality and climate mitigation measures over the historical period and in different future scenarios to ascertain any impacts from air pollutants on both climate and human health. The Coupled Model Intercomparison Project Phase 6 (CMIP6) presents an opportunity to analyse the change in air pollutants simulated by the current generation of climate and Earth system models that include a representation of chemistry and aerosols (particulate matter). The shared socio-economic pathways (SSPs) used within CMIP6 encompass a wide range of trajectories in precursor emissions and climate change, allowing for an improved analysis of future changes to air pollutants. Firstly, we conduct an evaluation of the available CMIP6 models against surface observations of O3 and PM2.5. CMIP6 models consistently overestimate observed surface O3 concentrations across most regions and in most seasons by up to 16 ppb, with a large diversity in simulated values over Northern Hemisphere continental regions. Conversely, observed surface PM2.5 concentrations are consistently underestimated in CMIP6 models by up to 10 µg m−3, particularly for the Northern Hemisphere winter months, with the largest model diversity near natural emission source regions. The biases in CMIP6 models when compared to observations of O3 and PM2.5 are similar to those found in previous studies. Over the historical period (1850–2014) large increases in both surface O3 and PM2.5 are simulated by the CMIP6 models across all regions, particularly over the mid to late 20th century, when anthropogenic emissions increase markedly. Large regional historical changes are simulated for both pollutants across East and South Asia with an annual mean increase of up to 40 ppb for O3 and 12 µg m−3 for PM2.5. In future scenarios containing strong air quality and climate mitigation measures (ssp126), annual mean concentrations of air pollutants are substantially reduced across all regions by up to 15 ppb for O3 and 12 µg m−3 for PM2.5. However, for scenarios that encompass weak action on mitigating climate and reducing air pollutant emissions (ssp370), annual mean increases in both surface O3 (up 10 ppb) and PM