Trends in tropospheric ozone, an important air pollutant and short-lived climate forcer (SLCF), are estimated using available surface and ozonesonde profile data for 1993-2019. Using a coherent methodology, observed trends are compared to modeled trends (1995-2015) from the Arctic Monitoring Assessment Programme SLCF 2021 assessment. Statistically significant increases in observed surface ozone at Arctic coastal sites, notably during winter, and concurrent decreasing trends in surface carbon monoxide, are generally captured by multi-model median (MMM) trends. Wintertime increases are also estimated in the free troposphere at most Arctic sites, but tend to be overestimated by the MMMs. Springtime surface ozone increases in northern coastal Alaska are not simulated while negative springtime trends in northern Scandinavia are not always reproduced. Possible reasons for observed changes and model behavior are discussed, including decreasing precursor emissions, changing ozone sinks, and variability in large-scale meteorology.

Understanding the costs and benefits of climate change mitigation and adaptation options is crucial to justify and prioritise future decarbonisation pathways to achieve net zero. Here, we quantified the co-benefits of decarbonisation for air quality and public health under scenarios that aim to limit end-of-century warming to 2ºC and 1.5ºC. We estimated the mortality burden attributable to ambient PM2.5 exposure using population attributable fractions of relative risk, incorporating projected changes in population demographics. We found that implementation of decarbonisation scenarios could produce substantial global reductions in population exposure to PM2.5 pollution and associated premature mortality, with maximum health benefits achieved in Asia around mid-century. The stringent 1.5ºC-compliant decarbonisation scenario (SSP1-1.9) could reduce the PM2.5-attributable mortality burden by 29% in 2050 relative to the middle-of-the-road scenario (SSP2-4.5), averting around 2.9M annual deaths worldwide. While all income groups were found to benefit from improved air quality through decarbonisation, the smallest health benefits are experienced by the low-income population. The disparity in PM2.5 exposure across income groups is projected to reduce by 2100, but a 30% disparity between high- and low- income groups persists even in the strongest mitigation scenario. Further, without additional and targeted air quality measures, low- and lower-middle-income populations (predominantly in Africa and Asia) will continue to experience PM2.5 exposures that are over three times the World Health Organization (WHO) Air Quality Guideline.

The strategies that policymakers take to mitigate climate change will have considerable implications for human exposure to air quality, with air quality co-benefits anticipated from climate change mitigation. Few studies try to model these co-benefits at a regional scale and even fewer consider health inequalities in their analyses.   We analyse the health impacts across Western and Central Europe from exposure to fine particulate matter (PM2.5) and surface level ozone (O3) in 2014 and in 2050 using three scenarios with different levels of climate change mitigation, using a high-resolution atmospheric chemistry model to simulate future air quality. We use recent health functions to estimate mortality related to the aforementioned pollutants. We also analyse the relationship between air quality mortality rate per 100,000 people and Human Development Index to establish if reductions in air quality mortality are achieved equitably.   We find that air quality-related mortality (PM2.5 + O3 mortality) will only reduce in the future following a high-mitigation scenario (54%). It could increase by 7.5\% following a medium-mitigation scenario and by 8.3% following a weak mitigation scenario. The differences are driven by larger reductions in PM2.5-related mortality and a small reduction in O3-related mortality following the sustainable scenario, whereas for the other scenarios, smaller improvements in PM2.5-related mortality are masked by worsening O$_3$-related mortality.   We find that less developed regions of European countries have higher mortality rates from PM2.5 and O3 exposure in the present day, but that this inequity is reduced following greater climate change mitigation.