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AbstractFine particulate matter (PM_2.5) poses significant health risks, particularly to children; yet, ambient air quality studies in school environments across Kumasi, Ghana, remain limited. This study utilized low-cost Airnote sensors and meteorological data (wind speed and wind direction) from the ERA5-Land Reanalysis to assess levels of PM_2.5pollution across six senior high schools in Kumasi between 2022 and 2023, capturing spatial and seasonal variability during both the dry and wet seasons. Results revealed an annual median PM_2.5concentration of 17.18 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$, exceeding the WHO annual guideline of 5 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$. Diurnal patterns exhibited bimodal peaks aligned with morning and evening commuting and domestic activities, driven by traffic emissions, biomass burning, and informal waste burning. Pollution levels were notably elevated during weekdays and Saturdays but lower on Sundays. Median concentrations were highest at SHS E (20.91 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$), followed by SHS A (19.22 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$), SHS F (18.16 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$), and SHS D (16.71 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$), while SHS B (15.32 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$) and SHS C (12.76 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$) recorded the lowest levels. Seasonal differences were pronounced: the dry season showed significantly higher pollution (mean = 26.82 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$) than the wet season (mean = 13.18 $$\mu$$ $\mu$g/m$$^3$$ $_{}^3$), owing to reduced rainfall and limited atmospheric dispersion. Conditional Bivariate Probability Function (CBPF) analysis and HYSPLIT back-trajectory modeling identified dominant pollution sources, including nearby traffic corridors, domestic combustion activities, unmanaged waste burning, and long-range Saharan dust transport, with clear seasonal shifts in source directionality. Spatial variability in PM_2.5concentrations was further influenced by land-use characteristics and topography surrounding each school. These findings underscore the need for localized air quality management strategies, particularly in vulnerable environments like schools, to mitigate health risks and enhance urban air quality governance. Graphic Abstract 

Abstract The Regional Aerosol Model Intercomparison Project (RAMIP) is designed to quantify the forcing and climate impacts of mid-21st century anthropogenic aerosol and precursor gas (AA) emissions reductions (both industrial and biomass burning), by comparing a weak (SSP3-7.0) versus strong (SSP1-2.6) level of air quality control aerosol emissions pathway. AA emissions reductions experiments include global (GLO), East Asia (EAS), South Asia, Africa and the Middle East (AFR), and North America and Europe (NAE). Here, we use RAMIP time-slice simulations with fixed sea surface temperatures and sea-ice distributions from nine models to quantify the aerosol effective radiative forcing (ERF), including aerosol radiation (ERF_ari) and aerosol cloud interactions (ERF_aci). The multi-model global mean net ERF_ari+aciis $0.77\pm 0.25$W m⁻²for GLO, and three of the four regional perturbations yield a significant positive net ERF_ari+aci(up to $0.15\pm 0.07$W m⁻²for EAS). In all cases, net ERF_ari+aciis dominated by aerosol-cloud interactions, which are largely due to reduced cloud scattering. Of the four regions, NAE yields the largest forcing efficiency whereas AFR yields the weakest. Although the areas outside our four target regions contribute 25% to the GLO aerosol optical depth reduction, they disproportionately contribute 44% to the GLO net ERF_ari+aci. The multimodel regional mean net ERF_ari+acifor three regional perturbations is much larger (up to $1.64\pm 1.36$W m⁻²for EAS) than the corresponding global mean value. However, these regional values are even larger (up to $2.69\pm 1.72$W m⁻²for EAS) under global aerosol reductions, implying remote emission reductions represent a sizable contribution (up to $1.05\pm 0.56$W m⁻²for EAS). These large regional ERFs will in turn drive relatively large regional climate impacts, which continue to be underappreciated in most policy discussions. 

Framework for analysis of PM_2.5estimates. 

Abstract Global surface warming has accelerated since around 2010, relative to the preceding half century^1–3. This has coincided with East Asian efforts to reduce air pollution through restricted atmospheric aerosol and precursor emissions^4,5. A direct link between the two has, however, not yet been established. Here we show, using a large set of simulations from eight Earth System Models, how a time-evolving 75% reduction in East Asian sulfate emissions partially unmasks greenhouse gas-driven warming and influences the spatial pattern of surface temperature change. We find a rapidly evolving global, annual mean warming of 0.07 ± 0.05 °C, sufficient to be a main driver of the uptick in global warming rate since 2010. We also find North-Pacific warming and a top-of-atmosphere radiative imbalance that are qualitatively consistent with recent observations. East Asian aerosol cleanup is thus likely a key contributor to recent global warming acceleration and to Pacific warming trends. 

Abstract. Limited data availability and distinct regional characteristics of sources lead to a wide range of future aerosol emission projections for Africa. Here, we quantify and explore the implications of this spread for climate and health impact assessments. Using the Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants (ECLIPSE), the Shared Socioeconomic Pathways (SSPs), and the United Nations Environment Programme (UNEP) emission projections, we find high scenario diversity and regional heterogeneity in projected air pollution emissions across Africa. Baseline emissions also vary in their sectoral split. Using 10 different emission pathways as input to the Oslo chemical transport model version 3 (OsloCTM3), we find that regionally averaged annual mean population-weighted fine particulate matter (PM2.5) concentrations exhibit divergent trends depending on scenario stringency, with the eastern Africa PM2.5 concentrations increasing by up to 6 µg m−3 (37 %, SD ± 2.7 µg m−3) by 2050 under the UNEP Baseline, SSP370, and ECLIPSE current legislation scenarios. In almost all cases, excess deaths increase substantially, with increases of up to more than 2.5 times compared to the baseline. We also find a net positive aerosol-induced radiative forcing across Africa in all scenarios by 2050, except two high-sulfur emission UNEP scenarios, with values ranging from 0.03 W m−2 in SSP119 to 0.27 W m−2 in SSP585. The wide spread in projected emissions and differences in sectoral distributions across scenarios highlight the critical need for accurate activity data and harmonization efforts in preparation for upcoming assessments such as the 7th Assessment Report of the Intergovernmental Panel on Climate Change.