Affordable Air Quality Monitoring for Improved Air Quality Management in West Africa Poor air quality damages the lives and livelihoods of millions of people and is predicted by the World Health Organisation (WHO) to become the world's largest cause of preventable death by 2030. Those living in Low- and Middle-Income Countries (LMICs) and cities are particularly affected, both through short-term acute effects and an accumulated life-long reduction in quality of life and health. There is a major opportunity to co-design and co-produce a highly fault-tolerant system for air pollution measurement, that is fully open-source, and built from easily available low cost and off-the-shelf components. The ambition is that this approach would be scale-able and could be sustained in LMICs by in-country practitioners at modest cost, long-term. New measurements can then be coupled to integrated assessment models developed by in-country agencies with our support to enhance their decision-making capacity on air pollution mitigation. This modelling will use a tool developed by project partners in the University. This new innovation for monitoring and modelling, can catalyse action and support long-term beneficial change, initially in our early adopter partner countries, and then applied to other LMICs.  Recent research from the University of York's Wolfson Atmospheric Chemistry Laboratories (WACL) has developed a low power, highly fault tolerant technology based on the clustering of multiple low-cost air pollution sensors to provide high quality measurements of target air pollutants. This approach exploits the simplicity, modest cost and high reliability of state-of-the-art sensors and electronics, but significantly improves the quality of data collected. The real-world use of sensor technologies has been slowed due to issues relating to poor individual sensor data quality. York have developed a technology that uses multiple sensors of the same type to solve the two key outstanding barriers to application in LMICs, that of sensor-to-sensor variability and unexpected sensor failure. The aim is to enable a self-supporting user community that can build and fix its own instruments and help improve on our initial designs. This approach differs fundamentally from the prevailing paradigm of a top-down commercial services model which has for many years failed to function in LMICs.  The Stockholm Environment Institute centre (SEI) in the Department of Environment and Geography at the University of York has been working with the Ministries of Environment in Togo and Cote d'Ivoire and the Ghana Environment Protection Agency, and the University of Lomé, Togo and Université Félix Houphouët-Boigny in Cote D'Ivoire to develop national models using LEAP-IBC (developed by SEI), to support national low-emission planning. We will build on this work applying LEAP-IBC to Lomé, Abidjan, Accra, and another Ghanaian city (e.g. Kumasi) where no such tool is available, and there is limited or no regular monitoring. This will allow them to develop emission inventories of key air pollutants, baseline and mitigation emission projections, and to estimate the resulting concentrations of PM2.5 and the associated human health impacts. We will work with local academics and planners to support the development of the analysis, guiding them through the data collection, model design, model validation and extraction of results. Working with the University of Colorado and WACL, we will further develop the GEOS-Chem Adjoint model inputs to LEAP-IBC that converts emissions in LEAP-IBC to concentrations of PM2.5 and ozone in these cities.  The inclusion of this modelling, developed by planners in Ghana, Cote d'Ivoire and Togo will also allow for an understanding of how the monitoring and modelling can be mutually beneficial to provide the evidence needed for the further development, implementation and monitoring of air quality plans in these cities and opportunities to achieve ambient air quality standards in cities. The Global Challenges Research Fund (GCRF) supports cutting-edge research to address challenges faced by developing countries. The fund addresses the UN sustainable development goals. It aims to maximise the impact of research and innovation to improve lives and opportunity in the developing world.