This white paper proposes a collaborative global framework to expand geostationary (GEO) atmospheric composition monitoring to populated, undermonitored areas facing severe environmental threats. Currently, significant observational gaps exist across Africa, parts of Latin America and the Caribbean, the Pacific Islands, most of Asia (excluding Japan and South Korea), and Oceania (including Australia and New Zealand). Expanding coverage to these regions is critical due to rapid population growth and urbanization. Future megacities will concentrate populations, intensify environmental pressures, and alter land use. While high-income countries benefit from extensive ground monitoring, this resource is severely lacking in low- and middle-income nations. Without robust monitoring systems, epidemiologists cannot track health impacts, and policymakers lack the real-world observations required to evaluate pollution exposure and develop effective mitigation strategies. To complement the proposed satellite expansion, this paper also highlights the need to strengthen existing ground-based networks. By identifying coverage gaps, assessing data quality, promoting capacity building, standardizing methodologies, and enforcing quality control, the global community can enable harmonized data utilization for model validation and provide reliable datasets to inform data-based policies in developing countries. This harmonized data will also benefit global air quality models improving the skill of forecast models in developed countries. GEO satellite data is uniquely suited to fill these monitoring gaps. While Low Earth Orbit (LEO) satellites provide daily global data and ground stations capture high-frequency local conditions, GEO sensors offer a synoptic view of the daytime diurnal cycle. Their hourly measurements capture the rapid atmospheric composition changes driven by shifting emissions, transport, and chemical reactions, comprehensively covering areas between and without ground stations. This proposed expansion builds upon a highly successful foundation of existing satellite observations, which already form the cornerstone for monitoring air pollution, characterizing emission trends, and improving atmospheric chemistry forecasting. Today, data assimilation successfully combines satellite and ground-based observations with model predictions to produce corrected analyses that feed critical environmental information services. Presently, the ‘GeoAQ Constellation’ operates three UV-visible-near infrared spectrometers (GEMS on GEO-Kompsat-2B, TEMPO on Intelsat 40e, and Copernicus Sentinel-4 on MTG-S1) to observe ozone (O3), nitrogen dioxide (NO2), formaldehyde (HCHO), and sulfur dioxide (SO2) (CEOS, 2011, 2019). This white paper proposes to expand the GeoAQ Constellation by strategically adding four geostationary satellites over Africa, South America, the Middle East and India, and Oceania.