Air pollution is a major global health issue, contributing to an estimated 5.2 million deaths annually. This review highlights the challenges in estimating population exposure to air pollution and its health impacts, particularly in low- and middle-income countries (LMICs) and vulnerable populations. The World Health Organization (WHO) has updated the Global Air Quality Guidelines (AQGs) based on recent evidence, but studies from LMICs remain insufficient. The evidence shows a linear relationship between PM2.5 concentrations and health risks, though recent studies suggest a supralinear relationship even at low concentrations. Globally, non-communicable diseases (NCDs) are the leading cause of death and disability, with nearly 41 million deaths annually, mostly in LMICs. Ambient air pollution is the leading environmental risk factor for NCDs, affecting nearly 99% of the global population. Vulnerable populations, including the elderly, children, and pregnant women, are at higher risk. Air pollution sources include traffic, industry, and biomass burning, with limited personal mitigation options. Monitoring and assessing exposure is challenging due to uneven coverage and data gaps. Emerging technologies and models improve exposure estimates, but more research is needed to understand the health impacts of air pollution, especially at low concentrations. Effective risk communication and evidence-based policies are crucial for reducing health risks. The review emphasizes the need for region-specific research, improved monitoring, and targeted interventions to address air pollution's health impacts. The challenges in implementing air quality policies are significant, particularly in LMICs, where the burden of disease is severe. The review calls for urgent action to reduce air pollution and improve public health.Air pollution is a major global health issue, contributing to an estimated 5.2 million deaths annually. This review highlights the challenges in estimating population exposure to air pollution and its health impacts, particularly in low- and middle-income countries (LMICs) and vulnerable populations. The World Health Organization (WHO) has updated the Global Air Quality Guidelines (AQGs) based on recent evidence, but studies from LMICs remain insufficient. The evidence shows a linear relationship between PM2.5 concentrations and health risks, though recent studies suggest a supralinear relationship even at low concentrations. Globally, non-communicable diseases (NCDs) are the leading cause of death and disability, with nearly 41 million deaths annually, mostly in LMICs. Ambient air pollution is the leading environmental risk factor for NCDs, affecting nearly 99% of the global population. Vulnerable populations, including the elderly, children, and pregnant women, are at higher risk. Air pollution sources include traffic, industry, and biomass burning, with limited personal mitigation options. Monitoring and assessing exposure is challenging due to uneven coverage and data gaps. Emerging technologies and models improve exposure estimates, but more research is needed to understand the health impacts of air pollution, especially at low concentrations. Effective risk communication and evidence-based policies are crucial for reducing health risks. The review emphasizes the need for region-specific research, improved monitoring, and targeted interventions to address air pollution's health impacts. The challenges in implementing air quality policies are significant, particularly in LMICs, where the burden of disease is severe. The review calls for urgent action to reduce air pollution and improve public health.