This advocacy guide is aimed at supporting civil society organisations (CSOs) in making the case for the political prioritisation of air pollution as a critical risk factor for noncommunicable diseases (NCDs), including mental health and neurological conditions. The guide aims to assist CSOs in their preparations for the fourth High-Level Meeting of the UN General Assembly on the prevention and control of NCDs and the promotion of mental health and well-being (HLM4), happening on 25 September 2025 in New York, and its follow-up.