Fine particulate matter, PM2.5, has been associated with significant health effects including cardiovascular diseases, lung diseases, cancer and premature deaths. The PM2.5-related health impacts are notable for megacities across the globe, but Asian megacities have been suffering much more. The Phenomenon of smog-hit cities became so common recently that the term 'airpocalypse' has become synonymous with polluted air. This study reports PM2.5-related long-term mortality for the year 2016 in 13 megacities of China, India, Bangladesh and Pakistan using an integrated exposure risk (IER) model. This study assesses the mortality associated with health outcomes attributable to PM2.5 particularly: cerebrovascular disease (stroke, CEV), ischemic heart disease (IHD), chronic obstructive pulmonary disease (COPD) and lung cancer (LC) among adults (>= 25years) and the acute lower respiratory infection (ALRI) for infants (<5years). It further provides an estimation of the potential health benefits in future years under various scenarios realizing the PM2.5 concentration levels of (a) the goals of Air Pollution Prevention and Control Action Plan target (APPCAP) for China; (b) current policies (CP) and best practice emission control (BPEC) scenarios and (c) Interim Targets (ITs) and Air Quality Guidelines (AQG) for PM2.5 for all megacities. It is estimated that in 2016, PM2.5-related mortality in Shanghai, Beijing, Chongqing, Tianjin, Guangzhou and Shenzhen was 17.6, 18.2, 10.4, 9.8, 7.6 and 6.4 thousand respectively. In Indian megacities, the premature deaths were 14.8, 10.5, 7.3, 4.8 and 4.8 thousand in Delhi, Mumbai, Kolkata, Bangalore and Chennai respectively. Total mortality in Dhaka and Karachi was estimated to be 9.1 and 7.7 thousand. The CP is not enough to protect the public health in future in all the megacities. In China, PM2.5 levels will reduce under CP but PM2.5-related deaths will increase by 14-30%, primarily due to increase in overall population growth and urban migration patterns. In other megacities, the PM2.5-related deaths will increase by 39.32-85% in CP scenario, mostly due to the increase of PM2.5 in CP scenario. Though China has taken initial steps with pollution control targets and strategy, there is an urgent need for government policy in India, Bangladesh and Pakistan. This study highlights the need for urgency in setting up decisive air quality targets by megacity authorities and advocates for joint regional efforts to control air pollution. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.