Polluted air is a scary story unfolding in India. Even after two decades of air quality regulations and management, air pollution remains the fifth-largest killer in the country. A few metro cities that had started to act are finding it increasingly difficult to hold on to the initial gains; more cities are showing up as pollution hot spots; smaller and mid-sized towns are more polluted than the metros; and more cities are falling into the pincer grip of multi-pollutant crisis with serious public health consequences. The latest available official air quality data shows 78% of cities do not meet air quality standard for tiny particles. A great part of urban population breathes air laced with particulates far beyond the standards. More than half of these cities have particulate levels that are officially classified as critical. Particles can be so tiny that even our nose and throat cannot trap and excrete them. They carry toxic chemicals and metals into our airways and lower lungs. The tinier ones from vehicle tailpipes and other combustion sources can go directly into our blood stream and invade our body. The reason why the World Health Organization (WHO) also says there is no safe level below which symptoms go away. Air has now begun to get heavy with more pollutants, adding to the deadly cocktail. Nitrogen oxide, which causes serious respiratory diseases, was not a problem even a decade ago. But now, 13 big cities have exceeded the standards for this pollutant with several of them recording critical levels. Yet, we only know what we monitor. Most cities and several critical pollutants are not part of the air quality monitoring grid yet. Because Delhi monitors, so it knows that ozone, hitherto an unknown danger, now exceeds standards frequently. Carcinogenic benzene and polycyclic aromatic hydrocarbons that are carcinogens have recorded unacceptable levels. We know from the Global Burden of Disease (GBD) report that toxic air worsens symptoms of ischaemic heart disease, stroke, chronic obstructive pulmonary disease, asthma, lung cancer and acute lower respiratory tract infection. This causes premature deaths and loss of healthy life years due to illness. India’s GBD report shows ischaemic heart disease causes half, and strokes cause 26% of the total air pollution-related premature deaths in India. The rest is dominated by respiratory conditions and cancer. Most extensive scary evidences have come from the epidemiological study on children in Delhi carried out by the Central Pollution Control Board and Chittaranjan National Cancer Institute in Kolkata, and published in 2012. This study had covered 11,628 children from 36 schools in different parts of Delhi and in different seasons. Every third child has reduced lung function. There is a marked increase in the number of biomarkers like alveolar macrophages (the first line of cellular defence against inhaled pollutants) in the sputum of children, which shows greater exposure to particulate pollution. Sputum of Delhi’s children contains four times more iron-laden macrophages than those from cleaner environs, indicating pulmonary haemorrhage. They have found the level of these biomarkers in children higher in areas with high particulate levels. How much more evidence do we want our children, elderly and the rest to generate to get our government to acknowledge the seriousness of this risk and act on it? Local evidences are only reconfirming what the world already knows from large-scale studies across global cities that have already proven not only respiratory and cardiac impacts of air pollution, but also a range of other health outcomes including diabetes, hypertension, low birth weight, cancer and effects on foetus and brain. Pollution hurts not only our health, but also our economy. The World Bank’s India— Diagnostic Assessment of Select Environmental Challenges, released in 2013, has shown that the cost of particle pollution-related health damage already amounts to 3% of India’s gross domestic product (GDP), but its mitigation will cost much less than 1% of GDP. But cost-benefit analysis is still not part of India’s fiscal planning. Rapid motorization and poor air pollution control in other sectors will only add to the health cost. The mandate is clear. Cities will have to fulfil the 12th Five-Year Plan (2012–17) target of meeting the ambient air quality standards by the end of the Plan period. This will require time-bound action plans for each source of pollution, especially vehicles that emit toxic fumes. Leapfrog emissions standards to Euro VI by 2020 and reinvent mobility in cities. Cities need to issue health advisories on a daily basis, put in place pollution emergency measures for smog episodes, and short- and medium-term measures for more lasting and durable change to meet clean air standards in a time-bound manner. We cannot fail in this. Anumita Roychowdhury is executive director (research and advocacy) at Delhi-based non-profit Centre for Science and Environment (CSE). She is also the head of CSE’s air pollution and clean transportation programme.