At least 15 key studies have looked at air pollution in Delhi over the last 18 years, the first three cited by the SC in its 1998 judgment on CNG in public transport. No one followed up the rest
1997: Deaths due to air pollution. Economist Dr Maureen Cropper, then associated with World Bank, collaborated with NDMC to find that between 1991 and 1994, deaths due to respiratory and cardiovascular reasons could be linked to air quality then prevailing.
1997-98: Air pollution and hospital visits. AIIMS found when “ambient levels of pollutants exceeded national standards on most of the days… emergency room visits for asthma, COPD and acute coronary events increased (over a two-year period) by 21.30%, 24.90% and 24.30% respectively”.
1996-98: Chronic respiratory symptoms. Dr S K Chhabra, Vallabhbhai Patel Chest Institute, found 20-25% of Delhi’s adult population with chronic respiratory symptoms, with the rate of occurrence twice that of adjoining rural areas.
2000: Pollution and health: A study done for the Harvard University Project by Centre for Occupational and Environmental Medicine at Maulana Azad Medical College and VPCI highlighted the need for more research on the effects of pollution on health.
2002: Vitamin D sinking. St Stephens Hospital study on Vitamin D levels in 9- to 24-month-old children from the “more polluted” Mori Gate area and “less polluted” Gurgaon on the outskirts found a 54% dip in those from the central Delhi hub.
2004-08: Asthma alarm. A joint study by Dr Raj Kumar, head of National Centre of Respiratory Allergy, Asthma & Immunology, and researchers from Delhi University’s geology department found asthma in 7.7% of 3,500 children aged 7 to 15.
2007: Diesel and pollution. IIT Delhi’s Centre for Atmospheric Sciences found “emissions of pollutants may exceed” limits with vehicular growth and concluded that “control” was required for “commercial diesel vehicles in Delhi”.
2008: Worse than the rest. Kolkata-based Chittaranjan National Cancer Institute, in a study commissioned by the Central Pollution Control Board on 6,000 adults, found that the rate of health problems due to air pollution was much higher than that in a control group in West Bengal.
2009: pollution map. National Capital Region Planning Board commissioned a consulting firm to map sources of pollutants in all monitoring stations; it found air pollution far exceeded permissible limits.
2012: toll on children. CNCI and CPCB found that 43% of 16,000 schoolchildren from 36 Delhi schools had “poor or restrictive” lungs.
2012: Dangerous vehicles. A study on sources of air pollutants during Commonwealth Games by the Ministry of Earth Sciences found a high contribution from vehicular pollution.
2013: Much more polluted. JNU’s Dr P K Khillare found that “residential areas of Delhi are significantly more polluted than their counterparts in other countries”.
2013: Students at risk. World Allergy Organisation Journal reported high respiratory disorder symptoms among students living in Chandni Chowk (66%) in north Delhi, Mayapuri (59%) in west Delhi and Sarojini Nagar (46%) in south Delhi.
2014: Land use. Naresh Kumar, associate professor at University of Miami, authored a study that found that after change in land use norms in Delhi, the surrounding areas of NCR — Faridabad, Gurgaon, Noida and Ghaziabad — air pollution rose significantly.
2015: Schools in trouble: A study on five schools in Delhi by Greenpeace in February found pollution levels much above acceptable limits.