While the Supreme Court is attempting to ascertain the “immediate impact of fireworks and firecrackers during Diwali” by ordering a ban on their sale in the National Capital Region (NCR), at least four major government studies over the past decade have reached varying conclusions on what makes Delhi’s air so foul.
Four years before the first of these studies, the union Ministry of Environment and Forests had, in 2003, published a white paper that reported that in the three decades between 1970-71 and 2000-01, the contribution of vehicles to particulate matter in Delhi’s air had more than trebled to 72% from 23%.
The source apportionment studies carried out since then have differed on the relative contribution of sources of particulate matter in Delhi’s air. While vehicular pollution and road dust have emerged as major contributors, assessments of the role played by vehicles have varied the most widely.
Feb 2007, IIT-Delhi
A Detailed Study to Ascertain the Effect of Diesel Operated Trucks, Tempos, Three-Wheelers and Other Commercial Vehicles on the Ambient Air Quality of Delhi, sponsored by the Department of Environment, Government of the NCT of Delhi; Principal Investigator: Prof Pramila Goyal, Centre for Atmospheric Sciences, IIT-Delhi.
Three years before the 2010 Commonwealth Games, the Delhi government was concerned about the massive increase in the number of vehicles plying in the city. The study noted, “Vehicles… in Delhi increased phenomenally from 2.3 million in 1975 (MOEF, 1997) to 4.2 million in 2004, [and] has been estimated [to go up to] 7.2 million in 2016 on the basis of transport data obtained from Transport Department, 2004.”
The study was commissioned to specifically understand the contributions of vehicle of different types to vehicular air pollution. Officials said at the time that measures to mitigate air pollution generated by vehicles were not yielding results quickly enough.
The study concluded that “control on emissions of pollutants from vehicular traffic necessitates the control on the new registration of commercial diesel vehicles in Delhi”. It noted that the “emission of air pollutants [is] directly proportional to the number of vehicles and concentration of ambient air pollutants is also directly proportional to the emission of air polluting sources”. A key finding was that “tempos contribute maximum amount of concentration of NOx and PM (58%) followed by trucks (24.1%), buses (12%), cars/taxis (9.7%), small trucks (3.7%) and tractor, trailer (0.18%).” It suggested that “control may require[d]… on the new registration of diesel tempos and trucks”.
Dec 2008, NEERI, Nagpur
Air Quality Monitoring, Emission Inventory & Source Apportionment Studies for Delhi; Central Pollution Control Board (CPCB) with National Environmental Engineering Research Institute (NEERI).
The study was commissioned after the need for “better understanding” of air pollution sources was “recognised” in the Auto-Fuel Policy Document, 2002. “With this in view, oil companies in India, in association with premier research institutions, joined together with the stewardship of CPCB and MOEF to initiate a detailed study for source apportionment of ambient air pollutants,” the study said. The study was carried out in collaboration with oil marketing companies led by Indian Oil Corporation Ltd (IOCL), and the Automotive Research Association of India (ARAI), Pune, “for development of emission factors for vehicles”.
The study identified road dust as the biggest contributor (52.5%) to particulate matter in Delhi’s air, followed by industries (22.1%). It attributed only 6.6% of particulate emissions to vehicles.
For NOx, the study found industries contributed 79% and vehicles 18%; vehicles were the main source of CO and hydrocarbons: 59% and 50% respectively. It added, “Maximum vehicular pollution and road dust generation is estimated in the nearby area of India Gate.”
Emissions Inventory of Anthropogenic PM 2.5 and PM 10 in Delhi during Commonwealth Games 2010; Saroj Kumar Sahu, Gufran Beig, Neha S Parkhi for System of Air quality Forecasting and Research (SAFAR) project. Published in Atmospheric Environment, 2011.
SAFAR was developed for air quality forecasting during the Commonwealth Games, and “high resolution Emission Inventory (EI) of PM10 and PM2.5” was developed for Delhi. The inventory involved detailed activity data for the region “using Geographical Information System (GIS) technique”. SAFAR, which introduced the Air Quality Index (AQI) as a new public information tool to measure pollution, was developed by the Indian institute of Tropical Meteorology (IITM), Pune, with weather information and forecasting by the India Meteorological Department.
The study reached the “surprising” conclusion that road dust from paved and unpaved roads contributed the largest share to air pollution (55%), followed by residential sources (15%), transport and vehicular pollution (13%), industrial sources (12%), and power (5%). “Emission from the unattended source like windblown dust from paved and unpaved roads is found to be the major contributor in PM10 and PM2.5 emissions in Delhi and inclusion of this sector helped in better forecasting skill,” the study said. “Particulate pollution”, it said, “is a major problem for Delhi specially during winter and fire event festival”, and that the situation with regard to gaseous pollution (such as NOx and sulphur oxides) was “reasonably better”.
Jan 2016, IIT-Kanpur
Comprehensive Study on Air Pollution and Green House Gases (GHGs) in Delhi (Final Report: Air Pollution Component); Prof Mukesh Sharma and Prof Onkar Dikshit, Department of Civil Engineering, IIT-Kanpur; submitted to the Department of Environment, Government of the NCT of Delhi, and Delhi Pollution Control Committee.
The study carried out sampling during the winter of 2013-14 and the summer of 2014. It had five components: air quality measurements, emission inventory, air quality modelling, control options and an action plan. This study forms the basis of legislation being planned by the Delhi government, and of the Graded Action Response Plan (GRAP) framed by the Environment Pollution (Prevention & Control) Authority (EPCA) for the NCR. The EPCA was set up by the central government in 1998 following a directive of the Supreme Court.
Unlike the 2008 and 2011 studies, this study, while underlining the role of road dust, also stressed on vehicular emissions — moving vehicles, in fact, contributed to over half of Delhi’s air pollution, it said. For PM2.5, the source apportionment, according to the study, was: road dust (38%), vehicular pollution (20%), domestic sources (12%), industrial sources (11%), concrete batching (6%), hotels and restaurants (3%), municipal solid waste burning (3%), diesel gensets (2%), industrial area sources (2%), and cremation, aircraft and medical incinerators (1% each).
For NOx emissions, industrial point sources (52%) and vehicles (36%) were the biggest contributors, followed by diesel gensets (6%), the study found.