On September 26th, 2011, the World Health Organization (WHO) released a compilation of air quality data from 1100 cities across the world and estimated the corresponding health impacts on premature mortality and morbidity - Delhi is among the top 10 for cities with the worst air quality. The National Capital Region (NCR) of Delhi grew rapidly in the past two decades. As a rapidly expanding city, demands for transportation, energy generation, construction, waste generation, domestic cooking and heating, and industrial activity grew significantly in the last decades, contributing to air pollution across the city borders and resulting in premature mortality and respiratory impacts. In March, 2009, the Central Pollution Control Board (CPCB) of India declared Delhi as “India’s Asthma Capital”.

The city now covers an estimated area of ~900 Sq. km, including new townships and satellite centers such as Noida and Gurgaon. In 2007, population of NCR was estimated at ~16 million. This figure is expected to reach ~22.5 million in 2025 (See Interactive Urbanization Map on BBC, 2005). This page presents a summary of (and access to) articles and information on air quality in Delhi and its management. 

Air Quality Monitoring in Delhi
CPCB and the Delhi Pollution Control Committee (DPCC) operate Continuous Air Quality Monitoring Stations (CAMS) at ~10 stations and manually at some other stations. Click on the image to access air quality monitoring data from these networks (colored dots on the map represent locations where monitoring stations were operated by various organizations during the 2010 Commonwealth Games). The list below presents direct links to real time monitoring data at select locations

• Income Tax Office
  
• Central Pollution Control Board
  
• Delhi College of Engineering
  
• Siri Fort Sports Complex
  
• Punjabi Bagh
  
• Mandir Marg
  
• R. K. Puram
  
• Indira Gandhi International Airport
  
• Civil Lines
  

How bad is the air quality in Delhi?
Over the past decade, the Delhi government introduced some green initiatives to address the air pollution problem in the city. Yet, there still remains a tremendous amount of potential to reduce its impacts as the demand rises for infrastructure and services. The air quality levels have deteriorated substantially, in spite of measures like the mass conversion of public transport buses, 3 wheelers, and a fraction of private vehicles from diesel and petrol base to compressed natural gas (CNG). An analysis of the air quality monitoring data from 2006 to 2010, in the form of air quality index (AQI) is presented in the SIM-air working paper No.35

The winters are especially worse, firstly due to an increase in the pollutant emission rates originating night time heating needs and further enhanced by the meteorological conditions. This is also highlighted in the AQI analysis, where the winter months register the worst in any given year. This trend is also deteriorating, with worse stats recorded in the recent years (see Sim-air working paper. No.35).

An analysis of the role of meteorology on air pollution in Delhi is presented as a 20 year modeling study using tracer emissions and how the emissions disperse month by month from 1990 to 2009 is described is detail in SIM-air working paper No.31. The tracer simulations over the National Capital Region (NCR) of Delhi conclude that, irrespective of constant emissions over each month, the observed concentrations are 40% to 80% higher in the winter months and 10% to 60% lower in the summer months, when compared to the annual average tracer concentrations (see the 20yr animation). A version of this paper, along with excerpts from other working papers on Delhi, India, is now published in the Journal of Environmental Monitoring and Assessment, "Role of Meteorology in seasonality of air pollution in megacity, Delhi, India".

What are the sources of air pollution in Delhi?
No single sector is responsible for Delhi 's air pollution. Rather, it is a combination of factors including industries, power plants, domestic combustion of coal and biomass, and transport (direct vehicle exhaust and indirect road dust) that contribute to air pollution. Seasonal changes in demand for fuel and natural pollution result in differing sources of air pollution in summer and winter. These need to be taken into account to maximize the effectiveness of anti-pollution initiatives. The results of source apportionment of the urban air pollution in Delhi, conducted by the Georgia Tech University (USA) in 2005. A summary of the source apportionment results and a discussion on the air quality management in Delhi (then and now) is presented in the SIM-air working paper No.22.

Apart from biomass burning and ambient dust, transportation and industries are major contributors to air pollution in Delhi . With a growing city, the corresponding transportation needs are fueling a rise in private vehicles (2 and 4 wheelers) and taxis and autorickshaws. As a result, operating traffic speeds have reduced for all vehicles, thus increasing idling time and pollution. The efforts to address this by building flyovers that connect and bypass major junctions in the city have not yielded results as expected. For one, this solution addresses only the supply side of the equation and does not influence demand management. In fact, as it becomes easier to take a private vehicle, the number of vehicles have increased (about 1000 new registrations per day in 2006) thus negating many of the planned improvements. 

An analysis and discussion on the growing emissions (criteria pollutants and GHG's) from the urban passenger transport with case studies from 20 cities (big, medium, and small) in India is presented in the SIM-air working paper No.24.

What happened in Delhi, during the 2010 Commonwealth Games in Delhi?
An air quality forecasting system was developed for the NCR of Delhi, by France based Aria Technologies SA and Leosphere SA, with funding from the Government of France, and in technical collaboration with the Central Pollution Control Board (CPCB) of India. The system is the first pilot in India (edited 2 min video on the Live Mint, March, 2010) and was launched before the start of the Commonwealth Games in October 2010 (link to the press event organized by the Ambassador on France and Chairman of CPCB). The air quality forecasting system is now operational and issuing daily reports to inform on the movement of the criteria pollutants in the city. The daily reports are updated @ 6 AM with forecasts for 48 hours. More details on the program @ air quality forecasting system for Delhi.

The forecasting system is supported by the meteorological model WRF and 3D Eulerian chemical transport models CHIMERE/FARM, utilizes a geo-referenced and time-profiled emissions inventory (segregated into multiple sectors) @ 1km x 1km resolution over the NCR region. The daily updates from the system include

• Animations of hourly maps for the six criteria pollutant concentrations
  
• Animations of hourly maps for the meteorological fields
  
• Daily (24 hour) average concentrations for the six criteria pollutants
• Air Quality Index (AQI) @ 37 locations in Delhi
• Time series of pollutant concentrations @ select locations
• Vertical profiles @ select locations (available up on request)
• An interface with "google earth".

What is the role of Metro Rail in controlling air pollution in Delhi?
In 2002, a much awaited 65 km metro rail system was introduced in Delhi. The Phase II metro system is also operational for most part, expanded also to the satellite cities of Noida and Gurgaon, including an express line from the central Delhi to the international airport, with an estimated additional coverage of 130 km. The Metro has proved itself to be a popular and efficient public transport system and has already contributed towards changing peoples mode of transport from private to public. From the two phase, the estimated ridership is approximately 2 million passengers a day, which is substantial compared to the on road transport in Delhi and the congestion levels on the roads.

An analysis of the expected benefits on the metro system on local air pollution and health exposure are estimated and presented as part of the SIM-air working paper No.32. As the metro expands, with the expected growth in ridership, estimates suggest an immediate reduction of at least 10 percent in the criteria pollutants like RSPM and NO_x in 2010. While the BRT and Metro Rail is effective in improving the traffic conditions and creating opportunities to shift people from personal to public transport, an equal emphasis should be given to promote walking and cycling – both to build a sense of community and a vibrant urban space as well as to promote movement of people that results in “zero emissions”.

What is the role of 3-Wheeler Autorickshaws on air pollution in Delhi?

An overview of an experiment to measure the emissions from a variety of 3-wheelers in Delhi and assess their role on air pollution is Delhi is presented in the SIM-air working paper No.28. This paper describes the methodology (recruiting, facilities, instruments, and sampling) used in an emissions testing campaign followed by detailed characterization of particulate matter (PM) emitted by “real-world” auto-rickshaws. The measurement campaign was conducted in the National Capital Region of Delhi, India, in September 2009, by researchers from the University of British Columbia, Canada. Results from the survey and filter analysis are published in journals papers in 2010/11.