Environmental Monitoring and Assessment

, Volume 115, Issue 1, pp 405-417

First online:

Assessment of Air Quality After the Implementation of Compressed Natural Gas (CNG) as Fuel in Public Transport in Delhi, India

  • Khaiwal RavindraAffiliated withMicro and Trace Analysis Center, Department of Chemistry, University of Antwerp Email author 
  • , Eric WautersAffiliated withFlemish Environment Agency (VMM)
  • , Sushil K. TyagiAffiliated withCentral Pollution Control Board
  • , Suman MorAffiliated withCentre for Energy Studies, Indian Institute of Technology Delhi
  • , René Van GriekenAffiliated withMicro and Trace Analysis Center, Department of Chemistry, University of Antwerp

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Public transport in Delhi was amended by the Supreme Court of India to use Compressed Natural Gas (CNG) instead of diesel or petrol. After the implementation of CNG since April 2001, Delhi has the highest fraction of CNG-run public vehicles in the world and most of them were introduced within 20 months. In the present study, the concentrations of various criteria air pollutants (SPM, PM10, CO, SO2 and NOx) and organic pollutants such as benzene, toluene, xylene (BTX) and polycyclic aromatic hydrocarbons (PAHs) were assessed before and after the implementation of CNG. A decreasing trend was found for PAHs, SO2 and CO concentrations, while the NOx level was increased in comparison to those before the implementation of CNG. Further, SPM, PM10, and BTX concentrations showed no significant change after the implementation of CNG. However, the BTX concentration demonstrated a clear relation with the benzene content of gasoline. In addition to the impact of the introduction of CNG the daily variation in PAHs levels was also studied and the PAHs concentrations were observed to be relatively high between 10 pm to 6 am, which gives a proof of a relation with the limited day entry and movement of heavy vehicles in Delhi.


CNG public transport CO NOx SO2 PM10 BTX PAHs principal component analysis