1. 1. WHO. Air quality guidelines -Air Pollution, global update. 2018. https://www.who.int/airpollution/data/cities/en/
2. 2. Kumar R. Effect of air pollution on respiratory system of auto rickshaw Drivers in Delhi. Ind J Occ and Env Med. 1999; 3: 171-173.
3. 3. Kumar R. A study of respiratory symptoms and lung function of welders in Delhi. Ind J Occ and Env Medicine 2000; 4: 168 - 171.
4. 4. Gaur SN, Kumar R, Sinha R. Prevalence of bronchial asthma in petrol pump workers of Delhi. Indian J Occupat Environ Med. 2003; 7: 13-16.
5. 5. Kumar R. Air Pollution and Respiratory Diseases. NCCP Text Book of Respiratory Medicine (Page No. 752-755). Editor: D Behra, Published by Jaypee Brothers P. Ltd. 2011.