Volatile organic compounds in ambient air of Delhi

Delhi is one of the most polluted cities in the world with a rapidly growing population. Huge amount of VOCs is released into the atmosphere from both anthropogenic and biogenic emissions. Various types of VOCs are released from anthropogenic sources such as disinfectants and cleansers, paints and varnishes, wood preservatives, aerosol sprays, room fresheners, dry cleaners and organic solvents. Another important anthropogenic source is burning of fossil fuels in motor vehicles, which also releases VOCs. Various plants species also release VOCs like isoprene (biogenic VOCs) which upon oxidation with atmospheric oxidants like ozone (O₃), nitrate (NO₃) and hydroxyl radicals (OH) forms less volatile products which on further reaction forms secondary organic aerosols (SOA). VOCs are also responsible for formation of tropospheric ozone which is one of the major criterion air pollutants and causes various health issues.

Around 32 samples of VOCs have been collected in the NCT of Delhi using charcoal tubes from the selected sites, VIZ., Okhla Phase 2 (OKHL, Industrial site), Sri Aurobindo Marg (SAM, traffic intervention site), Income tax office (ITO, traffic intervention site), Jawaharlal Nehru University (JNU, Institutional site). Sample preparation has been done following the protocol given by NIOSH 1501 method for xylene analysis, which is widely accepted as a “golden standard” for Industrial Hygiene sampling. Collected samples were run on GC-FID and concentration of VOCs is determined. The average concentration of Total VOCs at SAM is found to be 382.07µg/m³ while it is 200.14, 242.63 and 452.62 µg/m³ at JNU, OKHL and ITO, respectively. Out of all the VOCS, benzene and toluene represents the highest percentage with benzene representing a percentage of 17%  and 18% at SAM, JNU, Okhla and ITO, respectively and Toluene  contributing to a percentage concentration of 15% , 13%, 16% and 15% respectively at SAM , JNU, Okhla and  ITO thus owing to high vehicular emissions in Delhi. Individual average concentration at evening is higher than individual average concentration at morning at all chosen sites.  Also individual concentration of benzene and toluene is higher than other VOCs being 64.14 µg/m³ and 59.13 µg/m³ respectively at SAM, 35.64 µg/m³ and 25.83 µg/m³ at JNU, 79.6 µg/m³ and 69.9 µg/m³ at ITO and 41.92 µg/m³ and 37.80 µg/m³ at Okhla. It has planned to evaluate both the carcinogenic and non-carcinogenic risk associated with the chosen VOCs. This research will help us to get knowledge of sources of emission of VOCs. Further we will get a knowledge of the carcinogenic and non-carcinogenic impacts of VOCs and the percentage of population in Delhi which is getting directly or indirectly exposed to the carcinogenic VOCs. Hence it would help us in determining the health risk associated with VOC emission which would help in formulating effective strategies for controlling VOC emission. This would further aid us in reducing tropospheric ozone which is also a pollutant of concern. This study can also be used further in understanding atmospheric chemical reactions, photochemical smog pollution, assessment and forecast of possible change in atmospheric environment on the regional/global scale.