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Simultaneous Observations of Nitrogen Dioxide, Formaldehyde and Ozone in the Indo-Gangetic Plain

Category: Urban Air Quality

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DOI: 10.4209/aaqr.2018.12.0484

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Mriganka Sekhar Biswas1,2, Sachin Ghude1, Dinesh Gurnale1, Thara Prabhakaran1, Anoop S. Mahajan 1

  • 1 Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Pune 411008, India
  • 2 Savitribai Phule Pune University, Pune 411007, India


  • Simultaneous observations of NO2, HCHO and O3 in the Indo-Gangetic plain (IGP).
  • Power plants located ~110 km towards the south affect the local NO2 concentrations.
  • HCHO concentrations are homogenous over the region.
  • Ozone concentrations are affected more by local sources than long range transport.


This study reports concentrations of nitrogen dioxide (NO2) and formaldehyde (HCHO) retrieved using the Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique and collocated observations of surface ozone (O3) conducted over the Indo-Gangetic Plain (IGP). Observations were conducted during the 2014 monsoon period as a part of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX). The average daytime NO2 mixing ratio was 0.81 ± 0.20 ppbv (parts per billion by volume) (range: 0.08 ppbv to 6.06 ppbv). NO2 was observed to decrease through the morning between 0600 to 0900 hours local time and then stabilise for the rest of the day. The average daytime HCHO mixing ratio was 1.93 ± 0.60 ppbv (range: 0.32 ppbv to 8.81 ppbv). Unlike NO2, HCHO increased during the early morning driven by daytime photochemical formation from hydrocarbon precursors. The averaged O3 mixing ratio during the daytime was 30.0 ± 13.0 ppbv (range: 2.7 ppbv to 81.9 ppbv) and 22.5 ± 10.2 ppbv (range: 1 ppbv to 63 ppbv) during the night time. Analyses using back trajectories found that the NO2 mixing ratios during CAIPEEX-2014 were affected by long-range transport from thermal power plants situated about 110 km to the South. The HCHO mixing ratios and O3 production did not show any indication of long-range transport but were instead dominated by local emissions. These observations suggest that in the rural IGP ozone concentrations are affected more by local sources than long range transport.


Nitrogen dioxide Formaldehyde Ozone Indo-Gangetic Plain

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