Articles | Volume 26, issue 18
https://doi.org/10.5194/acp-26-13121-2026
https://doi.org/10.5194/acp-26-13121-2026
Research article
 | 
17 Sep 2026
Research article |  | 17 Sep 2026

Enhanced nocturnal N2O5-ClNO2 chemistry in Delhi under reduced NO conditions

Yijing Chen, Cheng Wu, Epameinondas Tsiligiannis, Ravi Kant Pathak, Jan B. C. Pettersson, Harsh Raj Mishra, Gazala Habib, Geetam Tiwari, Kebin He, Jingkun Jiang, and Mattias Hallquist

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Cited articles

Acharja, P., Ghude, S. D., Sinha, B., Barth, M., Govardhan, G., Kulkarni, R., Sinha, V., Kumar, R., Ali, K., Gultepe, I., Petit, J.-E., and Rajeevan, M. N.: Thermodynamical framework for effective mitigation of high aerosol loading in the Indo-Gangetic Plain during winter, Sci. Rep., 13, 13667, https://doi.org/10.1038/s41598-023-40657-w, 2023. 
Aggarwal, S., Bansal, P., Wang, Y., Jorga, S., Macgregor, G., Rohner, U., Bannan, T., Salter, M., Zieger, P., Mohr, C., and Lopez-Hilfiker, F.: Identifying key parameters that affect sensitivity of flow tube chemical ionization mass spectrometers, Atmos. Meas. Tech., 18, 4227–4247, https://doi.org/10.5194/amt-18-4227-2025, 2025. 
Ahern, A. T., Goldberger, L., Jahl, L., Thornton, J., and Sullivan, R. C.: Production of N2O5 and ClNO2 through nocturnal processing of biomass-burning aerosol, Environ. Sci. Technol., 52, 550–559, https://doi.org/10.1021/acs.est.7b04386, 2018. 
Bannan, T. J., Booth, A. M., Bacak, A., Muller, J. B. A., Leather, K. E., Le Breton, M., Jones, B., Young, D., Coe, H., Allan, J., Visser, S., Slowik, J. G., Furger, M., Prévôt, A. S. H., Lee, J., Dunmore, R. E., Hopkins, J. R., Hamilton, J. F., Lewis, A. C., Whalley, L. K., Sharp, T., Stone, D., Heard, D. E., Fleming, Z. L., Leigh, R., Shallcross, D. E., and Percival, C. J.: The first UK measurements of nitryl chloride using a chemical ionization mass spectrometer in central London in the summer of 2012, and an investigation of the role of Cl atom oxidation, J. Geophys. Res.-Atmos., 120, 5638–5657, https://doi.org/10.1002/2014jd022629, 2015. 
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This work extends current understanding of atmospheric chemistry across different NO regimes in Delhi. Field measurements during the early springtime of 2023 show enhanced nighttime production of N2O5 and ClNO2, driven by decreased NO and high particulate chloride concentrations. The inert particulate chloride can be efficiently activated to photolabile gases with the reduction of NO, and contributes to secondary pollution by enhancing atmospheric organics oxidation in Delhi.
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