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Planetary boundary layer height modulates aerosol - water vapour interactions during winter in the megacity of Delhi
  • +19
  • Subha S Raj,
  • Ovid Krüger,
  • Amit Sharma,
  • Upasana Panda,
  • Christopher Pöhlker,
  • David Walter,
  • Jan-David Förster,
  • Rishi Pal Singh,
  • Swetha S,
  • Thomas Klimach,
  • Eoghan Darbyshire,
  • Scot T. Martin,
  • Gordon McFiggans,
  • Hugh Coe,
  • James D Allan,
  • Ravikrishna R,
  • Vijay Kumar Soni,
  • Hang Su,
  • Meinrat O. Andreae,
  • Ulrich Pöschl,
  • Mira L. Pöhlker,
  • Sachin S. Gunthe
Subha S Raj
Indian Institute of Technology Madras, Indian Institute of Technology Madras

Corresponding Author:[email protected]

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Ovid Krüger
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Amit Sharma
Indian Institute of Technology Jodhpur, Indian Institute of Technology Jodhpur
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Upasana Panda
CSIR Institute of Minerals and Materials Technology, CSIR Institute of Minerals and Materials Technology
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Christopher Pöhlker
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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David Walter
Max-Planck-Institut für Chemie, Max-Planck-Institut für Chemie
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Jan-David Förster
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Rishi Pal Singh
India Meteorological Department New Delhi, India Meteorological Department New Delhi
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Swetha S
CSIR Fourth Paradigm Institute, CSIR Fourth Paradigm Institute
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Thomas Klimach
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Eoghan Darbyshire
The Conflict and Environment Observatory, The Conflict and Environment Observatory
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Scot T. Martin
Harvard University, Harvard University
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Gordon McFiggans
University of Manchester, University of Manchester
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Hugh Coe
University of Manchester, University of Manchester
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James D Allan
University of Manchester, University of Manchester
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Ravikrishna R
Indian Institute of Technology Madras, Indian Institute of Technology Madras
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Vijay Kumar Soni
India Meteorological Department, India Meteorological Department
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Hang Su
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Meinrat O. Andreae
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Ulrich Pöschl
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Mira L. Pöhlker
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Sachin S. Gunthe
Environmental and Water Resources Engineering Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600036, India., Environmental and Water Resources Engineering Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600036, India.
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Abstract

The Indo-Gangetic Plain (IGP) is one of the dominant sources of air pollution worldwide. During winter, the variations in planetary boundary layer (PBL) height, driven by a strong radiative thermal inversion, affect the regional air pollution dispersion. To date, measurements of aerosol-water vapour interactions, especially cloud condensation nuclei (CCN) activity, are limited in the Indian sub-continent, causing large uncertainties in the radiative forcing estimates of aerosol-cloud interactions. We present the results of a one-month field campaign (February-March 2018) in the megacity, Delhi, a significant polluter in the IGP. We measured the composition of fine particulate matter (PM1) and size-resolved CCN properties over a wide range of water vapour supersaturations. The analysis includes PBL modelling, backward trajectories, and fire spots to elucidate the influence of PBL and air mass origins on the aerosols. The aerosol properties depended strongly on the PBL height, and a simple power-law fit could parameterize the observed correlations of PM1 mass, aerosol particle number, and CCN number with PBL height, indicating PBL induced changes in aerosol accumulation. The low inorganic mass fractions, low aerosol hygroscopicity and high externally mixed weakly CCN-active particles under low PBL height (<100 m) indicated the influence of the PBL on aerosol aging processes. In contrast, aerosol properties did not depend strongly on air mass origins or wind direction, implying that the observed aerosol and CCN are from local emissions. An error function could parameterize the relationship between CCN number and supersaturation throughout the campaign.
27 Dec 2021Published in Journal of Geophysical Research: Atmospheres volume 126 issue 24. 10.1029/2021JD035681