Unraveling the Mechanism of the Holes in the Blanket of Fog Over the Indo‐Gangetic Plains: Are They Driven by Urban Heat Islands or Aerosol?

Fog holes were reported over cities of the Indo‐Gangetic plains of India, which were attributed to the urban heat island (UHI) effect. The present study reports the observational evidence of fog holes over rural area using satellite and ground observations. Delayed onset and early dissipation of fog is observed over the holes. Numerical simulations demonstrate that aerosol‐radiation interaction (ARI) leads to fog holes over both urban and rural regions. The anthropogenic aerosols and associated ARI dominate the UHI effect over the urban fog holes, while the aerosol absorption due to ARI mainly controls the rural fog holes. Turning off aerosol absorption causes ∼ 2 hours delay in the fog dissipation over urban area, whereas it yields persistent fog over rural area under saturated environment. An enhancement of soluble Aitken black carbon over the fog holes indicates the importance of aging process during fog dissipation. Plain Language Summary: This study reports the occurrence of fog holes over rural and urban regions and investigates the mechanism behind the formation of fog holes using DM‐Chem. The main reason behind the fog hole formation over Indo‐Gangetic plains is the absorption of radiation by the total black carbon aerosols. The absence of the absorbing component of aerosol‐radiation interaction leads to the occurrence of fog over both the urban and rural hole areas. The fog hole areas are correlated with an enhanced formation of small sized soluble black carbon aerosols. These findings suggest the need for detailed aging processes of carbonaceous particles in atmospheric models. Key Points: Fog holes over the rural regions reported for the first timeDelayed onset and early dissipation of fog over the hole regionsAerosol radiation effect (absorption) dominates over the urban heat island effect [ABSTRACT FROM AUTHOR]