Urban Heat Island Over Delhi Punches Holes in Widespread Fog in the Indo‐Gangetic Plains

Abstract

Persistent and widespread fog affects several densely populated and agriculturally fertile basins around the world. Dense and polluted fog is especially known to impact transportation, air quality, and public health. Here we report a striking observation of holes in fog over urban areas in satellite imagery. The extent of fog holes appear highly correlated with city populations in fog‐prevalent regions of Asia, Europe, and the United States. We find the highest frequency and largest extent of fog holes over Delhi along with suppressed fog fraction, amidst increased fog occurrence over the Indo‐Gangetic Plains, based on 17 years of satellite data (2000–2016). This apparent urban heat impact is characterized in sharp urban‐rural gradients in surface temperatures and fog thickness. Urban heating seems to have already amplified the long‐term fog decline in Europe and the United States and should be assessed over regions undergoing urban expansion including India, where no previous linkages are reported between urban heating and fog.

Contribution of Hydroxymethane Sulfonate to Ambient Particulate Matter: A Potential Explanation for High Particulate Sulfur During Severe Winter Haze in Beijing

“…Such transient depletions do show up in observations for winter 2014, but not concurrently with large increases in PM 2.5 (Rao et al, ). We hypothesize that factors unaccounted for in the model—for example, spatial heterogeneity in clouds (Gautam & Singh, ), horizontal transport, or feedbacks between haze and boundary layer height (Ding et al, ; Li et al, )—could slow the depletion of surface HCHO such that the clouds disappear before significant drawdown of surface HCHO. This issue could be further investigated with a 3‐D chemical transport model.…”

Driving Factors of Aerosol Properties Over the Foothills of Central Himalayas Based on 8.5 Years Continuous Measurements

“…Considering the diverse fossil fuel use for domestic, industrial, and transport energy, and the open waste burning for disposal and heating purposes in this region (CPCB, ), especially over the IGP, the postmonsoon and winter seasons have also witnessed high pollution levels (Chakraborty et al, ; Hooda et al, ; Hyvärinen et al, ; Komppula et al, ). The elevated wintertime pollution levels as well as severe anthropogenic winter haze (Sati & Mohan, ) further coincide with the fog period (Ganguly et al, ; Gautam et al, ; Gautam & Singh, ), resulting in manifold increases in the complexity of aerosol composition over the region. These spatiotemporally diversified emissions are coupled with varying atmospheric dynamics, such as contrasting monsoons and varying ABL.…”

Effect of Reduced Summer Cloud Shading on Evaporative Demand and Wildfire in Coastal Southern California

“…These trends are strongest in the greater Los Angeles and San Diego areas and appear largely driven by the urban heat island effect and background anthropogenic greenhouse warming (Williams, Schwartz, et al, ). Warming forces the altitude of condensation to rise and increases the frequency of cloud‐free conditions when saturation is not achieved within the boundary layer (Gautam & Singh, ; Gentine et al, ; Lin et al, ; O'Brien, ; Wood, ).…”

“…These trends are strongest in the greater Los Angeles and San Diego areas and appear largely driven by the urban heat island effect and background anthropogenic greenhouse warming (Williams, Schwartz, et al, 2015). Warming forces the altitude of condensation to rise and increases the frequency of cloud-free conditions when saturation is not achieved within the boundary layer (Gautam & Singh, 2018;Gentine et al, 2013;Lin et al, 2009;O'Brien, 2011;Wood, 2012). Williams, Schwartz, et al (2015) speculated that as a result of reduced warm-season cloud shading, increased solar radiation at the surface has enhanced the evaporative demand and decreased fuel moisture on the vegetated mountains that ring the large coastal cities of CA.…”