Severe air pollution in New Delhi, India's capital, and the surrounding plains worsened further as smoke from celebratory firecrackers and fireworks filled the air during Diwali, Hinduism's largest festival, also known as the Festival of Lights. Combined with early-winter weather conditions, including radiative cooling and calm winds, the smoke contributed to a blanket of dense fog containing harmful pollutants across the city. At Indira Gandhi International Airport (VIDP/DEL), surface visibility briefly plunged to 350 m in the pre-dawn and early-morning hours of the 9th, affecting aircraft operations.
Diwali Fireworks Trigger a Sharp Deterioration in Air Quality
Despite local authorities' bans and restrictions on fireworks and firecrackers, they were set off in many areas during Diwali. Around November each year, New Delhi and its surrounding areas experience a seasonal peak in air pollution as crop-residue burning, industrial emissions and vehicle exhaust combine. The large volume of smoke released during the festival intensified the pollution, sending concentrations of fine particulate matter, including PM2.5, soaring to dangerous levels.
How Weather Conditions and Air Pollution Combined to Produce Dense Fog
Several factors contributed to the formation of dense fog:
・Radiative Cooling, Surface High, and Stable Atmospheric Conditions
Under the control of a surface high-pressure system, clear skies and overnight radiative cooling chilled the air near the ground, establishing a sharp surface-based temperature inversion. Meanwhile, calm to very light winds of 0–2 knots created stagnant weather conditions, severely suppressing atmospheric dispersion and causing pollutants to accumulate near the surface.
・Increased Condensation Nuclei and Fog Development
In the relatively humid conditions—an air temperature of 19°C, a dew point of 17°C and a relative humidity of approximately 88%—fine particles from fireworks smoke and other sources are thought to have acted as condensation nuclei, providing surfaces on which water vapor could condense and promoting the rapid development of fog containing pollutants.
Visibility Falls to 350 m at Indira Gandhi International Airport (VIDP/DEL)
Surface visibility deteriorated significantly at Indira Gandhi International Airport (VIDP/DEL), New Delhi's main air gateway.
Deterioration: Late on the 8th to the Pre-Dawn Hours of the 9th
Local time: 23:30–04:00 / UTC: 18:00–22:30
With winds remaining calm to very light at 0–2 kt, visibility gradually fell from 1,200 m, with mist (BR), to 600–500 m. Shallow fog (MIFG) was observed.
Peak Dense Fog: Early Morning on the 9th
Local time: 05:00–08:00 / UTC: 23:30 on the 8th–02:30 on the 9th
Calm winds of 0 kt or very light winds of 2 kt persisted, and surface visibility fell to 350–400 m, with fog (FG) reported. Runway visual range (RVR) also dropped to a minimum of 350 m on Runway 09 and 500 m on Runway 10.
Recovery and Haze: Morning to Mid-Morning on the 9th
Local time: 08:30–10:00 / UTC: 03:00–04:30
As sunshine raised the temperature from 18°C to 24°C and easterly winds of 3–6 kt developed, the fog gradually dissipated. Visibility improved from 600 m, with shallow fog (MIFG), to 1,500 m, while RVR on all runways recovered to 2,000 m or more.
However, pollutants remained in the air after the fog cleared, and the reported weather phenomenon changed to haze (HZ).
VIDP 090430Z 12006KT 1500 R10/2000 R09/2000 R11L/2000 R11R/2000 HZ NSC 24/18 Q1021 NOSIG=
VIDP 090400Z 09005KT 1200 R10/2000 R09/2000 R11L/2000 R11R/2000 HZ NSC 23/18 Q1020 BECMG 1500 HZ=
VIDP 090330Z 11004KT 0900 R10/2000 R09/1700 R11L/2000 R11R/1900 MIFG NSC 22/18 Q1020 BECMG 1500 HZ=
VIDP 090300Z 10003KT 0600 R10/2000 R09/0800 R11L/1900 R11R/1600 MIFG NSC 21/18 Q1020 BECMG 0800 MIFG=
VIDP 090230Z VRB02KT 0400 R10/1200 R09/0400 R11L/1400 R11R/1300 FG NSC 20/17 Q1019 BECMG 0600 MIFG=
VIDP 090200Z VRB02KT 0400 R10/1100 R09/0400 R11L/1400 R11R/1100 FG NSC 20/17 Q1019 BECMG 0600 MIFG=
VIDP 090130Z 00000KT 0400 R10/0550 R09/0400 R11L/1100 R11R/0900 FG NSC 19/17 Q1019 NOSIG=
VIDP 090100Z VRB02KT 0400 R10/0600 R09/0400 R11L/1700 R11R/1000 FG NSC 18/16 Q1018 NOSIG=
VIDP 090030Z 00000KT 0350 R10/0800 R09/0375 R11L/1800 R11R/0800 FG NSC 18/16 Q1018 NOSIG=
VIDP 090000Z 00000KT 0350 R10/0500 R09/0350 R11L/1400 R11R/0750 FG NSC 19/17 Q1018 NOSIG=
VIDP 082330Z 00000KT 0350 R10/0550 R09/0350 R11L/1000 R11R/0700 FG NSC 19/17 Q1017 NOSIG=
VIDP 082300Z 00000KT 0500 R10/0650 R09/0500 R11L/0900 R11R/0750 MIFG NSC 19/17 Q1017 TEMPO 0350 FG=
VIDP 082230Z 00000KT 0500 R10/0700 R09/0650 R11L/0900 R11R/0800 MIFG NSC 19/17 Q1017 TEMPO 0350 FG=
VIDP 082200Z 00000KT 0600 R10/0800 R09/0650 R11L/1000 R11R/0900 MIFG NSC 19/17 Q1017 NOSIG=
VIDP 082130Z VRB02KT 0600 R10/0800 R09/0700 R11L/1400 R11R/0650 MIFG NSC 20/17 Q1017 NOSIG=
VIDP 082100Z VRB02KT 0600 R10/1000 R09/0700 R11L/1000 R11R/0600 MIFG NSC 21/16 Q1017 NOSIG=
VIDP 082030Z VRB02KT 0600 R10/0900 R09/0700 R11L/1100 R11R/0800 MIFG NSC 21/17 Q1018 NOSIG=
VIDP 082000Z VRB02KT 0600 R10/1000 R09/0800 R11L/1000 R11R/0800 MIFG NSC 21/17 Q1018 NOSIG=
VIDP 081930Z VRB02KT 0600 R10/1100 R09/1100 R11L/1300 R11R/0800 MIFG NSC 21/17 Q1018 NOSIG=
VIDP 081900Z 07003KT 0700 R10/1200 R09/0900 R11L/1200 R11R/0800 MIFG NSC 21/17 Q1018 BECMG 0600 MIFG=
VIDP 081830Z VRB02KT 0900 R10/1300 R09/1100 R11L/1200 R11R/1000 MIFG NSC 21/17 Q1018 BECMG 0800 MIFG=
VIDP 081800Z VRB02KT 1200 R10/1700 R09/1300 R11L/1200 R11R/1200 BR NSC 21/17 Q1018 NOSIG=
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