Diwali night, indoors: 17 hours of PM2.5 in a sealed home

Patil, Shivraj

Abstract

Background. Firecrackers on Diwali night drive some of the year's highest particle pollution in Indian cities. Closing windows is the most common household response, yet little has been published on what PM2.5 inside a closed home does through the night and the morning after.

Methods. A first-generation SentioAir prototype recorded PM2.5 every 15 seconds in a closed room from 9:50 PM on 8 November 2026 to 3:00 PM on 9 November. Windows stayed shut until about 9:45 AM, then stayed open. No purifier, air conditioner or exhaust fan was used.

Results. PM2.5 peaked at 465 µg/m³ at 9:51 PM, decayed with a half-life of 3.1 to 3.5 hours, then held at 81 µg/m³ from 6:00 to 9:45 AM. After the window opened, the one-hour mean fell below India's 24-hour standard of 60 µg/m³ at 11:52 AM. The 17-hour PM2.5 sub-index was 318 (Very poor).

Conclusion. A sealed room held firecracker smoke for hours and could not clean itself below the level set by the air leaking in. When windows are closed and opened matters as much as whether they are.

At a glance

465µg/m³

Peak PM2.5, 9:51 PM

3.1 to 3.5h

Half-life, sealed room

81µg/m³

Sealed-room plateau

2 h 7min

Window open to below 60 µg/m³

318AQI

17-hour PM2.5 sub-index

99.9%

Data coverage

Key takeaways

Smoke that gets in stays in. The sealed room stayed in the Severe band for about four hours.
A sealed room clears slowly, halving its PM2.5 roughly every 3 to 3.5 hours.
Then it stops clearing, holding at about 81 µg/m³ until the window opened.
Indoors was worse than the city: 318 against 242 reported for Pune.
High-resolution data shows what daily averages hide.

Results

The prototype logged 4,112 PM2.5 readings over 17 hours 9 minutes, 99.9% of those expected. The sealed night averaged 226.8 µg/m³; the open-window afternoon averaged 40.6 µg/m³, 82% lower.

Figure 1. The full 17-hour record as two-minute mean PM2.5, with India's 24-hour standard of 60 µg/m³ and the moment the window opened.

Table 4. PM2.5 by phase (µg/m³)

Phase	Time	Mean	Median	Band
A. Sealed: smoke and decay	9:50 PM to 6:00 AM	226.8	210	Very poor
B. Sealed: plateau	6:00 to 9:45 AM	81.2	81	Moderate
C. Window open: mixing	9:45 to 10:45 AM	89.2	89.5	Moderate
D. Window open: clearing	10:45 AM to 3:00 PM	46.5	44	Satisfactory
Full record	9:50 PM to 3:00 PM	142.2	91	Very poor

Cite this paper

@techreport{patil2026diwali,
  title       = {Diwali night, indoors: 17 hours of PM2.5 in a sealed home},
  author      = {Patil, Shivraj},
  institution = {SentioAir Research, EmergeSphere Technologies Pvt. Ltd.},
  number      = {Note 01},
  address     = {Pune, India},
  year        = {2026},
  month       = nov,
  url         = {https://research.sentioair.io/publications/diwali-night-indoors}
}

References

Singh DP, Gadi R, Mandal TK, et al. Study of temporal variation in ambient air quality during Diwali festival in India. Environ Monit Assess. 2010;169(1-4):1-13.
Manchanda C, Kumar M, Singh V, et al. Chemical speciation and source apportionment of ambient PM2.5 in New Delhi before, during, and after the Diwali fireworks. Atmos Pollut Res. 2022;13(6):101428.
Shah R, Limaye S, Ujagare D, Madas S, Salvi S. Personal exposures to PM2.5 pollution during the burning of six most commonly used firecrackers in India. Lung India. 2019;36(4):324-329.

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