Delhi's AQI crossed 300 this week as stubble burning's share of the city's smoke climbed to about 18.5%, up from about 5% a day earlier. A 2025 study of 441 Thai motorcycle taxi drivers found something riders should sit with: a driver's own personal PAH exposure did not predict their chronic bronchitis risk. Their province's average PAH level did.
That means the "moderate" reading on your phone can miss the exact exposure pattern linked to bronchitis, because the number that matters is not about you. It is about the air over your whole region.
Smoke sits low over Delhi's flyovers this morning, thick enough that commuters are pulling their visors down before they clear their own driveway. The city's AQI hit 307 at 7am today, its worst reading in months, with Diwali six days away (Business Standard, 2026).
Stubble burning's share of that smoke climbed to about 18.5% in the government's most recent Decision Support System reading, up from about 5% the day before (Outlook India, 2026; NewsBytes, 2026).
Here is the gap nobody is riding around. A phone showing "moderate" during a stubble burning spike is not lying. It is measuring the wrong thing entirely, and a new study on motorcycle riders just proved it.
Key takeaways
- Delhi's AQI hit 307 this week, with stubble burning's share of the smoke climbing to about 18.5% from about 5% the day before (Business Standard, 2026; Outlook India, 2026).
- Among 441 Thai motorcycle taxi drivers, a driver's own PAH exposure did not predict their bronchitis risk, but their province's average PAH level did (Samana et al., 2025).
- Satellite data show Punjab and Haryana fire counts explain 78% of Delhi's smoke-haze variance each Oct and Nov, with about 60% of that smoke arriving within 36 hours (Kotrike & Sridhar, 2026).
- Punjab's rice-residue burning area grew from about 0.26 million to 3.14 million hectares between 2000 and 2020, the fuel load behind the whole pattern (Romana et al., 2026).
The research behind this
Peer-reviewed and official measurements this post is built on. Each card says what was measured, what was found, and what it cannot tell you.
Thai motorcycle-taxi PAH and bronchitis
- What they measured
- 441 motorcycle taxi drivers across 6 central Thai provinces, personal PM2.5 and PM10 samplers, 15 PAH compounds measured by lab chromatography.
- What they found
- A driver's own PAH exposure did not predict their lung function or bronchitis symptoms. Their province's average PM10-bound PAH level was positively correlated with the share of drivers reporting chronic bronchitis.
- What it can't tell you
- Self-reported bronchitis, not a physician diagnosis, and a cross-sectional design that cannot prove cause.
Bangkok motorcycle-taxi lung function
- What they measured
- 1,283 motorcycle taxi drivers against 600 enclosed-vehicle taxi drivers in Bangkok, spirometry compared against modelled PM10 exposure.
- What they found
- Motorcycle drivers at 50 ug/m3 PM10 or above had a significantly lower FEV1/FVC ratio than drivers at lower exposure.
- What it can't tell you
- PM10 came from area monitors, not personal samplers, and the design cannot separate pollution from other job factors.
Satellite link: Punjab fires to Delhi haze
- What they measured
- MODIS and VIIRS fire counts across Punjab and Haryana plus forward air-mass trajectories into Delhi, 2020 to 2024, Oct and Nov windows.
- What they found
- Daily fire counts explained 78% of Delhi's aerosol haze variance in Oct and Nov. About 60% of trajectories from active-burn zones reached Delhi within 36 hours.
- What it can't tell you
- The measure is a satellite haze proxy, not a ground PM2.5 or PAH reading, and no health outcome was tested.
Crop burning and child mortality, South Asia
- What they measured
- A decade of satellite fire data, wind direction, and health survey data across India and Pakistan.
- What they found
- Crop burning accounts for 40 to 60% of peak winter pollution. A log-unit increase in in-utero exposure to burning-related pollution raised child mortality by 30 to 36 deaths per 1,000 births.
- What it can't tell you
- The result is population-level across South Asia, not specific to motorcycle riders, and relies on a wind-direction instrument rather than direct dose.
What the studies actually measured
The Thai study is the one worth sitting with. Researchers fitted personal air samplers to 441 motorcycle taxi drivers across 6 provinces around Bangkok, then measured 15 PAH compounds in each sample by lab chromatography (Samana et al., 2025).
PAH stands for polycyclic aromatic hydrocarbons, a carcinogenic class of chemicals that forms specifically from burning biomass and fuel, not from dust or road wear.
The province of Pathum Thani averaged PM2.5-bound PAH of 36.9 ng/m³, well above the other five provinces (Samana et al., 2025).
When the researchers checked which number predicted chronic bronchitis in drivers, the individual driver's own PAH reading showed no meaningful link. The province's average PAH level did.
That points at something uncomfortable. A rider cannot out-ride a bad airshed by having a slightly better commute than their neighbor. The risk tracks the region's combustion chemistry, not the individual's personal exposure count.
Two more studies back up pieces of this picture. In Bangkok, drivers exposed to higher PM10 had a measurably lower FEV1/FVC ratio than drivers in enclosed taxis, a pattern visible even with area-level pollution data (Arphorn et al., 2018).
And in Delhi's own airshed, satellite tracking shows Punjab's fires explain most of the Oct and Nov haze swing, with smoke reaching the city in about a day and a half (Kotrike & Sridhar, 2026).
Ride with filtered air
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How Punjab's burning season became Delhi's winter problem
Every October and November, farmers across Punjab and Haryana burn the leftover rice stalks from the harvest to clear fields fast for the next planting. It is cheap and quick, and the practice has grown with the crop.
Punjab's rice cultivation area expanded from about 0.26 million hectares to 3.14 million hectares between 2000 and 2020, roughly a twelvefold increase in the raw fuel load for stubble burning (Romana et al., 2026).
More rice means more residue, and more residue means more smoke each winter.
That smoke does not stay in Punjab. Satellite tracking of daily fire counts against Delhi's haze levels shows the fires explain 78% of the city's Oct and Nov smoke variance, and about 60% of the smoke from active-burn zones reaches Delhi within 36 hours (Kotrike & Sridhar, 2026).
Zoom out across South Asia and the pattern holds at scale. Crop burning accounts for 40 to 60% of peak winter pollution across the region, and researchers have tied in-utero exposure during burning season to higher infant mortality (Dipoppa & Gulzar, 2024).
Treat the first week of November as filter weather in Delhi-NCR regardless of what your app says. The fuel load is already in the field, and the transport time to your street is about a day and a half.
The number on your phone is measuring the wrong thing
A standard AQI reading is built from PM2.5 and PM10 mass alone. It weighs a gram of smoke the same as a gram of road dust, even though they are chemically nothing alike. One is mostly carbon soot and biomass PAH. The other is mostly crustal grit.
That is the first gap, and it is not new. What the Thai motorcycle-taxi study adds is a second, sharper gap. Even a monitor reading the right pollutant, personally, on your own body, still would not predict your risk. The number that mattered in that study was the province's average, not the driver's own count.
- About 18.5% of Delhi's PM2.5 is attributed to stubble burning in the most recent reading, up from about 5% the day before (Outlook India, 2026).
- The rest comes from traffic, construction dust, and other winter sources already in the city's air.
| Reading | Share attributed to stubble burning |
|---|---|
| Day before | about 5% |
| Most recent | about 18.5% |
Passive helmet vents, the mesh and slots built into most helmets, filter nothing by chemistry. They pass a PAH-heavy biomass particle exactly as easily as any other particle of the same size. During a stubble burning spike, the mix skews harder toward PAH specifically, and a vent cannot tell the difference.
Why the fuel upwind matters more than the reading on your phone
What riders' health could look like by 2031
No source gives a direct number for rider exposure in 2031, so this section is a synthesis, built from two real papers and labeled as such rather than stated as fact.
If Punjab's rice-residue area keeps growing anywhere near its 2000 to 2020 pace, roughly 6% a year compounded, the fuel load behind each burning season keeps rising (Romana et al., 2026).
Layer that against the high-haze window Kotrike and Sridhar measured, currently about 4 to 6 weeks each Oct and Nov with 78% of the variance explained by fire counts (Kotrike & Sridhar, 2026).
Extend both trends out five years and the window plausibly widens toward 6 to 8 weeks by 2031. That would mean roughly 50% more high-PAH riding days per season for Delhi-NCR riders than today, using the same province-level exposure logic the Thai study established.
Filtering the thing the AQI number can't see
Easi Breezi pulls air through H11 HEPA media directly at the rider's face, stopping at least 95% of PM2.5 by size, not by chemistry. It does not need to know a particle is PAH-bound to stop it, which is exactly the blind spot a personal AQI reading has during a stubble burning spike.
See the clip-on helmet air purifier and check current conditions on the live haze page.
What stubble burning means for motorcycle riders this week
Delhi's stubble burning share is climbing into a holiday week with fireworks on top. None of the four steps below need a perfect AQI reading to be worth doing.
- Do not trust a single personal reading. The Thai study found a driver's own PAH number did not predict their bronchitis risk (Samana et al., 2025).
- Check the regional trend, not just one number. Stubble burning's share moved from about 5% to about 18.5% in a single day in the most recent DSS reading (Outlook India, 2026).
- Expect the smoke to lag the fires by about a day and a half. Punjab's fires explain most of Delhi's haze swing on roughly that delay (Kotrike & Sridhar, 2026).
- Filter by particle size, not by reading. The Easi Breezi clip-on air purifier stops PM2.5 at the intake regardless of its chemistry.
Frequently asked questions
Does a bad personal AQI reading predict a rider's bronchitis risk?
Not on its own. A 2025 study of 441 Thai motorcycle taxi drivers found an individual's own PAH exposure did not predict their bronchitis symptoms. Their province's average PAH level did (Samana et al., 2025).
Why is Delhi's AQI so high right now?
Delhi's AQI hit 307 this week as stubble burning's share of the city's PM2.5 climbed to about 18.5% from about 5% the day before, ahead of Diwali on Nov 8 (Business Standard, 2026; Outlook India, 2026).
How fast does Punjab's smoke reach Delhi?
About 60% of smoke from the active-burn zones in Punjab and Haryana reaches Delhi within 36 hours, and fire counts there explain 78% of Delhi's Oct and Nov haze swing (Kotrike & Sridhar, 2026).
Does a motorcycle helmet air filter help against stubble burning smoke?
Easi Breezi's H11 HEPA media is rated to stop at least 95% of PM2.5 by particle size, which includes PAH-bound particles from biomass smoke. It does not remove gases such as carbon monoxide.
Sources
- Samana, P., Ito, K., Suthienkul, O., Ketsakorn, A. and colleagues (2025). "Analysis of PM-bound polycyclic aromatic hydrocarbons exposure among motorcycle taxi drivers in six central provinces in Thailand in winter." PLOS ONE 20(12):e0336587. doi.org/10.1371/journal.pone.0336587
- Arphorn, S., Ishimaru, T., Hara, K., Mahasandana, S. (2018). "Considering the effects of ambient particulate matter on the lung function of motorcycle taxi drivers in Bangkok, Thailand." Journal of the Air & Waste Management Association 68(2):139-145. doi.org/10.1080/10962247.2017.1359217
- Kotrike, T., Sridhar, V. (2026). "Tracing the haze: satellite-based assessment of stubble burning and air quality in Delhi." Air Quality, Atmosphere & Health 19(1):9. doi.org/10.1007/s11869-026-01885-x
- Dipoppa, G., Gulzar, S. (2024). "Bureaucrat incentives reduce crop burning and child mortality in South Asia." Nature 634:1125-1131. doi.org/10.1038/s41586-024-08046-z
- Romana, H.K., Shukla, D.P., Singh, R.P. (2026). "Long-term variability of air quality and greenhouse gas emissions from rice crop burning in Punjab during 2012-2020." RSC Advances 16:13304-13319. doi.org/10.1039/d5ra09439a
- Outlook India (2026). "Delhi AQI today: air quality, pollution forecast ahead of Diwali." outlookindia.com
- Business Standard (2026). "New winter curbs kick in but Delhi chokes as AQI very poor zone at 307." 2 November. business-standard.com
Written by Ash, mechanical engineer and founder of Easi Breezi, building an active HEPA filtration system for motorcycle helmets (Patent Pending). Based between Hong Kong and Bali, riding daily in the traffic this blog writes about.