Hanoi Air Quality (AQI)
Vietnam · Real-time AQI, PM2.5 data, seasonal patterns & health guide
Southeast Asia's most polluted major capital. Winter peaks regularly reach AQI 150–200. Motorbike emissions + coal plants + agricultural burning combine to make Hanoi one of Asia's most challenging urban air environments.
Monthly AQI Pattern
Key Pollution Sources
| Pollutant | Annual Avg | WHO Guideline | Main Sources |
|---|---|---|---|
| PM2.5 | 26–35 μg/m³ | 5 μg/m³ | Motorbike exhaust, coal plants, agricultural burning, road dust |
| PM10 | 55–75 μg/m³ | 15 μg/m³ | Road dust, construction, industrial emissions |
| NO₂ | 35–50 μg/m³ | 10 μg/m³ | 8+ million motorbikes, traffic congestion, construction equipment |
| SO₂ | ~20 μg/m³ | 40 μg/m³ | Coal power plants (Pha Lai, Ninh Bình, Uông Bí) within 100 km |
| Ozone (O₃) | Elevated summer | 60 μg/m³ | Photochemical reactions from NOx + VOC in high-sunshine months |
The 8 Million Motorbike Problem
Hanoi has one of the world's highest motorbike-per-capita ratios — approximately 8–9 million registered motorbikes for a city of 8.5 million. During peak hours, the Old Quarter becomes a stream of motorcycles so dense that walking is faster than driving. This fleet is the dominant source of urban PM2.5, NOx, and VOCs.
Unlike car-dominated cities, motorbike engines in Vietnam are predominantly 4-stroke but many are old and poorly tuned. Two-stroke engines (still common on older bikes) produce particularly high hydrocarbon and particulate emissions. The concentration of millions of these engines in narrow Old Quarter streets with minimal ventilation creates localized AQI that frequently exceeds 200 on weekday mornings.
Air Quality by Neighborhood
Dense motorbike traffic, narrow streets that trap emissions
Heavy government vehicle traffic, central location
Lake breezes provide some relief; popular with expats
Dense residential areas, high motorbike density
Industrial areas nearby, traffic hubs
Heavy industrial activity, less urban ventilation
Seasonal Guide for Visitors & Residents
Nov – Feb (Worst)
Northeast monsoon, cold inversions, no rain to wash air. AQI 130–200. Wear N95 outdoors. Run HEPA purifier indoors.
Mar – Apr (Transitional)
Improving but dust from north. AQI 80–130. Sensitive groups should still take precautions.
Jun – Aug (Best)
Southwest monsoon + heavy rainfall. AQI 50–70. Best months for outdoor activity. Air can be genuinely clean on rainy days.
Sep – Oct (Transitional)
Rains taper, rice straw burning begins in October. AQI 68–100. Burning periods can cause sudden spikes to 150+.
Health Recommendations for Hanoi
Wear N95/KN95 during November–February
Surgical masks and cloth masks do not protect against PM2.5. During winter, AQI regularly exceeds 150 — N95 masks are essential for anyone with health concerns.
HEPA purifier in bedroom
Indoor PM2.5 in Hanoi apartments without filtration closely tracks outdoor levels. A HEPA purifier running during sleeping hours reduces your highest-exposure period significantly.
Avoid morning rush hour cycling/walking
7–9 AM in the Old Quarter is the highest-exposure period. If you must commute by bicycle or foot, mask up or reroute through side streets with less motor traffic.
Use real-time AQI monitoring
Hanoi's AQI varies enormously day-to-day. On days after heavy rain, AQI may be 40 (safe for all activities). Checking before outdoor plans is worthwhile.
Plan outdoor activities for rainy season
June–August offers Hanoi's best air quality. Time extended outdoor activities, hikes, or children's outdoor time for this window.
Frequently Asked Questions
Why is Hanoi's air quality so bad compared to Ho Chi Minh City?
Hanoi's geography is the key factor. The city sits in the Red River Delta, surrounded by mountains to the north and west. During the northeast monsoon (October–March), cold air from southern China pushes into the Red River Delta, creating temperature inversions that trap pollution near the ground. Ho Chi Minh City's more southern location and proximity to the sea gives it better atmospheric mixing. Additionally, Hanoi has more heavy industry in its surrounding provinces (coal power plants, cement, steel), while Ho Chi Minh City's surrounding provinces have lighter industrial activity.
What time of year is Hanoi's air quality worst?
November through February is consistently worst. The northeast monsoon brings cold, stable air masses that suppress vertical mixing. Combined with the city's 8+ million motorbikes, coal heating in peri-urban areas, and agricultural burning on the surrounding plains, AQI regularly exceeds 150–200 in these months. The absolute worst days often coincide with fog — Hanoi's famous winter 'mist' is largely pollution, not water vapor. PM2.5 can spike above 200 μg/m³ during these episodes.
How many motorbikes are in Hanoi?
As of 2024, Hanoi has approximately 8–9 million registered motorbikes for a population of about 8.5 million people — roughly one per resident. Vietnam's motorbike culture is the primary source of PM2.5, NOx, and volatile organic compounds (VOCs). The city has announced plans to ban motorbikes from the urban core by 2030, but implementation faces massive social and economic challenges since motorbikes are essential transport for millions of residents.
Does rice straw burning affect Hanoi's air quality?
Significantly, during specific periods. After rice harvests (typically May–June and October–November), farmers in the Red River Delta burn rice straw in the fields surrounding Hanoi. During these burning periods, PM2.5 can spike 2–3× above baseline. Satellite imagery clearly shows agricultural burning halos around Hanoi during harvest seasons. The Vietnamese government has banned open agricultural burning multiple times, but enforcement remains limited.
Is there a clean season in Hanoi?
June and July are the cleanest months. The southwest monsoon brings substantial rainfall (Hanoi receives 1,600–1,800 mm annually, mostly May–September), which efficiently washes PM2.5 from the atmosphere. On rainy days in July, AQI in Hanoi can drop to 30–50 — genuinely clean air. If you're sensitive to air quality and visiting Hanoi, July is the optimal month.