Monthly AQI Pattern
Phnom Penh shows one of Southeast Asia's sharpest seasonal swings — nearly 3× worse in burning season versus monsoon.
Why Phnom Penh Has a Serious Air Quality Problem
Cambodia's economy has grown at 7–8% annually for two decades. Phnom Penh has transformed from a city of 1 million to 2.5 million in a generation — and its air quality has paid the price. Three converging factors create the crisis.
1. A Motorbike-Dominated Transport System
Cambodia never built a metro, bus rapid transit, or meaningful public transport. The result: 1.5 million registered motorbikes in Phnom Penh alone, the majority older carbureted engines without catalytic converters. Peak-hour congestion on National Roads 1, 2, 3, and 4 generates visible smog corridors.
2. Regional Agricultural Burning
Rice is Cambodia's primary crop, and farmers have burned straw after harvest for generations. When multiplied across the Mekong lowlands — Cambodia, southern Laos, Vietnam's Mekong Delta, northeastern Thailand — the combined fire load sends enormous smoke plumes that drift with prevailing winds into Phnom Penh's airshed from November through April.
3. Construction Boom Without Dust Controls
Phnom Penh adds thousands of buildings per year. Cambodia lacks meaningful construction dust regulations and enforcement. Major projects from Chinese and Korean investors have created a near-permanent construction haze over the city's rapidly developing districts.
Two Very Different Cities
🔥 Burning Season (Nov–Apr)
Avg AQI 125The dry season brings a double pollution punch: zero rainfall means no air washing, and agricultural fires across Cambodia, Thailand, Laos, and Vietnam fill the regional airshed with smoke. February and March are typically the worst months — AQI regularly hits Unhealthy (150+) during burning peaks. The Mekong valley geography traps smoke in low-lying Phnom Penh.
🌧️ Monsoon Season (May–Oct)
Avg AQI 59The Southwest Monsoon transforms Phnom Penh's air quality. Daily afternoon rains wash particulates from the atmosphere, and the moist air prevents burning across the region. July and August typically deliver AQI in the 'Good' range (50–60) — remarkable for a major Southeast Asian city. The wet season is Phnom Penh's window of genuinely clean air.
Pollution Sources Breakdown
Over 1.5 million registered motorbikes plus a rapidly growing car fleet produce the dominant share of PM2.5. Most bikes are older, poorly maintained carbureted engines with no catalytic converters.
Cambodia's farmers burn rice straw after harvest (Nov–Mar), while forest clearing fires across the Mekong lowlands and neighboring countries send smoke plumes into the city during dry season.
Phnom Penh is undergoing one of Southeast Asia's fastest urbanization periods. Thousands of construction sites generate coarse PM10 and fine PM2.5 year-round with minimal dust suppression.
Garment factories, food processing plants, and traditional brick kilns ringing the city burn coal and biomass, contributing to baseline pollution particularly in surrounding districts.
A significant share of Phnom Penh's population still cooks with solid fuels — charcoal and wood — adding localized PM2.5 particularly in informal settlements and peri-urban areas.
Air Quality by District
Pollution varies significantly across Phnom Penh's rapidly growing districts. Industrial and southern areas consistently record higher readings.
| District / Area | Avg AQI | Key Factor |
|---|---|---|
| Central / BKK1 / Toul Tom Poung | 108 | Dense traffic, commercial activity |
| Chamkarmon (Riverside) | 102 | Tourist area, less industrial |
| Daun Penh (Old Market area) | 115 | High traffic, old urban core |
| Meanchey / Chbar Ampov | 128 | Industrial south, landfill nearby |
| Russey Keo (North) | 118 | Brick kilns, northern approach roads |
| Sen Sok / Chip Mong area | 105 | New development, lower density |
| Airport / Pochentong | 95 | Less dense, some industrial |
Health Impact for Residents & Expats
High-Risk Groups
- 🫁 Children — lungs still developing; outdoor exposure during burning season significantly increases lifetime respiratory risk
- 🤰 Pregnant women — PM2.5 crosses placental barrier; linked to low birth weight and preterm birth
- 👴 Elderly residents — increased cardiovascular event risk during high-AQI days
- 🏃 Expat runners/cyclists — cardiovascular load during exercise multiplies PM2.5 intake; avoid morning outdoor workouts in burning season
Practical Protection
- 😷 Wear N95/KN95 during burning season (Nov–Apr); basic surgical masks don't filter PM2.5
- 🏠 Run HEPA air purifier at home — a well-sealed 20m² room can stay at good air quality even when outside is unhealthy
- 📱 Use IQAir or AirVisual app — check before leaving home; plan commutes after rain events
- 🪟 Keep windows closed on red-flag days; open in evenings during monsoon season
- 🌱 Indoor plants provide minimal filtration — invest in a real air purifier for reliable protection
Southeast Asia City Comparison
Phnom Penh sits in the middle tier of Southeast Asian capitals — cleaner than Hanoi and Jakarta, but more polluted than Bangkok and far more polluted than Singapore and Kuala Lumpur.
| City | Country | PM2.5 | Annual AQI | Notes |
|---|---|---|---|---|
| Phnom Penh ★ | Cambodia | 33 | 105 | This page ★ |
| Hanoi | Vietnam | 45 | 137 | Coal + motorbikes |
| Ho Chi Minh City | Vietnam | 38 | 120 | Traffic dominant |
| Jakarta | Indonesia | 40 | 128 | Worst large SE Asian city |
| Manila | Philippines | 35 | 110 | Traffic + open burning |
| Bangkok | Thailand | 28 | 88 | Traffic + seasonal burning |
| Kuala Lumpur | Malaysia | 18 | 62 | Relatively clean |
| Singapore | Singapore | 15 | 52 | Regional haze only risk |
What Cambodia Is Doing About Air Quality
🏛️ Ministry of Environment Monitoring
Cambodia's Ministry of Environment has deployed a small number of fixed monitoring stations in Phnom Penh, though coverage remains limited. Data is not always publicly available in real time.
⚡ Electric Vehicle Incentives
The government has begun promoting electric motorbikes with import duty reductions. Several Chinese EV brands (Dayang, Yadea, AIMA) have entered the Cambodian market. Adoption is growing but still a small share of the overall vehicle fleet.
🔥 Open Burning Restrictions
Phnom Penh city has periodic bans on open burning within city limits, but enforcement is inconsistent. The larger problem — regional agricultural burning — requires coordinated action across the Mekong sub-region that has been slow to materialize.
🌳 Green City Initiatives
Urban tree planting programs and the development of green corridors along the Tonle Sap and Mekong rivers are underway, though these have minimal impact on air quality compared to emission source controls.
Visitor's Air Quality Guide
Best Time to Visit (Air Quality)
- ✅ July–August: Cleanest air, AQI ~50
- ✅ June & September: Also very clean
- ⚠️ October–November: Transitional, acceptable
- ❌ February–March: Worst air, avoid if respiratory concerns
Travel Essentials
- 😷 Pack N95 masks if visiting Nov–Apr
- 📱 Download IQAir app before arriving
- 🏨 Book hotels with air purifiers or sealed windows
- 🚶 Riverfront walk best in early morning during monsoon
- 🛵 Tuk-tuk rides = higher exposure vs. enclosed taxi