Nakhon Ratchasima — known locally as Korat — is the gateway to Isaan, sitting on the flat Khorat Plateau surrounded by sugarcane and rice farmland. From roughly December to April, field-clearing burns across the plateau push PM2.5 up. Here's the month-by-month picture, plus the purifiers, masks and apps residents rely on.
Air quality is a genuine but seasonal consideration in Nakhon Ratchasima, not the dominant factor it is further north in Chiang Mai. For roughly seven months of the year — May through November — the Khorat Plateau enjoys clean, monsoon-fresh air. But during the December–April dry season, peaking around February–March, sugarcane and rice-stubble burning across Korat and the wider Isaan region push PM2.5 into the moderate-to-unhealthy-for-sensitive range on still, dry days. The flat, open terrain of the plateau disperses smoke more readily than Chiang Mai's mountain-ringed valley, so Korat rarely sees the extreme spikes the north gets — but sensitive residents, families with young children and anyone with respiratory conditions should still plan around it. For the wider seasonal picture, see the flood risk & monsoon guide; for daily life basics, the Nakhon Ratchasima hub.
Typical air-quality pattern through the year, using the US AQI scale and approximate PM2.5 (µg/m³) ranges. Any given year varies with rainfall, wind and the intensity of the sugarcane and rice-stubble burning — but the shape is fairly consistent.
| Month | Typical AQI band | PM2.5 (µg/m³) | Status | What to expect |
|---|---|---|---|---|
| January | Moderate | ~35–70 | Dry season sets in | Cool, dry air with agricultural smoke building as the sugarcane and rice harvest gets underway across the Khorat Plateau. |
| February | Moderate–USG | ~50–100 | Burning season builds | Field-clearing burns intensify across Korat and neighbouring Isaan provinces; readings push toward 100 on still, dry days. |
| March | Unhealthy for Sensitive (peak) | ~65–130 | Worst month | The peak of the plateau's burning season, with regional haze from Korat's own fields plus drift from surrounding provinces. |
| April | Moderate–USG | ~45–95 | Still hazy, easing late | Hot and often smoky through the first half; early pre-monsoon storms start clearing the air by late April. |
| May | Moderate → Good | ~25–55 | Monsoon arrives | The rains wash out the haze within days of the first real downpours. |
| June | Good | ~15–40 | Clean | Green, rainy and clean, with only brief hazy spells between storms. |
| July | Good | ~12–35 | Clean | Reliably clean monsoon air across the plateau. |
| August | Good | ~10–30 | Cleanest | One of the freshest months of the year for air quality. |
| September | Good | ~10–30 | Cleanest | Peak monsoon rainfall keeps the air about as clean as Korat gets. |
| October | Good → Moderate | ~15–40 | Clean, tailing off | Monsoon eases with clear, green post-rain conditions lasting most of the month. |
| November | Moderate | ~20–50 | Cool & mostly clean | Cool-season skies are mostly clear, though the first dry-season haze can creep in late in the month. |
| December | Moderate | ~30–65 | Dry season & burning begin | The dry season takes hold and early field-clearing fires start pushing readings up ahead of the January–March peak. |
US AQI: 0-50 good · 51-100 moderate · 101-150 unhealthy for sensitive · 151-200 unhealthy · 201-300 very unhealthy · 300+ hazardous.
Each year from roughly December to April, farmers across Nakhon Ratchasima and the wider Khorat Plateau — one of Thailand's largest sugarcane and rice-growing regions — burn crop residue to clear fields quickly and cheaply ahead of the next planting. Korat sits low and flat, ringed by farmland rather than mountains, so smoke doesn't accumulate in a trapped valley the way it does in Chiang Mai — but on still, dry, windless days it can settle over the city and outlying districts, and regional haze drifting from neighbouring Isaan provinces and even greater Bangkok adds to the load. The peak typically lands in February and March, when dry-season conditions and burning both hit their height. The first monsoon rains in May reliably wash the haze out within days.
Short-term exposure to elevated PM2.5 commonly causes irritated eyes, a scratchy throat, coughing, headaches and worsened allergies. It is hardest on children, the elderly, pregnant women and anyone with asthma or existing lung or heart conditions. Korat's dry-season readings are generally less severe than Chiang Mai's, but families with vulnerable members should still track daily AQI during December–April and keep a purifier and masks on hand. For local hospitals and clinics, see Nakhon Ratchasima healthcare.
A HEPA air purifier for the bedroom is the single most effective thing a sensitive household can do. Size it to the room (check the CADR — clean-air delivery rate) and run it through the haziest months. Approximate Thailand prices:
| Option | Price (THB) | Best for | Notes |
|---|---|---|---|
| DIY box-fan + HEPA (Corsi–Rosenthal) | ~1,500–2,500 | Bedrooms on a budget | A box fan taped to one or more HEPA filters. Cheap and surprisingly effective; filters are the main running cost. |
| Xiaomi / Mi Air Purifier 4 Lite / 4 | ~3,500–7,000 | Bedrooms & small living rooms | The default value pick for most Korat rentals — real HEPA, an app, and a live PM2.5 display for a single room. |
| Philips / Sharp mid-range | ~8,000–16,000 | Larger living rooms & houses | Higher CADR for the open-plan houses common in Korat's suburbs and satellite towns. |
| Blueair / IQAir / premium | ~20,000–55,000+ | Whole-home / sensitive lungs | Top-tier filtration for those with asthma or young children, or anyone wanting a sealed 'clean room' during peak burning weeks. |
Prices are indicative and vary by retailer and promotion (Lazada, Shopee, Power Buy, HomePro).
For outdoor protection, only a properly fitted N95, KN95 or FFP2 respirator filters fine PM2.5 — ordinary cloth and surgical masks do little. A good mask seals snugly around the nose and cheeks; facial hair breaks the seal. They are inexpensive and widely available in pharmacies, convenience stores and on Lazada and Shopee. Worth keeping a few on hand for the February–March peak, especially if you're near the sugarcane-growing districts on the city's outskirts.
Checking the AQI becomes a quick daily habit through the haziest months. These are the tools residents rely on:
Live AQI, PM2.5 and a 3-day forecast, with a global city-ranking useful for comparing Korat against Bangkok and the north during the worst weeks.
The official app and site from Thailand's Pollution Control Department, with government monitoring stations covering the Khorat Plateau — the authoritative local source for Korat readings.
A free web map aggregating stations worldwide; useful for comparing Korat against Bangkok, other Isaan provinces and the north at a glance.
Google, Apple Weather and similar now surface an AQI figure — fine for a quick glance, but the dedicated apps above are more accurate and give forecasts.
Korat's seasonal pattern tracks close to Bangkok's, since both sit on relatively flat terrain and share regional haze sources — moderate air most of the year with a December–April dip. It is meaningfully better than Chiang Mai, where mountains trap smoke in a valley and AQI can spike into very unhealthy territory each March. It doesn't match the near-year-round clean air of the southern islands and beaches. For those weighing locations partly on air quality, compare options on our compare cities tool.
For most of the year, no — from May to November the Khorat Plateau enjoys clean, monsoon-fresh air. But roughly December to April, and especially February to March, Korat sees a real drop in air quality driven by sugarcane and rice-stubble field-clearing burns across the surrounding Isaan provinces. It's generally less extreme than Chiang Mai's mountain-trapped burning season, but noticeably worse than the southern coast and islands.
Roughly December through April, with the worst readings typically in February and March. Farmers across the Khorat Plateau — one of Thailand's largest sugarcane and rice-growing regions — burn crop residue to clear fields quickly and cheaply ahead of the next planting.
Korat generally tracks close to Bangkok's seasonal pattern — moderate for most of the year with a December–April dip — since both sit on relatively flat terrain. It is typically less severe than Chiang Mai, where mountains trap smoke in a valley and AQI can spike higher each March.
On the US AQI scale, 0–50 is good and 51–100 moderate; 101–150 is unhealthy for sensitive groups, 151–200 unhealthy for everyone. Korat's worst days, typically in February–March, tend to sit in the unhealthy-for-sensitive range — this is when masks, purifiers and limiting outdoor time matter most.
If you're sensitive to smoke, have young children, or plan to live there year-round, a HEPA purifier for the bedroom is a sound investment for December–April. A budget Xiaomi unit (roughly 3,500–7,000 THB) covers a single room well.
Only a properly fitted N95, KN95 or FFP2 respirator filters fine PM2.5 particles — cloth and standard surgical masks do not. Keep a few on hand for the worst weeks of February and March.
Primary and official sources are cited above. Government rules, fees and procedures in Thailand change over time and vary by office; always confirm current requirements with the relevant authority before relying on them. BAANLYY never takes paid placement in editorial content.
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Hero photo by HUAHIN PILOT LAND & REAL ESTATE DRONER on Pexels. General information, not medical advice; confirm current readings with official sources before making health decisions.