Why Northern Vietnam Faces Severe Air Pollution at the End of the Year

Each year, from around October through April, Northern Vietnam enters its most polluted period. This pattern is not unusual — it is a seasonal trend driven by a combination of unfavorable meteorological conditions and increased emissions during the year-end months.

Unfavorable Weather Conditions: Temperature Inversion and Calm Winds

During the winter and early spring, temperature inversion and low wind speeds occur frequently. Instead of warmer air rising and dispersing pollutants, a layer of colder, denser air remains trapped near the surface. This “lid” effect prevents vertical mixing, causing fine particles to accumulate in the air closest to the ground. As a result, pollution episodes during this period are often more severe and persistent than in the summer.

Traffic – The Largest Source of Emissions

Northern Vietnam has an extremely high density of personal vehicles, particularly aging motorbikes that fail to meet emission standards. In addition to tailpipe emissions, resuspended road dust and secondary aerosol precursors significantly contribute to elevated PM2.5 levels in urban areas, especially during peak traffic hours.

Industrial Production

Major industrial zones — including coal-fired power plants, cement factories, and steel production facilities in provinces surrounding Hanoi — release substantial amounts of fine particulate pollution. Under stagnant winter meteorological conditions, these pollutants can drift into the capital, accumulate near the surface, and degrade air quality across the region.

Construction Activities and Open Burning

Construction, demolition, and unshielded material transport generate significant amounts of dust, particularly in rapidly urbanizing areas. In addition, open burning of rice straw after harvest and informal waste burning in peri-urban zones remain common, adding more pollutants to the seasonal burden.

As ecocomic activity accelerates toward the end of the year — from construction and manufacturing to transportation and goods movement — emissions tend to increase simultaneously. Combined with inversion layers and stagnant air, these factors create prolonged and severe pollution episodes that directly affect public health.

Protecting Your Health During High-Pollution Months

To reduce exposure during peak pollution season, residents are advised to:

• limit outdoor activity when AQI reaches unhealthy levels,
• keep windows closed during high-pollution hours,
• use certified masks capable of filtering ultrafine particles,
• install high-quality air purifiers to maintain clean indoor environments.

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Source: VTC News