Hanoi: Winter, the most polluted season

Hanoi in the east, along the main traffic routes, each hour, has more than 0.3 milligrams of PM10 dust (dust less than 10 microns in size) crawling into people's lungs. Winter is also the period when Hanoi is most polluted.

PM10 are dust particles of less than 10 microns (1 micron = 1 / 1,000 mm), capable of penetrating deep into the lungs, harming the respiratory and cardiovascular systems. Other pollutants such as SO ₂ , NO ₂ , CO and O ₃ (ozone) also increased, some of which could exceed the permitted standards in many parts of the city.

Status and causes

Currently, the capital of Vietnam is an address of "air pollution" in the world.

Recalling Hanoi 10-15 years ago, it can be seen right away that this is the consequence of the process of urbanization, lack of control and one-way economic growth, lack of environmental protection solutions. Accidentally or deliberately, we followed the slogan: " Growth above all, aftermath environment " (Growth first, environment later).

Time to be able to leave later! Too much gasoline, oil and coal are pumped into the economic vehicle and then thrown into the atmosphere of a large amount of pollutants. Meanwhile, in many neighborhoods, people and motor vehicles have to squeeze together so that there is not enough space for them to spread before people breathe into the lungs.

The amount of traffic has far surpassed the capacity of infrastructure.

At the main traffic routes, PM10 dust increases in winter (Photo: VNN)

The overwhelming street motorcycles cause constant traffic jams that create many "contaminated hot spots" PM10, NO2, and benzene on the map. If most motorcycles are replaced by public transport, both fuel and pollution emissions will be greatly reduced.

The road surface is too dirty, the sandy soil by the vehicle speeds up makes up an important component in PM10 dust. Use of sulfur-rich coal and oil, making SO ₂ gas rise in many industrial and residential areas.

Studies in recent years by domestic and foreign authors show that Hanoi is also affected by coal-fired thermal power plants in surrounding areas. Pollutants from the other side of the border also follow northeast monsoon air masses that bring to Hanoi and surrounding areas a large amount of polluted gas and tiny particles of less than 2.5 microns (PM2 , 5).

Two questions: when and where?

Hanoi's air is generally heavily polluted, but luckily, not always. Pollution levels always fluctuate with meteorological factors such as wind, rain, air humidity, sunlight, and especially the level of mixing of the atmosphere.

It can be said that with the same emission level, air pollution will be greatly reduced when there is strong wind, heavy rain and strong disturbance atmosphere (high smoke smoke from the factory chimneys). These weather conditions are dominated by the nature and path of monsoon winds affecting the northern part of our country.

No one can control the above weather phenomena. But while the global solutions have not been implemented to solve the air pollution in Hanoi, it is necessary to grasp the rules of pollution according to the weather, especially before the air is polluted. heaviest, is extremely necessary.

Winter and heat-induced heat radiation (nocturnal radiation temperature inversion)

This phenomenon is very recognizable.From October to the middle of January, a few days after the northeast monsoon winds come, the weather becomes dry, the sky is clear, the sun is beautiful, the northeast light wind is cold, the night is cold and the wind is still close until late ., but the dust is visible under electric lights and car headlights on the road.The ground is heated by sunlight all day, cold at night by emitting infrared radiation, the air temperature near the ground will therefore increase with altitude until about 150-200 meters, then new. reduced as "usual".Detective radio balls do not drop in the Meteorological Garden At this time every 6 pm, this phenomenon was recorded on the right days with the highest levels of pollution between two successive monsoon winds in the dry season.

Environmental management agencies will be able to implement measures to limit emissions, while the elderly, children, people with respiratory and cardiovascular diseases will have a proactive way to prevent it.

This is the most expensive lesson from the historical disaster of air pollution, causing more than 4,000 Londoners to die in the late fog of December 1954.

The following rules are drawn from the air quality monitoring (CLKK) systematically at Lang Meteorological Garden conducted by the Hydrometeorological Center of the Northern Delta Region (TT KTTV). since 2001 and Vietnam Atomic Energy Institute (VNLNT) since 1998.

The law of weather changes of pollutants in other places within Hanoi is similar to Lang Garden Meteorological Garden. But the level of pollution in other places may be higher or lower in Lang Meteorological Park, depending on the amount of emissions and the ability to disperse pollutants there. This is the second question: Where is the air heavily polluted?

The Swiss-Vietnamese Clean Air Program (SVCAP) in collaboration with the Hanoi Center for Environmental and Resource Monitoring and Analysis (CENMA) sought to answer this question through two passive gas sampling campaigns. (passive sampling) in the winter and summer of 2007 at 120 locations, focusing mainly on 8 urban districts. Hopefully, this research result will be officially announced one day.

To answer the first question (when), please read some diagrams to record monitoring results at Lang Meteorological Garden below. For scientific explanation, readers can refer to (http://www.tchdkh.org.vn/) of the Science Activities magazine (under the Ministry of Science and Technology), December / 2007.

Below we will focus on PM10 dust, because other pollutants such as SO2, NO2 and CO have the same developments.

Which month does Hanoi's air get the most polluted?

Figure 1. Monitoring results from 1999 to 2006 of Vietnam Atomic Energy Institute

See Figure 1 above for clarity. Every year, PM10 dust winter is higher than summer, highest in December to January, lowest in July-August. Anticyclonic mode with the northeast monsoon in winter in the North makes the air confined, tends to compress down, dust and pollutants emit difficult to disperse and dilute.

In contrast, in the cyclonic mode in the summer, the ground is heated, the air is easily lifted up, facilitates dispersal and dilution of pollutants more easily. In addition, more rain makes pollutant levels drop sharply, although emissions may not be different between the two seasons.

Which day is the most polluted air in Hanoi?

Figure 2. Results of PM10 monitoring in the dry season, from October 2003 to January 2004 at the automatic monitoring station of KTTV in Lang Biological Garden.PM10 content in micrograms / m ³ .

The triangles on the horizontal axis mark the days when the northeast monsoon spilled over Hanoi (sudden drop in temperature, see the first diagram). A few days ago and then, the lowest level of pollution was due to strong winds, sometimes rain, and the atmosphere in the disputed area between two hot and cold air masses was strongly disturbed.

But then there were the dry days, the mild northeast wind, the beautiful sunny day, the cold night, the complete silence from the night. This kind of smooth weather (less disturbing) is more likely to cause heat-induced heat-induced night radiation.

Heat stress occurs right after sunset, coincides with the peak traffic time, causing pollutants to accumulate near the ground, their content increases until 9-10 pm. So on the days between the next two northeast monsoon winds in the dry season, pollution increases, PM10 content often exceeds the standard of 150g / m ³ (horizontal red line), and high night pollution. more than the day, something few people expect.

According to Figure 2, from October 2003 to January 2004 there were 47 days of heavy pollution, focusing on seven sessions. The two heaviest waves in late October and December 2003 lasted for more than 10 consecutive days.

During this time, all air pollutants were high, in addition to the large, very uncomfortable day and night temperature differences. Elderly and children with respiratory and cardiovascular diseases should be noted.

From January to April 3-4, humid weather due to monsoon air often infiltrates into the North through the Gulf of Tonkin. But another type of heat inversion at a height of several hundred meters, characterized by the vortex regime, called "subsidence inversion," still works, leaving the days of the sky murky because of the Tiny dust absorbs sunlight.

Non-observational documents at meteorological gardens The most complete luminescence we had in 1998 - 1999 showed that there were 43 times of heat exchange due to radiation at night from October 1998 to January 1999. and 37 inversions of heat from January to March 1999.

When is the most polluted day?

Figure 3. The average daily movements of pollutants in May and November in Hanoi according to the observations of the hydrometeorology center.Contaminant content on vertical axis calculated in micrograms / m ³ .

Figure 3 shows the daily evolution of three pollutants averaged over the first two months of summer (May) and early winter (November) in 2003. For NO ₂ and PM10, there are two peaks every day. Pollution reflects peak traffic hours at 8 am and 7 pm. As for SO ₂ , the maximum peak in the morning appears later, at nearly 10 o'clock, when the coal burners are active. The maximum comparison of the morning with the evening in Figure 3, the reader will discover many interesting and useful things.

What may be surprising to many people is that air pollution is usually the lowest at noon, from 12 to 2-3 pm, when the atmosphere is strongly disturbed by the heated ground. From late to late morning is also a time of low pollution.

As a reminder, the above mentioned trends are average trends in May and November. The picture may be more bold, or slightly different when considering each specific day and month.

For example, in the dry season, when there is heat-induced heat radiation at night, pollutants often rise very high after dusk. PM10 at 8-9 pm may be ten times higher at 2-3 pm, then reduce. But the next morning, the pollution level may increase again when the fog appears before sunrise. And then there was the morning traffic rush hour .

Lessons and photos: Pham Duy Hien