Watching the foggy weather leads to your own thinking composition.

The most interesting thing recently is the "smog" weather. This winter, a super smog swept through most parts of China. 104 cities were poisoned and "fallen", and the average haze days were the highest in 52 years; Many cities are caught in a haze.

Jinhua just experienced a dusty weekend some time ago. On the 6th and 7th of this month, the Municipal Meteorological Observatory issued an orange warning signal twice, which is the first time in our city. On the 7th, Jinhua's PM2.5 index was as high as 5 10, exceeding 500 μ g/m3, that is, "off the chart", and the average index reached 482 that day, ranking first in the province.

The occurrence of such a serious haze is not the fault of a city, but caused by a large-scale regional haze weather in the country. In recent years, the average number of haze days in China has increased significantly, especially in the central and eastern regions where industrial development and urban construction are more rapid. In cities affected by smog, the visibility in some areas is less than 100 meters, which leads to the grounding of local flights, the closure of roads, and the obvious increase of patients with respiratory diseases, which has brought serious influence and harm to our production and life and physical and mental health.

First of all, the concept of smog

Fog is an aerosol system composed of a large number of tiny water droplets or ice crystals suspended in the air near the ground, and it is the product of condensation (or sublimation) of water vapor in the air near the ground. Haze, also known as haze, is a collection of a large number of tiny dust particles, smoke particles or salt particles suspended in the atmosphere. Haze makes the air turbid, and the horizontal visibility decreases below 10km. According to the monitoring results of smog weather in key cities by China National Environmental Monitoring Center, the particulate matter that constitutes smog is extremely small, and particulate matter PM 10, especially PM2.5, is the most important component of smog. PM2.5 refers to particulate matter with a diameter less than or equal to 2.5 microns in the atmosphere, which mainly comes from industrial waste gas, coal burning, automobile exhaust, dust and volatile organic compounds. Fog itself is not a pollutant, but the atmospheric environment that produces fog is in a relatively stable state, and pollutants in the air are not easy to spread outward, resulting in agglomeration effect. Under the conditions of low air pressure and low wind speed, water vapor in the lower air combines with haze to form a mixture of fog and haze.

Second, the planning ideas of smog prevention and control

Haze is the product of excessive emission of industrial waste gas and motor vehicle exhaust gas under specific meteorological environment conditions. The key to solving smog is to change the mode of economic development, implement energy conservation and emission reduction, and use pollution-free clean energy. At the same time, the occurrence of large-scale urban smog is related to the unreasonable urban planning and layout, which is a test of the foresight, scientificity, effectiveness and sustainability of urban development. Urban smog urges us to reflect on traditional urban planning and put forward new requirements for future planning.

In view of how to prevent and control smog in Jinhua urban planning, it is still necessary to make targeted research on urban structure, spatial form and layout of high-rise buildings in combination with its own geographical environment and climate characteristics, and put forward reasonable suggestions for government decision-making and urban planning and construction.

(a), reasonable planning of urban structure, reserved control of urban air duct.

Urban ventilation corridor, also known as urban air duct, is to build an ecological green corridor in the city, and open vents in some areas of the city to let the suburban wind blow to the main city, increase the air mobility of the city, blow out atmospheric pollutants, alleviate the smog in the city to a certain extent, improve the microclimate environment and alleviate the "heat island effect" in summer. In a sense, "urban ventilation corridor" is more of a transformation of urban structure.

The construction of large-scale "urban ventilation corridor" can start from three aspects:

The first is to build a green corridor. In the planning and layout, ventilation corridors are set up according to the dominant wind direction of the city, and urban air ducts are set up from the outer suburbs and urban areas. Planning a certain width of belt-shaped green space along urban expressways, highways, railways and rivers, strictly controlling their construction behavior, and forming green air corridors, road air corridors and river air corridors. For example, the construction of urban greenway network in urban areas and the construction of green corridors on the six banks of the Three Rivers have well constructed urban ventilation green corridors.

The second is to build a forest belt around the city called the "green necklace" of the city. Under the condition of constant pollutants, if urban ventilation corridors are built, the diffusion speed of pollutants can be increased. The forest belt around the city is a 360-degree green corridor all year round, and urban air ducts can be formed in any wind direction. Jinhua is a special regional basin with low annual average wind speed. However, with the increasing number of high-rise buildings in cities, air flow and urban air ducts are blocked, which seriously affects urban ventilation and heat dissipation. The overall planning of Jinhua has reserved a certain width of forest belt around the third ring road of the city. However, in the process of detailed urban construction, some places are not completely controlled as required. On the contrary, the high-rise buildings around the First Ring Road and the Second Ring Road surround the main urban area like wooden barrels, which makes it difficult for pollutants in the main urban area to spread and further aggravates urban air pollution.

Third, strictly control the urban tuyere and use six green wedges to form the urban "cross flow". Use natural conditions such as mountain forest land, river valleys and waterways. Through a series of constructions, an open space and an urban "air outlet" are formed by adopting the planning means of building height limit. At present, according to the requirements of the overall urban planning, most of the ecological ventilation corridors in the main urban area of Jinhua have been basically formed and are playing a role, which can ensure the cold air from the suburbs to blow in and replace the hot air in the main urban area. At the same time, the strong demand for land in urban development still leads to the phenomenon that the six green wedges are gradually swallowed up, which deserves our great attention.

The composite construction of the three will produce superimposed benefits, and its overall ecological benefits are stronger than the single ecological benefits. Domestic cities, such as Hangzhou, Wuhan and Shanghai, have carried out relevant research and construction of "urban air duct", while foreign countries, such as Munich, Germany and London, England, have considered the problem of urban air duct in urban planning.

Relevant research and experience show that the construction of "urban air duct" is not designed temporarily, but planned in advance and reserved space. There is no need for demolition and construction, but it can be consciously and gradually completed in combination with the transformation of the old city, the development of the new district, the examination and approval of specific projects, and the construction of our park and ecological belt.

(2) Effectively organize urban space and build urban air ducts.

To build urban ventilation corridors in cities with high-intensity development, on the one hand, we should build green corridors, on the other hand, we should consciously consider the characteristics of climate and environment, such as the direction of roads and the layout of buildings, and consider the dominant wind direction of the city to leave a passage for the wind.

In recent years, the number of high-rise buildings in Jinhua has advanced by leaps and bounds, and the layout is disorderly, which hinders the formation of air ducts. The dominant wind direction in Jinhua is the northeast wind, which requires east-west roads to organize the air duct, and it is best to run through the city. Otherwise, when the wind reaches a certain place and is blocked by buildings, it will "climb over" again, delaying the speed of haze removal and heat dissipation. For example, the splendid Jinhua in Jiangbei is densely lined with a row of tall buildings along the west side of Huixi Park. The cool northeast wind in summer may blow in directly. After crossing the Yiwu River, you can also carry some cool and humid river winds and blow them all the way to the old city along river banks, parks, roads and relatively low buildings. However, with the construction of resplendent high-rise residential buildings on Huixi Street, it just blocked the route where the wind blows from east to west, resulting in a sharp drop in wind speed and aggravation.

In different functional areas of the city, with the different land value and development intensity, the density and location of high-rise buildings are also different. For some urban functional areas that may affect the urban air duct, it is necessary to control and analyze the urban high-rise buildings, especially the high-rise buildings above 100 meters have great influence on the urban microclimate. Therefore, in view of the geographical environment and climate characteristics of the city, it is necessary to carry out research on the height control of urban space in important air ducts and their surrounding areas, such as the study on the location of high-rise buildings along the six banks of the Sanjiang landscape belt, which can not only reserve space for a rainy day, but also control and shape the urban skyline. For example, in 2005, the planning department of Wuhan and Huazhong University of Science and Technology jointly conducted a study on the relationship between urban architectural planning and climate. This study prospectively considers the relationship between urban development and urban climate, which has a good guiding role in solving urban heat island effect and smog from the spatial form.

(3) Considering the relationship between the layout of land buildings and the wind direction, it conforms to the urban passage.

"In the process of urban planning and construction, consciously creating a' wind corridor' can alleviate the occurrence of haze weather and reduce the generation of heat island effect." Xu said.

To build a "ventilation corridor", it is necessary to control the height and number of high-rise buildings, leave a "big gap" in places with many high-rise buildings, and let the city have an "air outlet" like people. Air ducts are reserved to allow the wind to carry pollutants out of the city smoothly.

At the level of plot construction, there is a lack of consideration on the influence of architectural layout on urban microclimate. When a tall building is built, there is no scientific meteorological demonstration, and there is no relevant analysis on whether the height and orientation of the building block the formation of urban air ducts, which makes it difficult for the urban atmosphere to operate in a virtuous cycle, leading to the city becoming a castle with poor ventilation, where the wind can't enter and the smog can't get out, and it becomes a suffocating pollution "siege".

As the dominant wind direction in Jinhua is northeast wind, the best orientation of building layout is about 15 degrees from south to west. If the influence of climate on buildings is considered, the layout of buildings conducive to urban ventilation should have a certain angle with urban streets. However, in plot construction, if high-rise buildings are arranged in the north-south direction, the urban air duct is easy to be blocked. Therefore, it is urgent to study the relationship between urban high-rise building layout and urban climate, reserve the spatial position of high-rise buildings in different plots, and study the influence of different land-use building layout forms on urban air ducts. For example, in the layout form of residential buildings, staggered layout is better than determinant; Point-strip combination is better than single plane layout; Semi-closed surface wind direction is also conducive to the formation of a good ventilation environment.

In the next step, it is suggested to do the following work around the urban structure, spatial form and the layout of urban high-rise buildings:

1, learn from the successful experience of other cities, study the relationship between urban planning and climate as soon as possible, and put forward measures and countermeasures to improve urban microclimate environment from the perspective of urban planning;

2. Start the implementation evaluation of the overall urban planning as soon as possible, correct the problems existing in the process of urban development in time, and make the urban construction more scientific, reasonable and orderly;

3, to carry out the revision of the special planning of urban green space system and the preparation of green line planning, clarify the control scope of all kinds of green lines, and strictly implement them in accordance with the Measures for the Administration of Urban Green Line;

4. According to the special planning of urban green space system, speed up the construction of urban parks, urban green wedges and forest belts around the city, and build an ecological green space system with green belts on the six banks of Sanjiang River as the skeleton, urban green wedges as the tuyere and forest belts around the city as the 360 ventilation corridor.