Prerequisites for taking into account the influence of air exchange in the design of residential districts in the regulatory documentation

Vdovina Elizaveta Vyacheslavovna Engineer, Siberian Federal University 660041, Russia, Krasnoyarskii krai krai, g. Krasnoyarsk, ul. Prospekt Svobodnyi, 79 doroninalisa21@mail.ru

The problems of air exchange in urban conditions

Social and economic systems are developing rapidly in Russian cities every year, but attention to the ecological system has been highlighted relatively recently. With the advent of statistics of the dirtiest cities in the world, it became clear that industrial cities in Russia annually fall into this list. The process of improving the ecological system, without harming the economic system, takes a long time. It is also not possible to move this or that enterprise to another place. But industrial waste products poison the soil and air every day.

In particular, the waste released into the air is quickly carried by the wind, and in the best case, when these harmful gases quickly leave the city. Unfortunately, in some cities, due to the geographical features and density of urban development, these emissions are delayed and negatively affect the residents of the city. And if we cannot influence geography, as well as weather conditions, then it is more carefully possible for us to think through the planning of further development of the city or the restructuring of some neighborhoods.

In Krasnoyarsk, there are a number of factors that negatively affect the environmental situation. It should be understood that the city is located in the valley of the river, which plays a huge role in the formation of landscapes. In the vicinity of the city there are 8 terraces of different heights and lengths, on which the districts of the city are located ^[1]. Part of the Central and Railway districts are located in the lowlands, Akademgorodok is located on the Sayansky ridge, Sovetsky and Oktyabrsky districts are on a hilly hill. The Sverdlovsk region is located in the foothills of the Eastern Sayan; most of the Kirov and Leninsky districts are located in the lowlands lying between the Yenisei riverbed on the north side and the hills on the south ^[2].

Figure 1 – Map of the location of terraces on the territory of the city of Krasnoyarsk (Source: ^[3])

The first reason is clear, it is the geography of the location of the city, which does not contribute to the ventilation of harmful substances, but only accumulates them in the lowlands of the city. Figure 1 clearly shows that the right bank and part of the left bank are located in a lowland, and they are densely built up, and sleeping areas are located in these lowlands.

Krasnoyarsk is an industrial city in Russia, which consistently ranks among the top 50 cities in the world with the most polluted air. ^[4] In Krasnoyarsk, the concentration of harmful substances in the atmospheric air exceeds the norm by several times and it increases every year. In this city, the "black sky" mode is most often introduced.

For the third quarter of 2021, there are 14 operating plants in the city, including such giants as RUSAL, Krastsvetmet, Krasmash, cement plant. According to the volume of maximum permissible emissions, the largest emissions into the atmosphere are produced by JSC RUSAL Krasnoyarsk. Its total emissions account for 40.0% of citywide industrial emissions into the atmosphere ^[5].

The third is the presence of hydroelectric power plants. Its construction affected the local climate. It was assumed that the length of the ice-free polynya below the Krasnoyarsk HPP would be no more than 30-40 kilometers. In fact, it turned out to be about 300, and now even in 40-degree frosts, the water in the Yenisei does not freeze. As a result, in windless weather at an altitude of 100-150 meters, the city is covered with a cloud of water vapor like a lid ^[4]. 

Krasnoyarsk is also heated with coal by three thermal power plants. Which contributes to a large emission of carbon dioxide. The transfer to more environmentally friendly power plants is not expected in the near future, as it is not economically feasible, having large coal mines nearby.

If we take into account that the city's population is more than a million people, and for every thousand Krasnoyarsk residents there are 300 cars, which is even higher than the Moscow indicator, then it is worth understanding how much carbon monoxide is emitted into the air.

To understand how the air exchange takes place in the city, consider the wind rose.

Krasnoyarsk is characterized by the constancy of the wind regime throughout the year, which is explained by the conditions of orography. At the same time, the direction of the Yenisei Valley coincides with the prevailing wind direction. The width of the Yenisei Valley within the city varies dramatically, which affects the speed of the wind flow and, as a consequence, the intensity of ventilation of the territory. At the outlet of the river from the mountains of the Eastern Sayan, the valley expands significantly, reducing the average wind speeds.

In the repeatability of wind directions and calms by 16 points, it is obvious that during the year the winds of three points prevail: west-southwest; west; west-northwest.

Figure 2 – Wind rose in Krasnoyarsk

(Source: Internet resource - https://weatherarchive.ru /)

In the studied article on the transformation of microclimatic conditions of the urbanized environment, it is indicated that the development of the city has a significant impact on the redistribution of air flows. In a big city, the wind deviates from its natural direction. With closed buildings, it blows along long and straight street highways.

The wind is also influenced by the heat of a large city. Due to the presence of a temperature difference between the central districts of the city and its periphery, a system of cyclonic air currents arises – the warmer air rising up from the central districts of the city is replaced by colder air from the periphery. This influence of the city is manifested mainly in weak winds not exceeding 3 m/s. Sometimes, in cloudless calm weather, small local turbulences caused by thermal differences can form on the streets and even in courtyards. This is an indicator that harmful impurities linger in the residential area.

The distribution of harmful impurities in the atmosphere significantly depends on the nature of the daily and annual course of weak winds. The frequency of weak winds in the city of Krasnoyarsk is significant throughout the year and averages 41-50% according to long-term data ^[6].

When the wind weakens to calm, impurities accumulate, but at this time the rise of superheated emissions into the upper atmosphere increases significantly, where they dissipate. If an inversion is observed under these conditions, then a "ceiling" may form that prevents the rise of emissions. Then the concentration of impurities near the earth increases dramatically. That is, many areas located in the lowlands suffer the most.

Not only citizens suffer from the dust of Krasnoyarsk, but also residents of nearby areas. The wind, as a rule, carries urban dust to the Kuznetsovsky plateau, towards the village of Atamanovo and the city of Zheleznogorsk. The mountains adjacent to the eastern side form a natural barrier here, so all the dust settles mainly in this area. The halo of the dust cloud spreading from the regional center reaches 10,856 km2, while Krasnoyarsk itself occupies only 300 km2 ^[3].

Krasnoyarsk is developing, new buildings are being erected and entire neighborhoods are being built up. In the constructive field of construction, a rapid development has taken place over 30 years, which is noticeable by the increase in the height of buildings, their configuration and volume-planning dimensions. It is known that the wind speed also increases with increasing altitude.

The article by D. Micallef examines how the wind flow is distributed around a simple building, as the study shows is relatively complex (Figure 3). On the sides of the building, including the roof, there will be a separation zone. A vortex will be present. On the leeward side of the building, you can find highly turbulent wake with interesting vortex structures found near the leeward facade of the building. Also, an air dome is formed behind the building, due to a collision with an obstacle, therefore, there is no direct blowing behind it, but only various vortex flows ^[7].

Figure 3 – Air flow distribution

(Source: ^[7])

So, all of the above reflects the modern picture of the city. The environmental situation is deplorable, but they are trying to fix it by modernizing the industry. The energy sector will not undergo significant changes in the next decade, therefore, emissions from thermal power plants and cars will continue to heavily pollute the city's air.

In turn, most of the residential buildings in Krasnoyarsk were built in the last century. It is not advisable to rebuild already built-up neighborhoods. How new high-rise buildings affect air exchange is not fully understood. For a complete picture, it is necessary to consider how the quarters of the sleeping areas of the city of Krasnoyarsk were built up. What normative literature was used for the design of neighborhoods and what decrees and resolutions were introduced to improve the environmental situation of the city. Since the location of houses, their height and the distances between houses have a strong influence on air exchange, the question arises how these parameters were set earlier.

 Identification of periodization

The modern appearance of Krasnoyarsk has developed according to a number of historical events. The task of the study is to understand on what principle sleeping quarters were built up and what regulatory documents contributed to this. Find ways to solve environmental problems in the field of construction in the past.

Krasnoyarsk is one of the oldest cities in Siberia. It was founded in 1628. Krasnoyarsk received the status of a city in 1690. Originally it was a wooden prison, which suffered a great fire in 1773, after which 30 houses remained and all the fortifications were lost.

In 1822, by royal decree, the Yenisei province was created, and Krasnoyarsk became its center. In the status of the capital of the province, the city needed a new perspective plan. The initial version of the plan was prepared by the Yenisei provincial architect Peter Votsky. In fact, he fixed the boundaries that Krasnoyarsk had reached by this time, since the local authorities did not see any prospects for further large growth of the city. Engineer and architect William Geste designed the city plan and pushed the western border of Krasnoyarsk to the foot of Mount Athos, it was almost twice the length of the city at that time. On December 2, 1828, the general plan of Krasnoyarsk was approved by Emperor Nicholas I ^[8].

Figure 4 – Plan of Krasnoyarsk in 1927

(Source: Photo from the collections of the Krasnoyarsk Museum of Local Lore)

It is important to understand that before the general plan of 1828, all the buildings were wooden and were private property. After that, the first stone buildings began to appear. The layout was linear and all further construction was built according to the plan shown in Figure 4.

Further, architecture is closely intertwined with history. And in order to trace the changes in the regulatory literature, the environmental situation and changes in the development of microdistricts, using the example of the city of Krasnoyarsk, we will distinguish three time periods, where each will have its own distinctive features. For example, the degree of detail of normative literature, the characteristic type of typical development, all these factors were closely related to historical events. Periodization is justified by the entry into force of new regulations and regulations affecting them, as well as with the development of ecology.

  In 1917, the Russian Empire ceased to exist. The stage of formation of Soviet architecture begins. It was during this period that resolutions related to the construction industry and the first town-planning norms began to appear. Ecology at that time was a young science that did not have a strong influence. Therefore, the time period from 1917-1940 can be distinguished as a stage in the formation of primary normative literature.

1941-1945 - during the Great Patriotic War, there was stagnation in the urban planning industry. New buildings are not being built, existing buildings are being significantly damaged. During this period, strategically important factories are urgently evacuated in the conditions of military operations. This period will not be further considered.

In the post-war period (1945-1960), the main urban planning tasks are associated with the restoration of cities destroyed by the war. An increase in construction volumes was required for the settlement of the working class. New plans were created for many cities, and in the constructive part there were changes in the process of erecting buildings and increasing the number of storeys of the building to accelerate the pace of settlement. There are new urban planning standards 

 The period of industrialization of construction (1960-1990). Mass resettlement continues, new types of housing of improved quality appear. This period is saturated with urban planning norms, in each of which edits and their modification are made. During this period, there is also a short-term publicity about environmental problems. Changes are being made to the principle of placement of residential buildings.

It is easier to consider each time period on the example of a certain city, in this article the microdistricts of the city of Krasnoyarsk act as the object of research.

Formation of normative documentation on urban planning in the period 1900-1940

            In the Russian Empire there was a Building Charter of the Russian Empire, its last edition dates back to 1900. He was a document in which the provisions of the placement of private property were chaotically described, often even contradictory to each other. The only principle for the placement of buildings was regulation 277 ""On not allowing households to put mansions close to the neighboring border ..." ^[9], which was based on the inconvenience of passages and driveways, and also on the complaint of a neighbor, the structure had to be demolished. This document was not considered when creating the first construction documentation in the USSR, as there was the abolition of private ownership of land and other large immovable property.

            In 1917, according to the plan of the first five-year plan, the planned nature of the socialist economy was established, which created new opportunities for urban planning. Already in the period of the formation of Soviet architecture, social problems of settlement played a decisive role, largely determining the approach of architects to the search for one or another basic planning scheme ^[10].

            The Soviet government had a plan for the industrialization of the country. In many cities there was a clear division between the city and the village, it was necessary to unite them for the integrity of the urban appearance. The former proletarian suburbs did not have well-maintained dwellings, engineering equipment (water supply, sewerage, lighting) and roads, which were so necessary for the creation of residential complexes for workers.

            The primary structural unit — the block — consisted of eight residential buildings, four buildings for children's institutions and a canteen club. From 1920 to 1930. low-rise housing is becoming the most common type of construction for workers not only in towns, but also in cities. The first houses made of three-dimensional elements appear, for which there were no regulatory documents at that time. This contributed to the creation of the first construction regulatory document

In 1930, the Rules and Regulations of "Development of settlements, design and construction of buildings and structures" ^[11] came into force. This regulatory document describes the rules for the development of populated areas.

In this document, according to the factors of air exchange that interest us, it is assigned that the building area should occupy 30% of the quarter ^{[11, p. 20, 26]}. The distances between the blocks are determined and there is no information about the distance between the buildings of the block. The principle of development is a ribbon system of development, with the location of the longitudinal axes of buildings perpendicular to the main driveways and leaving passages and areas for green spaces between buildings ^{[11, p. 13]}. The side of the block should not exceed 400 m. The minimum size of the block is 1.5-2 hectares, with a density of 200-300 people per hectare. A public passage with a width of 8 m should be arranged in the block. The height of the building is 2-4 floors.

A significant problem was also that it was necessary to lay communication systems, therefore, all existing buildings that did not meet these requirements were planned to be demolished. The placement of blocks had to be made taking into account the terrain in order to reduce construction costs.

The construction of new industrial enterprises in the 1930s determined the construction of new large residential areas. As a rule, a road was laid next to the plant, along which residential quarters for workers were formed. The construction of factories led to an increase in the population of cities, therefore, it was necessary to design new areas. The general plan for the development of the city acquired special significance as a document that allows solving current construction tasks without compromising the prospects for the development of the city.

Therefore, on July 26, 1935, Resolution No. 19 "On approval of the regulations on the chief City architect" was approved ^[12], whose duties include guidance on drawing up detailed planning and development projects of the city.

In this period of time, it is impossible to single out any particular type of residential building that was considered typical. Due to the lack of multi–apartment housing options, a large number of competitions aimed at a variety of layouts have been held since 1920. Since 1932, radical changes have been taking place in many areas of architecture and housing construction. The style of constructivism prevails. There was a wide variety of design solutions, which did not accelerate the process of mass development. In this regard, already in 1937, the first modular system was being developed, which makes it possible to make a significant reduction in the type-forming dimensions. By 1940, the People's Commissariat for Construction had created the first nationwide standard projects of low-rise residential buildings. The main requirement for the composition of the quarter was the creation of architectural unity of the buildings along the highway.          

All of the above can be clearly considered on the example of the city of Krasnoyarsk. Until 1930, Krasnoyarsk was built up according to the Gesta plan, mainly on the left bank. As can be seen in Figure 5, the building was linear. With the advent of industrialization, it was decided to locate the Krasmash and Sibtyazhmash plants in the city. It was decided that Krasnoyarsk would place new factories on the right bank, where there is a lot of free space, an abundance of raw materials for construction, favorable wind directions and currents of the Yenisei ^[13].

Among the first residential areas started in the mid-1930s were houses for workers of the machine—building plant on the Moskovsky Tract (now Krasnoyarsk Worker Avenue), the construction of blocks along the future Vavilov Street.

Figure 5 – The first residential quarter of the Stalin era opposite the Sibtyazhmash plant in 1940 (Source: Photo from the collections of the Krasnoyarsk Museum of Local Lore)

Figure 5 shows the stage of construction of the first residential quarter for workers in managerial positions, since they were allocated living space in the first place. The houses are located linearly, parallel to the road along the longitudinal axes, which contradicts the Rules and Regulations ^[11], but meets the requirements of the composition of the quarter to create architectural unity along the main street. The number of floors of the building is 4. But mostly working settlements in the 30s were still dugouts and barracks, where they lived without sewerage, electricity and running water.

With the issue of ecology in this period, everything is very difficult. Firstly, the word "ecology" appeared only at the end of the XIX century, so in the RSFSR in the first half of the XX century it was familiar only to specialists. The USSR developed along the path of industrialization, built a large number of factories that pollute the atmosphere. Scientists predicted the deterioration of the ecological situation, to which party ideologists declared ecology, along with genetics and cybernetics, as bourgeois pseudoscience. Because of this, the number of scientists in this field has decreased ^[14].

Taking into account all the data, it can be concluded that the relationship between ecology and construction is not observed in this period, and the principles of air exchange. The first rules in the regulatory documentation on the placement of residential buildings were issued in 1930, which state at what angle buildings should be placed and indicate that the building density should be a third of the block.  It is worth considering that during this period the number of storeys of buildings does not exceed 4 floors, mainly two-storey buildings. In fact, it can be observed that the placement angle did not comply with the norms and rules, but obeyed the aesthetic appearance relative to the highway. Until 1920, ecology was a young little-known science, and after that it was declared a pseudoscience, since it criticized the path of industrialization.

Development of normative documentation in urban planning in 1945-1960

            The Great Patriotic War suspended all types of construction production. Many buildings were destroyed, so it was necessary to increase the scale of construction. From an urban planning point of view, freedom of creativity was opened in the creation of new master plans of cities. In the pre-war period, there was a question of how to lay communications without affecting existing buildings. After the war, this process did not cause such difficulties.

            In 1946, the fourth five-year plan for the restoration and development of the national economy of the USSR was adopted. It was required in a short time to eliminate the dugouts and barracks in which people lived in the areas of the former occupation and to build new ones, as well as to foresee the possibility of further development of the country's productive forces. It is worth noting that most of the work on the restoration of the country was completed by 1950 ^[9].

            In the same year, the first house-building plants appeared, the final product of which was completed multi-storey residential buildings. The introduction of new industrial methods of housing construction from enlarged elements of industrial production required the restructuring and methodology of standard design. A system of modular coordination of space-planning parameters was developed, which made it possible to consistently unify the space-planning and structural parameters of buildings as an important condition for reducing the nomenclature of building elements and structures, factory-made ^[10].

In 1954, the All-Union Meeting of Architects, Engineers and Builders was convened. The Meeting recognized the need for a rapid transition of all construction to industrial factory construction methods, the progressive capabilities of which have already been proven in practice. At the same time, it was found that the artistic orientation of architecture, the presence of decorative archaic excesses in it, inhibit the development of progressive construction methods.

All of the above events have led to the revision and expansion of the normative construction literature. In 1954, building codes and regulations came into force, which now consist of 4 parts ^[15]. Part II is devoted to the norms of construction design. If in the first period the area of regulation of construction design was described by twenty-one points ^[11], now after carrying out a large number of construction works, the rules and regulations are set out on 400 pages.

We are interested in section B, chapter 1, section No. 3 "Planning and development of residential areas". This section describes in detail the requirements for the building density of the block, depending on the number of storeys of buildings. It is worth noting the inverse proportional relationship, the higher the number of floors of a residential block, the lower the percentage ratio of buildings to the total area of the block. The maximum building density does not exceed 35%, this value is acceptable for 3-storey buildings. The distances between the ends and long sides of residential buildings are determined, according to sanitary and fire requirements. On the long side of the building, the minimum distance between buildings is 12 meters ^{[15, Table 3]}. The minimum fire gap between the ends of the building is 6 meters ^{[15, Table 5]}. All minimum distances between residential and public buildings are also given. 

Point 12 is one of the most important points for this study. It defines the following requirements: "The layout of residential quarters should be carried out taking into account the requirements for ensuring the ventilation of intra-block spaces, the installation of residential premises, the uniform placement of a block or in a group of blocks, all public buildings serving the population, utility rooms, sports grounds, and the like" ^[15]. Therefore, this is the first mention of intra-block air exchange. But this document does not establish specific requirements for ventilation, unlike insolation.

             Unlike the previous period, typical types of residential buildings can be distinguished in the post-war period. The main type of housing (1935-1955) was the following series of houses, presented in Table 1. They were popularly called "stalinki" — a building made of light orange brick or reddish mineral panels, with apartments with a good layout and a high ceiling. Common series: II-01, 1-405, II-03 and II-08 [Appendix 1].

"Stalinka" was quite comfortable housing, but its construction took a lot of time, and because of the large quadrature of apartments, not so many families could be settled. This problem is raised again in Resolution No. 931 "On the development of housing construction in the USSR" of 1957, where they again set goals for increasing the living area until 1960 ^[16].

In Krasnoyarsk, stalinki were placed linearly parallel along the longitudinal axes to the road, thereby creating a single composition of the quarter. The most common series II-01 in 4 floors and 5-storey individual series. Figure 6 shows the construction of the II-01 series. The distances between the buildings in Figure 6 on the end side are 12 m, which meets the requirements of norms and rules ^[15]. Distances along the long side of the building are also observed, more than 2 building heights.

Figure 6 – Residential buildings of series II-01 on Michurina Street 1952

(Source: Photo from the archive of Leonid Sizov, 2GIS)

Later, new serial 5-storey houses for the working class were developed – "Khrushchevki". Appendix 1 in Table 2 presents a series of houses from 1955-1960. This type of housing was built in record time from ready-made reinforced concrete panels. The quality of housing was satisfactory, as well as these buildings were characterized by apartments of small quadrature. But this type of housing allowed to settle a large number of workers in a short time. Common series: K-7, 1-507 and II-35.

From the "Khrushchev" quarters could be built up, or these buildings could be erected on empty places of blocks consisting of stalinas.  This did not cause any problems, since the number of floors of the buildings was the same. But by the end of this period, a new regulatory document is being introduced.

 On February 1, 1959, the rules and norms of "Urban planning and development" CH 41-58 were adopted ^[21]. This document records a radical change in the approach to the organization of the residential zone, and lays the conceptual basis for the entire subsequent development of the regulatory framework of urban planning. In order to improve ventilation, it is declared necessary to abandon perimeter development in favor of a free layout, the location of buildings according to the terrain ^{[21, Article 27]}, the creation of microdistricts, the enlargement of small blocks and the reduction of building density ^{[21, Article 28]}. To improve the quality of the environment and sound insulation from roads, it is required to plant tree plantations. This article was promoted by Resolution No. 555 of 1947 "On measures to improve urban greening" ^[23].

There were ecologists in the USSR after the war, and they made reports on the ecological state of cities, but the figures were unreliable, or rather those that suited the party ^[14]. But the country is aimed at improving the quality of life, the percentage of landscaping has been increased in the quarters, and it is customary to plant poplars in industrial cities. These trees produced a large amount of oxygen and grew rapidly, which was very important for the rapid greening of the city.

So on May 29, 1949, Resolution No. 2196 "On measures to combat atmospheric air pollution and on improving the sanitary and hygienic conditions of populated areas" came into force ^[24]. This resolution has only 1 paragraph, which declares that since 1949 it has been prohibited to erect, reconstruct factories that do not have installations that capture harmful substances (ash, dust).

So, the post-war period is characterized by an increase in the pace and number of residential buildings being erected. With the experience of construction, the requirements for construction are expanding. Building design standards are being created in 4 parts. This document is the first version of the existing joint venture and GOST standards. The first rules for building blocks are established, and by the end of this period, adjustments are made for the placement of buildings and there is a departure from the quarterly development. It is in this period that the first mention of air exchange in urban conditions is noted, but there is no specification, only in CH 41-58 perimeter building is not recommended. Sanitary sections are created relative to the insolation and comfort of living. In the ecological situation, there is an appearance of environmental improvement due to the planting of tree plantations, since it was not part of the party's plans to reduce production rates and install expensive treatment facilities.

Modification of normative documentation in urban planning in 1960-1990

Since 1960, it could be argued that urbanization throughout the Russian state has become a full-fledged and most important form of social development of socialist society.

The USSR has already existed for more than 40 years, during which time the path of industrialization aimed at developed industry began to give a side effect that affects the environment. It was necessary to find a solution to the problem of improving the city. Therefore, the district layout, especially after the XXIII Congress of the CPSU, begins to develop primarily in the territories of new industrial development — the northeast, the east and the Central Asian republics. The estimated time frame for the development of the city's master plan is being increased and the development of forecasts for the development of cities and all types of urban construction is being organized.

In 1969, the Central Committee of the CPSU and the Council of Ministers of the USSR adopted a decision "On measures to improve the quality of housing and civil construction", in which he noted the significant shortcomings of the architecture of mass construction, the dullness and standard architectural appearance of new residential areas. This decision outlined the development and creation of new types of construction and finishing materials that expand the artistic possibilities of industrial construction architecture ^[10].

The improvement of urban planning and compositional skill of architects has found its embodiment in large developed spatial compositions, in contrasting the multifaceted interior spaces of microdistricts.

The quarterly development remains in the past, now the architects face the task of diversity of the development of the microdistrict. Microdistricts were supposed to create a special living environment, which, according to Soviet experts, is intrinsically collectivism.

For the design of residential districts , the architects adhered to the following basic principles:

- variety of layout;

- walking distance to all significant infrastructure facilities;

- placement of the required number of public buildings, according to the population density in the residential area;

- availability of green squares and parks;

- there should be no transit passages through the yard territory in the microdistrict;

- take into account sanitary and fire safety standards when placing buildings ^[25].

The normative literature has undergone a number of modifications, and by this period of time the content and method of presentation is as close as possible to this current construction documentation.

Building codes and rules "Planning and development of populated areas" from 1960 – 1990 was revised three times in 1962, 1975 and 1989. And in each new regulatory document, you can observe changes in the design sections of the residential area.  

In SNiP II-K.2-62, the first structural unit should be a microdistrict ^{[25, p.5.2]}. The main building is five–storey, in places with limited development and at high construction costs – nine-storey ^{[26, item 5.7]}. This normative document determines the density of the housing stock per 1 ha of the microdistrict ^{[26, Table 7.8]}. The gross density for building mainly 5-storey buildings will be 32%, for 9-storey – 42%. Gaps between buildings are declared according to this SNIP and fire protection measures, and are 15-30 m and 44-48 m, respectively. According to paragraph 5.21, the development of microdistricts should be designed using standard projects that meet local climatic and living conditions. The orientation of buildings should be taken into account with respect to the requirements of insolation ^{[26, p.5.24]}.

A distinctive feature of this document from the previous one is an increase in the number of floors and the density of buildings, the absence of any information about the accounting of the blowing of the neighborhood.

Due to scientific and technological progress, the field of knowledge in the construction sector has also expanded. The city has its own climate, and its negative characteristics, superimposed on unfavorable factors of the macroclimate, create especially difficult conditions for humans. In the next edition of the SNIP from 1975, the climatic zone of the city in which the design is carried out is taken into account. 

In SNiP II-60-75** Building codes and Rules "Design standards. Planning and development of cities, towns and rural settlements" when housing construction objects are located, it is required first of all to develop territories free from development ^{[27, p.5.6]}. The number of storeys of residential buildings is now determined on the basis of feasibility studies taking into account architectural and compositional, social, hygienic, demographic requirements and local conditions, but 5-storey buildings are still preferred ^{[27, p.5.4]}. In this SNIP, the definition of the indicator now directly depends on the climatic zone, and also amendments to the seismicity and height of the construction microdistrict are now in effect. The gross density values have been increased, now it will be 53-59% for buildings with mainly 5-storey buildings, 66-76% for 9-storey buildings. Residential density indicators and distances between residential buildings are no longer regulated by this document. Now these indicators should be calculated based on the norms of insolation ^{[27, p.5.19]}. However, the distances for buildings of 2-4 floors are strictly defined.  

In 1989, in SNiP 2.07.01-89* "Urban planning. Planning and construction of urban and rural settlements" ^[28] the concepts of a microdistrict and a residential area are introduced. Distances between residential buildings should now be taken not only on the basis of insolation calculations, but also in accordance with fire protection requirements ^{[28, paragraph 2.12]}. The exact distances are now indicated for buildings with a height of 2-3 floors and separately for buildings with a height of 4 floors. A very important item 9.8 "Protection of the atmosphere from pollution" appears in relation to our study. It is required to place buildings on residential territory on the windward side in relation to industrial enterprises that are sources of atmospheric air pollution, as well as representing an increased fire hazard.

This point is very important, since this is the second mention of air exchange in urban conditions in the regulatory literature.  In this case, only the best location of the building relative to the enterprises is also indicated. But in practice, these instructions were rarely followed.

By 1980, 70 percent of the housing was assembled from ready-made parts. By this time, almost indistinguishable boxes could be found all over the country from the Central Asian steppes to the Arctic Ocean. The five–storey "Khrushchev" buildings were replaced by "Brezhnevki". Initially, eight-nine-storey houses of the series by the mid-70s had grown to 12 and 16 floors. Elevators and garbage chutes appeared in the Brezhnev houses. Heat and noise insulation has been significantly improved. The layout in the "Brezhnevki" has become much more convenient. "Brezhnevki", the construction of which began in 190, are in many ways prototypes of modern standard new buildings. The most common series of this type of housing were II-18/12, 1-464, II-49, and the most common series 114-85. 

Krasnoyarsk in the 1970s was mainly built up with five-storey buildings, and mostly new territories were developed, or new buildings instead of barracks. Therefore, the distances between buildings and the density of residential buildings are observed according to the then current SNiP II-K.2-62. In Figure 7, you can observe the area of the bridge square, where it is clearly visible that the distances and number of floors are observed.

Figure 7 – Construction of the Bridgehead area in 1970

(Source: Photo pastvu.com )

Further development took place already in existing areas, in which among the five-storey buildings "Brezhnevki" were completed, or houses of series 114-85 were built linearly along the main road.

Another series of houses 111-142 ("Leningradki"), common in 1975 – 1989, significantly reduced the shortage of residential buildings. Frame-panel five-storey houses. A garbage chute is designed in the entrances. There is no gasification in these series. Most of the houses in this series can be found in the village "Pervomaisky" and in the residential area "Vetluzhanka". This series of houses was built in all districts both in new territories and in place of 2-storey buildings and barracks. The most common layout of the block is a square consisting of 4 buildings of this series, in the center with a courtyard area. It is worth noting that the distances between buildings have been significantly reduced, and the density of buildings has increased.

Figure 8 – Typical building of a residential district of houses of the 111-142 series

(Source: 2GIS)

Figure 8 shows the square layout of the buildings of the 111-142 series of houses. Minimum permissible fire-fighting distances between houses are observed. Distances between schools, kindergartens and residential buildings are observed. Two houses in a square layout are always connected, and an opening is made between them. According to paragraph 9.8 of SNiP 2.07.01-89*, this angular connection should not be located on the windward side, and for Krasnoyarsk the predominant wind direction is south-west.  Figure 8 shows violations of this requirement.

            It is understandable for what reason so important point 9.8 appeared in the 1989 SNIP. Since since 1960, significant changes for the better have been observed in the field of ecology ^[35].

So in October of that year, the law "On Nature Protection in the RSFSR" was approved ^[34], which entailed a lot of changes in the system of environmental management and control over nature protection. The emergence of the first student Nature Protection Squad at Moscow State University in December, which marked the beginning of the entire Russian environmental movement.

At the second stage (1960-1991), due to the sharp deterioration of the environment and awareness in society of the threat of destruction of the natural balance, there is a gradual formation of the environmental policy of the Soviet state, the main trends of which we will consider further.

Due to the sharp deterioration of the environmental situation in the country, in the 1960s and 1980s a number of laws and regulations were also adopted aimed at preventing environmental pollution ^{[28, pp. 211-225; 7, pp. 317-321]}. At the same time, responsibility for the implementation of the adopted documents was assigned to regional and local authorities, as well as economic ministries and departments, which were the main destroyers and pollutants of the natural environment. Thus, the same officials were often responsible for the process of exploitation of nature and for its protection, and therefore many requirements of environmental legislation were simply not fulfilled, since they significantly slowed down or made it impossible to fulfill production "plans" at all. As a result, the rhetoric of party and government resolutions became tougher over time, and the environmental situation in the country became worse ^[30].

This period accommodates a large number of events, both in the construction industry, the regulatory framework and environmental activities in the country. With regard to air exchange in residential neighborhoods, mentions in SNIPS disappear at the beginning of this period. But thanks to the activities of environmental policy, an item on the protection of the atmosphere from pollution is subsequently added to the regulatory literature, it only regulates the location of buildings. The situation of ventilation is aggravated by an increase in the density of residential buildings and a reduction in the distance between buildings, that is, the height of buildings increases, the distance between houses decreases, the density increases, as can be seen from the example of the requirements of the SNIP are not always met. All these factors lead to stagnation of harmful substances, especially in such an industrial city as Krasnoyarsk.

Information from the current regulatory documentation

When studying the current regulatory literature, there was no single basic set of rules or state standard that would regulate aerodynamics in cities. But at the same time, there is a guide for assessing and regulating the wind regime of residential buildings, on the basis of which it is possible to determine the effectiveness of various architectural and planning solutions for buildings in terms of creating comfortable aeration conditions. Also in this standard, computational methods for assessing and predicting wind conditions in residential buildings at the stage of detailed design are given, available in complexity for use by architects, designers ^[32].

When designing urban space, the assessment and forecasting of the wind regime should be considered as an integral part of the work carried out during the development of the section "Nature protection ...", according to paragraph 1.3. But this guide is intended for use in the development of vacant territories, and not to address issues of regulation of the aeration regime in the conditions of reconstruction, although in these conditions it is partially applicable.

The degree of air pollution significantly depends on the wind speed. According to the research literature, wind directions in built-up areas change on average by about 10-20 °, while wind speeds tend to decrease by an average of 20-30 percent, but low-speed winds tend to increase.

 Data for predicting dangerous wind speed, its direction and parameter P are normalized by RD 52.04.306–92 "Nature protection. Atmosphere. air pollution forecast guide" ^{[33, p.2.1; 3.2; 4.1]}. In Krasnoyarsk, at wind speeds of 0-1 m/s, when horizontal transport is weakened, and convective transport is insufficient to remove impurities, there is an increase in concentrations of pollutants coming from low sources.

According to SP 42.13330.2016 "Urban Planning", the concept of building density is the same as the building coefficient, only the figure is expressed as a percentage. The distances between buildings remained the same, as in SNIP 2.07.01-89* ^[28] This set of rules regulates some point objects of research in paragraphs 6.3, 7.6 ^[31]. Appendix B presents indicators of the density of development of sites of territorial zones, . and it varies from 60-20% ^[31].

The distances between residential buildings should be taken on the basis of calculations of insolation and illumination in accordance with the requirements given in section 14, the illumination standards given in SP 52.13330.2016 ^[35], as well as in accordance with the fire protection requirements given in section 15.

conclusion

Over the last century, mainly in the era of the USSR, there has been the formation of building regulations, from a single document to a set of regulatory and technical documentation. A retrospective analysis made it possible to trace changes in the factors affecting air exchange in the regulatory documentation. 

The study confirms the evidence of the ongoing processes: the height of buildings has increased, while the gross building density has increased, with the same minimum distances between buildings. Most regulations lack information on accounting for air exchange during design, and the existing ones are not informative enough.

            In different periods of time, a set of functional requirements for quarter planning was established. At the same time, the basic requirement remained: a certain number of residential and public buildings (the number of square meters of space) must be erected on a certain area, and they must be accessible on foot. Place green squares and plantings, design driveways in such a way that there is no end-to-end communication. The rest of the layout depended on the architect's imagination.

            Using the example of a comparative analysis of the planning of Krasnoyarsk microdistricts and the design rules described in the norms, noticeable violations in non-compliance with the distances between buildings and incorrect location relative to the windward side were revealed.

            It is revealed that the principles of air exchange are taken into account in the regulations only in the requirements for the placement of the building relative to the windward side, and is not taken into account comprehensively. Only in recent decades, in the rationing system for the design of residential areas, microdistricts, the issues of air mass exchange have been introduced into a set of criteria for the environmental safety of cities.

             Today, modern digital technology capabilities make it possible to make the processes of calculating the air flow in the neighborhood more efficient when using software – this will allow you to create an editable renewable model of the movement of air and harmful substances in the neighborhood. The use of this kind of models will improve the environmental situation of the neighborhood, increase the design productivity.

According to the results of the study, it was concluded that not all previous standards included effective regulations to ensure the necessary air exchange, or they are completely absent. In these standards, factors affecting effective air exchange (height of buildings, distances between buildings and the angle of the buildings) were determined by other requirements, such as sanitary and fire safety standards, insolation requirements.

Application

Table 1 – Typical series of buildings from 1935-1955

Table 2 - Typical series of buildings 1955-1960-ies

Table 3 – Changes in the value of building parameters

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