The effects of industrial technology on the natural environment

There are two types of impacts of human activities on the climate: one is the unconscious impact, that is, the side effects of human activities on the climate; the other is the conscious impact of taking certain measures for a certain purpose. Changing climate conditions. At this stage, the first type of influence dominates, and this influence is most significant in the following three aspects, namely: (1) greenhouse gases and various pollutants emitted into the atmosphere during industrial and agricultural production, changing the chemistry of the atmosphere; Composition; ② Changing the nature of the underlying surface during agricultural and animal husbandry development and other activities, such as destruction of forest and grassland vegetation, marine oil pollution, etc.; ③ Urban climate effects in cities. In the 200 years since the world's industrial revolution, with the rapid increase in population, the development of science and technology, and the rapid expansion of production scale, the adverse impact of human activities on the climate has become increasingly greater. Therefore, it is necessary to strengthen research efforts and take measures to consciously plan and control various human activities that affect the environment and climate, so as to develop them in a direction conducive to improving climate conditions.

(1) Changing the chemical composition of the atmosphere and climate effects

Industrial and agricultural production discharges a large amount of waste gas, dust and other pollutants into the atmosphere, mainly carbon dioxide (CO2), methane (CH4) ), nitrogen monoxide (N2O) and chlorofluorocarbon compounds (CFCS), etc. According to conclusive observational facts, the contents of these gases in the atmosphere have increased dramatically in recent decades, and stratospheric ozone O3. The total amount dropped significantly. As mentioned before, these gases have an obvious greenhouse effect and have two strong absorption bands at wavelengths of 9500 nanometers (μm) and 12500-17000μm, which are the absorption bands of O3 and CO2. In particular, the absorption band of CO2 absorbs approximately 70-90% of infrared long-wave radiation. The outward long-wave radiation of the earth-atmosphere system is mainly concentrated in the wavelength range of 7000-13000 μm. This band is called the atmospheric window. The above-mentioned CH4, N2O, CFCS and other gases each have their own absorption bands within this atmospheric window. The increase in the concentration of these greenhouse gases in the atmosphere will inevitably play an important role in climate change.

The concentration of CO2 in the atmosphere was roughly stable at about (280±10)×10-3ml/L for a long time before industrialization, but it has increased rapidly in recent decades. By 1990, it had It increased to 345×10-3ml/L. After the 1990s, the growth rate was rapid. Figure 8.14 (figure omitted) shows the year-by-year changes in measured values ??at Mauna Loa Station in Hawaii, USA, from 1959 to 1993. The rapid increase in CO2 concentration in the atmosphere is mainly caused by the massive burning of fossil fuels and massive deforestation. According to research, part of the CO2 emitted into the atmosphere (about 50%) is absorbed by the ocean, and another part is absorbed by the forest and turned into solid organisms, which are stored in nature. However, due to the current destruction of a large number of forests, the forest has not only been reduced It absorbs CO2 from the atmosphere, and due to the burning and decay of destroyed forests, a large amount of CO2 is emitted into the atmosphere. At present, there are many different estimates of the future increase in CO2. For example, based on the current CO2 emission level, the concentration of CO2 in the atmosphere in 2025 will be 4.25×10-3mL/L, which is 1.55 times that before industrialization.

Methane (CH4 biogas) is another important greenhouse gas. It is emitted into the atmosphere mainly from the burning of rice fields, ruminants, swamps and living organisms. From 200 years ago to 110,000 years ago, the CH4 content was stable at 0.75-0.80×10-3mL/L. It has increased rapidly in recent years. The CH4 content had increased to 1.25×10-3mL/L in 1950 and 1.72×10-3mL/L in 1990. Dlugokencky et al., based on the observation records of 23 fixed-point land stations around the world and 14 ship observation stations at different latitudes in the Pacific, estimated the global annual changes in CH4 mixing ratio (M) in the atmosphere in the past 10 years as shown in Figure 8·15 (Fig. (omitted) as shown. Based on the current growth rate, the CH4 content in the atmosphere will reach 2.0×10-3mL/L in 2000 AD, and will reach 2.34 to 2.50×10-3mL/L in 2030 and 2050 respectively.

The emission of nitrous oxide (N2O) into the atmosphere is related to the increase in farmland area and the application of nitrogen fertilizers. Supersonic flight in the stratosphere can also produce N2O. The N2O content in the atmosphere before industrialization was approximately 2.85×10-3mL/L. It increased to 3.05×10-3mL/L and 3.10×10-3mL/L in 1985 and 1990 respectively. Considering future emissions, it is estimated that the N2O content in the atmosphere may increase to between 3.50×10-3-4.50×10-3mL/L by 2030. In addition to causing global warming, N2O can also cause odor pollution in the stratosphere through photochemical effects. Oxygen O3 dissociates and destroys the ozone layer.

Chlorofluorocarbons (CFCS) are the main raw materials in the refrigeration industry (such as refrigerators), aerosols and blowing agents. Certain compounds in this family, such as Freon 11 (CCl2F, CFC11) and Freon 12 (CCl2F2, CFC12), are greenhouse gases with strong warming effects. In recent years, it has also been considered to be the main factor in destroying stratospheric ozone, so restricting the production of CFC11 and CFC12 has become a prominent issue internationally.

Before the development of the refrigeration industry, there was no such gas component in the atmosphere. Industrial emissions of CFC11 began in 1945 and CFC12 existed in 1935. By 1980, the CFC11 content in the lower troposphere was approximately 168×10-3mL/L and CFC12 was 285×10-3mL/L. By 1990, it had increased to 280×10-3mL/L and 484×10-3mL/L respectively. , its growth is very rapid. Figure 8.16 (figure omitted) shows the change situation of CFC12 in recent decades. The future changes in its content depend on future restrictions.

Based on specialized observations and calculations, the annual increase in concentration of major greenhouse gases in the atmosphere and their decay time in the atmosphere are shown in Table 8·7 (figure omitted). It can be seen that except for CO2, the contents of other greenhouse gases in the atmosphere are very small, so they are called trace gases. However, their warming effect is extremely strong, and their annual increment is large. They decay in the atmosphere for a long time, and their impact is huge.

Ozone (O3) is also a greenhouse gas. It is produced under the influence of natural factors (generated by the photochemical action of ultraviolet radiation on oxygen molecules in the upper atmosphere in solar radiation), but is destroyed by gases emitted by human activities. , such as chlorofluorocarbon compounds, alkyl halide compounds, N2O, CH4, and CO can destroy ozone. Among them, CFC11 and CFC12 play the main role, followed by N2O. Figure 8.17 (figure omitted) shows the interannual variation ratio of the zonal mean total ozone anomalies in each climate zone (196-1985. It can be seen from the figure that since the early 1980s, the amount of ozone has decreased sharply, with the Antarctic For example, the lowest value reaches -15%, and it is above -5% in the Arctic. Globally, the oscillation should be between ±2% under normal circumstances. According to actual measurements in 1987, it reached above -4% this year. The total amount of ozone between N-60°S has decreased from an average of more than 300 ppson units in 1978 to less than 290 units in 1987, which is a decrease of 3-4% in terms of vertical changes at an altitude of 15-20km. The largest decrease occurred, with a slight increase in the lower troposphere. The most prominent decrease in ozone was in the Antarctic, forming a small area near the center of the Antarctic, called the "Antarctic Ozone Hole". From 1979 to 1987, the minimum value of the ozone minimum center dropped from 270 units to 150 units. Units, the area of ??less than 240 units is constantly expanding, indicating that the Antarctic ozone hole is continuously strengthening and expanding. Although the total amount of O3 rebounded in 1988, the Antarctic ozone hole expanded again on October 4, 1994. A research report published by the World Meteorological Organization shows that ozone over three-quarters of Antarctica's land and nearby seas has decreased by more than 65% compared with ten years ago. However, there is data showing that ozone in the troposphere has increased slightly. p>

Increases in greenhouse gases in the atmosphere will cause climate warming and sea level rise. According to a combination of the most reliable observations available, global temperatures have increased by 0.6-0.9°C in the 100 years from 1885 to 1985. . Figure 8.10 (figure omitted) points out the actual temperature changes from 1860 to 1985 (for the difference in global annual average temperature in 1985), indicating that the global warming trend is also around 0.8°C after 1985. Surface temperatures continue to increase, and most scholars believe it is caused by greenhouse gas emissions. The figure lists the warming effects of greenhouse gas emissions in three different situations. Calculations from climate models also show that this warming is polar. Larger than the equator, winter is larger than summer.

As global temperatures rise, seawater temperatures also increase, which will expand seawater and cause sea levels to rise. Coupled with the intense warming in the polar regions, when Doubling the concentration of CO2 in the atmosphere will cause polar ice to melt and the ice boundary to shrink toward the poles. The amount of melted water will cause sea levels to rise. Actual observation data proves that from 1880 to 1980, global sea levels have risen over the past century. 10-12cm. It is calculated that if greenhouse gas emissions are controlled within the 1985 emission standards, the global sea level will rise at a rate of 5.5cm/10a. By 2030, the sea level will increase by 20cm compared with 1985 and by 2050. 34cm. If emissions are not controlled, sea levels will rise 60cm by 2030 and 150cm by 2050.

According to climate change, the increase in greenhouse gases will have a certain impact on precipitation and global ecosystems. Model calculations show that when the CO2 content in the atmosphere doubles, globally, the annual total precipitation will increase by 7-11%, but the changes will be different at each latitude. Generally speaking, precipitation has increased in high latitudes due to warming, mid-latitudes have become arid due to the northward movement of the subtropical arid zone after warming, and precipitation has increased in the subtropics. Convection has strengthened in low latitudes due to warming, so precipitation has increased. .

In terms of global ecosystems, warming due to human activities will cause parts of the frozen tundra at high latitudes to thaw, and the northern limits of forests will develop further poleward. It will become dry in the mid-latitudes, and some forests and biomes that prefer moisture and warmth will gradually be replaced by biomes currently heard in the subtropics. According to predictions, after CO2 doubles, global deserts will expand by 3% and forest areas will decrease by 11%. , the grassland expanded by 11%, which is caused by the tendency of dry land in mid-latitudes.

The destruction of the ozone layer in greenhouse gases has a great impact on the environment and human health.

The decrease in ozone increases the amount of ultraviolet radiation in the solar radiation that reaches the ground. If the total amount of ozone in the atmosphere is reduced by 1%, the ultraviolet radiation reaching the ground will increase by 2%. This ultraviolet radiation will destroy ribonucleic acid (DNA) to change genetic information and destroy proteins, and can kill single-cell marine plankton within 10m water depth. organisms, reduce fishery yields, and destroy forests, reduce crop yields and quality, weaken human immunity, damage eyes, and increase skin cancer and other diseases.

In addition, there are large amounts of sulfide, nitrogen and man-made dust in the gases emitted by human activities, which can cause atmospheric pollution and form "acid rain" under certain conditions, which can cause forests, There was severe damage to fish, crops and buildings. The rapid increase of fine dust in the atmosphere will weaken the insolation and affect the temperature, cloud cover (there are hygroscopic nuclei in the dust) and precipitation.

(2) Changes in the nature of the underlying surface and climate effects

Human activities change the natural properties of the underlying surface in many ways. At present, the most prominent ones are the destruction of forests, slopes, and drought. vegetation and marine oil pollution.

Forest is a special underlying surface. In addition to affecting the CO2 content in the atmosphere, it can also form a unique forest climate and affect the climate conditions of a large area nearby. The forest canopy can absorb a large amount of incident solar radiation to promote photosynthesis and transpiration, so that its own temperature does not increase much. Due to the obstruction of the forest canopy during the day, not much solar radiation penetrates into the surface of the forest, so the temperature will not rise sharply. At night, due to the protection of the forest canopy, the effective radiation is not strong, so the temperature is not easy to drop. Therefore, the daily (annual) temperature range in the forest is smaller than that in the exposed areas outside the forest, and the continental nature of the temperature is significantly weakened.

The forest canopy can intercept precipitation, and the loose humus layer and litter layer under the forest can store water and reduce surface runoff after rainfall. Therefore, the forest can be called a "green reservoir." Rainwater slowly penetrates into the soil, increasing the soil moisture and increasing the water available for evaporation. Coupled with the transpiration of the forest, the absolute humidity and relative humidity in the forest are greater than those in the bare land outside the forest.

Forests can increase precipitation. When the airflow passes through the forest canopy, it is blocked and rubbed by the forest, forcing the airflow to rise, leading to intensified turbulence. In addition, the air humidity in the forest area is high and condensation occurs. Due to its low altitude, forest areas have more chances of precipitation than open areas, and the amount of rainfall is also greater. According to actual measurement data, the air humidity in forest areas can be 15-25% higher than that in non-forest areas, and the annual precipitation can increase by 6-10%.

The forest has the effect of reducing wind speed. When the wind blows towards the forest, the wind speed will change on the windward side of the forest, about 100m away from the forest. When passing through the forest, the wind speed quickly decreases. If the wind carries sediment, the quicksand will sink and gradually become fixed. After passing through the forest, the wind speed still has a reducing effect within a certain distance on the leeward side of the forest. In arid areas, forests can reduce the attack of drought winds and prevent wind and sand fixation. In coastal windy areas, forests can defend against sea breezes and protect farmland. The secretions from forest roots can promote the growth of microorganisms and improve soil structure. The forest-covered area has a humid climate, good soil and water conservation, and a virtuous cycle of ecological balance, which can be called a "green ocean."

According to research, the world's forests once accounted for 2/3 of the earth's land area in history. However, with the increase of population, the development of agriculture, animal husbandry and industry, the construction of cities and roads, and the destruction of war, , the forest area gradually decreased. By the 19th century, the global forest area dropped to 46%, and at the beginning of the 20th century, it dropped to 37%. The current global forest coverage area averages about 22%. Our country also had dense forest coverage in ancient times. Later, due to population proliferation, farmland expansion and frequent wars during the Ming and Qing dynasties, the national forest coverage rate dropped to 8.6% by 1949. Since the founding of the People's Republic of China, the party and government have organized large-scale afforestation, and the area of ??artificial forests has reached 460 million acres. However, due to a weak foundation, deforestation is quite serious. The current forest coverage area is only 12%, ranking 116th among 160 countries in the world.

Due to the destruction of large areas of forest, the climate has become drier, sandstorms have intensified, soil erosion has worsened, and the climate has worsened. On the contrary, after liberation, our country built various types of protective forests, such as the northeastern and western protective forests, the eastern Henan protective forests, the northwest sand-proof forests, the western Hebei protective forests, the Shandong coastal protective forests, etc., which have played a significant role in transforming nature and changing climate conditions.

In arid and semi-arid areas, grasses and shrubs with strong drought tolerance originally grew. They can survive in arid areas and protect the soil there. However, due to the increase in population, there has been an increase in immigrants in arid and semi-arid areas. They have expanded agriculture and animal husbandry there, and dug and collected xerophytes for fuel (especially plants on slopes), causing natural vegetation such as local grasslands and shrubs to be affected. Much damage. Rainwater on slopes gathers rapidly, flows quickly, and has a strong scouring force on the soil. After losing the protection and blocking of natural vegetation, it will cause serious water and soil erosion. Once a drought period arrives on flat land, farmland crops cannot grow, and the loosened land after reclamation is not protected by vegetation and is easily susceptible to wind erosion. As a result, the fertile surface soil is blown away, while the sand remains, resulting in desertification. A similar situation exists in the animal husbandry industry. The animal husbandry exceeds the load capacity of the pasture. In drought years, the pasture is sparse and the land surface is trampled and damaged by livestock. Severe wind erosion also occurs, causing desertification.

On desertified land, the climate is getting worse. The specific manifestations are: increased runoff after rain, intensified soil erosion, reduced moisture, drying out the local soil and atmosphere, increasing surface reflectivity, destroying the original heat balance, and decreasing precipitation. The climate will become more continental, the surface fertility will decrease, wind and sand disasters will increase significantly, and the climate will become drier, which in turn will be less conducive to the growth of plants.

According to estimates by the United Nations Environment Program, the world currently loses 60,000 km2 of land due to desertification every year, and an additional 210,000 km2 of land has declined in fertility and has no economic value in agriculture and animal husbandry. Word. Desertification also threatens our country. The desertified land formed in northern my country during the historical period is 120,000 km2. In recent decades, the desertification area has increased year by year. Therefore, we must consciously take active measures to protect local natural vegetation and carry out large-scale irrigation. Carry out artificial afforestation and plant drought-tolerant vegetation that can prevent sand and solidify soil according to local conditions to improve climate conditions and prevent further deterioration of the climate.

Ocean oil pollution is another important aspect of today's human activities that change the nature of the underlying surface. It is estimated that more than 1 billion tons of oil are transported to consumption sites by sea every year. Due to improper transportation or tanker crashes, more than 1 million tons of oil flow into the ocean every year. In addition, waste oil generated during industrial processes is discharged into the ocean. Some people estimate that the amount of oil poured into the ocean every year reaches 2-10 million tons.

Part of the waste oil poured into the sea forms an oil film that floats on the sea surface, inhibiting the evaporation of seawater and drying the sea air. At the same time, it reduces the transfer of latent heat on the sea surface, causing the diurnal and annual changes in seawater temperature to increase, causing the ocean to lose its role in regulating temperature, resulting in a "marine desertification effect." The impact of the waste oil film on relatively closed sea surfaces, such as the Mediterranean Sea, the Baltic Sea and the Sea of ??Japan, is more significant than that in the vast Pacific and Atlantic Oceans.

In addition, for the needs of production and transportation, humans have filled lakes and built land, dug canals and built large reservoirs, etc., which have changed the properties of the underlying surface and have a significant impact on the climate. For example, after my country's Xin'an River Reservoir was built in 1960, the nearby Chun'an County had cooler summers and warmer winters than before. The annual temperature range became smaller, the first frost was delayed, the final frost was advanced, and the frost-free period was extended by an average of about 20 days.

(3) Emissions of anthropogenic heat and water vapor

With the development of industry, transportation and urbanization, the world’s energy consumption has increased rapidly. In 1970 alone, the world’s energy consumption The energy is equivalent to burning 7.5 billion tons of coal and releasing 25×10-10J of heat. Among them, a large amount of waste heat is emitted in industrial production and motor vehicle transportation. Residential stoves and air conditioners, as well as the metabolism of humans and animals, also release a certain amount of heat. These "artificial heat" directly warm the atmosphere like a furnace. At present, if the anthropogenic heat is averaged over the entire continent, it is equivalent to releasing 0.05W of heat per square meter of land. Numerically speaking, it is negligible compared with the average net radiant heat obtained by the entire earth from the sun. However, since the release of anthropogenic heat is concentrated in certain large cities with dense population and developed industry and commerce, its local warming effect is Quite significant. As shown in Table 8.8, in high-latitude cities such as Fairbanks and Moscow, the annual average anthropogenic heat (QF) emissions are greater than the net solar radiation; in mid-latitude cities such as Montreal and Manhattan, due to per capita use It has large energy, and its annual average anthropogenic heat QF emissions are also greater than Rg. Especially in Montreal, air-conditioning and heating consume a lot of energy in winter, and the man-made heat is equivalent to more than 11 times the net solar radiation. But for places like Hong Kong in the tropics and Singapore in the equatorial zone, their anthropogenic heat emissions are negligible compared to the net solar radiation.

When burning a large amount of fossil fuels (natural gas, gasoline, fuel oil, coal, etc.), in addition to waste heat emissions, a certain amount of "artificial water vapor" is also released into the air. According to the American Metropolitan Meteorological Experiment ( METROMEX), the amount of man-made water vapor produced by combustion in St. Louis City is 10.8×108g/h, while the natural evapotranspiration from the local ground in summer is 6.7×1011g/h. Obviously, the amount of anthropogenic water vapor is much smaller than the amount of natural evapotranspiration, but it has a certain effect on the increase of local low cloud cover.

It is estimated that the current global energy consumption is increasing by about 5.5% per year. If this rate continues to increase, by the year 2000, the world's energy consumption will increase five times compared to 1970, that is, the annual energy consumption will be 37.5 billion tons of coal. The man-made heat and water vapor emitted by it are mainly concentrated in cities, and their impact on urban climate will increasingly show its importance.

*Meet Zhou Shuzhen and Shu Jiong. Urban climatology. Beijing: Meteorological Press. 1997; 197

In addition, the exhaust gas emitted by jet aircraft flying at high altitudes is mixed with CO2 and a large amount of water vapor. According to research, the water vapor in the stratosphere (50hPa altitude) has increased significantly in recent years. For example, the water vapor content was 2×10-3ml/L in 1964, but rose to 3×10-3mL/L in 1970. This is related to the fact that a large number of jet aircraft often fly at this altitude. The thermal effect of water vapor is similar to that of CO2, and it has a greenhouse effect on the earth's surface. Some people have calculated that if the amount of water vapor in the stratosphere increases five times, the surface temperature can rise by 2°C, while the stratospheric temperature will drop by 10°C.

The increase in high-altitude water vapor will also lead to an increase in high-altitude cirrus clouds. It is estimated that the amount of cirrus clouds has increased by 5-10% on the North American-Atlantic-Europe route where most jets fly. Clouds have a great influence on solar radiation and infrared radiation of the earth-atmosphere system, and they play an important role in climate formation and change.

(4) Urban climate

Cities are the centers of human activities. In cities, where the population is dense, the underlying surface changes the most. Frequent industry, commerce, and transportation consume the most energy, and a large amount of greenhouse gases, "artificial heat," "artificial water vapor," fine dust, and pollutants are emitted into the atmosphere. Therefore, the impact of human activities on climate is most prominent in cities. Urban climate is a special local climate formed under the influence of human activities after urbanization on the regional climate background. In the early 1980s, American scholar Landsbaugh summarized the comparison of various climate elements between cities and suburbs as shown in Table 8.9

From a large number of observational facts, the characteristics of urban climate can be summarized as urban " The five-island effect (turbidity island, heat island, dry island, wet island, rain island) and wind speed decrease and change.

See H.E. Landsberg, The Urban Climate.Academic Press.1981.

(1) Urban turbidity island effect

The urban turbidity island effect mainly has four aspects performance. First of all, there are more pollutants in the urban atmosphere than in suburban areas. As far as condensation nuclei are concerned, the average condensation nuclei content in the atmosphere over the ocean is 940 particles/cm3, and the absolute maximum value is 39,800 particles/cm3; while in the air of big cities The average is 147,000 grains/cm3, which is 156 times that on the ocean. The absolute maximum is 400,000 grains/cm3, which is more than 100 times higher than the absolute maximum on the ocean. Taking Shanghai as an example again, according to monitoring results in the past five years (1986-1990), the average concentrations of SO2 and NO2 gas pollutants in the atmosphere in urban areas are 8.7 times and 2.4 times higher respectively than in suburban counties.

Secondly, due to the large number of condensation nuclei in the urban atmosphere and the relatively strong low-altitude thermal and mechanical turbulence, the urban atmosphere has low cloud cover and the number of cloudy days based on low cloud cover (low cloud cover ≥ 8 days) far more than in the suburbs. According to statistics from Shanghai in the past ten years (1980-1989), the average low cloud cover in urban areas is 4.0 and in suburban areas is 2.9. The number of cloudy days (low cloud cover ≥ 8) in urban areas is 60 days in a year, while the average number of sunny days (low cloud cover ≤ 2) in suburbs is only 31 days. On the contrary, the number of sunny days (low cloud cover ≤ 2) in urban areas is 132 days, while the average number of sunny days in suburbs is 178 days. In large European and American cities, Similar phenomena have also been observed in Munich, Budapest and New York. Third, due to the large number of pollutants and low cloud cover in the urban atmosphere, the number of sunshine hours is reduced, and the direct solar radiation (S) is greatly weakened. However, due to the large number of scattered particles, the solar scattered radiation (D) is higher than that in dry air. powerful. In terms of regional distribution of atmospheric turbidity expressed as D/S (also known as turbidity factor), urban areas are significantly larger than suburban areas. According to statistical calculations based on Shanghai's observation data in the past 27 years (1959-1985), the turbidity factor in Shanghai's urban areas is on average 15.8% higher than that in its suburbs during the same period. On the Shanghai turbidity factor distribution map, the urban area presents an obvious turbidity island (Figure 8·19, figure omitted). Similar phenomena exist in many foreign cities.

Fourthly, the urban turbidity island effect is also reflected in the fact that visibility in urban areas is lower than in suburban areas. This is because there are many particulate pollutants in the urban atmosphere, which scatter and absorb light, reducing visibility. When the concentration of dioxygen compared to nitrogen NO2 in urban air is extremely high, the sky will appear brown. Against such a sky background, it will be difficult to distinguish the distance of the target, causing visual range obstruction. In addition, in cities, primary pollutants in automobile exhaust gases - nitrogen oxides and hydrocarbons - will form a light blue smog through photochemical reactions under strong sunlight, called photochemical smog, which can cause urban Visibility deteriorates. This phenomenon is seen in cities such as Los Angeles in the United States, Tokyo in Japan, and Lanzhou in my country.

(1) Underlying factors:

1. The impermeable area of ??the underlying surface is large: Except for a small amount of green space in the city, most of them are artificially paved roads, squares, buildings and structures, and the impermeable area of ??the underlying surface is much larger than that of suburban green fields. After a rainfall, rainwater runs away quickly from drainage pipes, so there is less water available for evaporation than in suburban areas. In the energy balance, the net radiation Qn obtained and the latent heat QE used for evapotranspiration are much less than those in the suburbs, while the sensible heat QH used for heating the underlying surface and transporting it to the air is more than that in the suburbs. This makes the underlying surface temperature in the urban area higher than that in the suburbs, forming an "urban underlying surface temperature heat island", and thus makes the urban area warmer than the suburban area through turbulent exchange and long-wave radiation.

2． Thermal properties of the underlying surface: The thermal conductivity K and heat capacity C of the underlying surface in cities are significantly higher than those in suburban areas. There is a lot of heat stored during the day, and the ground cools slower than in the suburbs at night. Through ground-air heat exchange, the temperature in the city is higher than in the suburbs.

3. The geometry of the underlying surface: The buildings in the city are staggered and scattered, forming many "urban street valleys" with different height-to-width ratios.

Under the sun's rays during the day, due to multiple reflections and absorptions between walls and walls and between walls and the ground in street canyons, under other conditions being the same, more solar radiation energy can be obtained than in the suburbs. If the walls and roofs Painting with darker colors will have smaller reflectivity and absorb more solar energy. And because the building materials of walls, roofs and floors have greater thermal conductivity and heat capacity, "urban street canyons" will appear brighter during the day. Absorbing and storing much more heat energy than in suburban areas.

Secondly, in the "urban street canyon", the sky dome visibility (smy view factor, abbreviated as SVF, represented by ) is smaller than that in the open suburbs (Figure 8.21, figure omitted). The long-wave radiation energy at the bottom of the street canyon is In the exchange, in addition to the reverse radiation from the atmosphere, the long-wave reverse radiation value also includes long-wave radiation downward from walls, eaves, etc. Therefore, the heat energy loss of its long-wave net radiation is smaller than that of the suburban wilderness. In addition, the wind speed in urban street valleys is relatively small, and the heat is not easily dissipated. These all lead to the temperature being higher than that of the suburbs.

(2) Anthropogenic heat and greenhouse gases

1. Anthropogenic heat: In mid- and high-latitude cities, especially in winter, the large amount of anthropogenic heat emitted in the city is an important factor in the formation of heat islands. In many cities, the heat island intensity in winter is greater than in the warm season, and the heat island intensity from Monday to Friday is greater than that on weekends, which is affected by this.

2． Greenhouse gases: Due to the large energy consumption in cities, far more greenhouse gases such as CO2 are emitted into the atmosphere than in suburbs, and their humidifying effect is obvious

(3) Weather situation and meteorological conditions

1. Only under stable weather conditions with small pressure gradients is conducive to the formation of urban heat islands. When a strong cold front passes through, there is no heat island phenomenon.

2． When the wind speed is high and the air stratification is unstable, the horizontal and vertical mixing of air between urban and suburban areas is strong, and the temperature difference between urban and suburban areas is not obvious. Generally speaking, the wind speed is low at night, the air stability increases, and the heat island is enhanced.

3. On a cloudless day, the reflectivity difference and long-wave radiation difference between urban and suburban areas are obvious, which is conducive to the formation of heat islands.

(2) Urban heat island effect

According to a large number of observational facts, it is proved that the temperature in cities is often higher than that in surrounding suburbs. Especially when the weather is sunny and windless, the difference △Tu-r (also known as heat island intensity) between the urban temperature Tu and the suburban temperature Tr is greater. For example, in Shanghai at 20:00 on October 22, 1984, the sky was sunny, the wind speed was 1.8m/s, and the temperature in the vast suburbs was around 13°C. Once entering the urban area, the temperature suddenly rose (Figure 8.20, figure omitted), the isotherms were dense, and the temperature The gradient is steep, and the temperature in the old city is above 17°C, like a "heat island" standing on the cooler "ocean" in the countryside. The densely populated areas and factory areas in the city have the highest temperatures, becoming the "peak" of heat islands (also known as heat island centers). The temperature in 62 Middle School in the city center is as high as 18.6°C, which is 5.6°C higher than the suburbs of Chuansha and Jiading, and 6.5°C higher than the outer suburbs of Songjiang. ℃, strong heat islands like this can appear in Shanghai all year round, especially in autumn and winter when the weather is clear and windless.

The heat island effect can be observed in cities of all sizes in the world, regardless of their latitude, sea and land location, or terrain undulations. The heat island intensity is closely related to city size, population density, energy consumption and building density.

There are many factors that contribute to the formation of urban heat islands (see Table 8·10 for details), among which underlying surface factors, man-made heat and greenhouse gas emissions are two aspects affected by human activities. However, in the same city, under different weather conditions and meteorological conditions, the heat island effect is sometimes very obvious (stable weather, no wind), and the heat island intensity can reach around 6℃-10℃, and sometimes it is very weak or not obvious (strong wind, extremely unstable weather). Stablize). Due to the often-present heat island effect, average monthly and annual temperatures in large cities are often higher than those in nearby suburbs.

(3) Urban dry island and wet island effects

In Table 8.8, it is pointed out that the relative humidity in cities is smaller than that in suburbs, and there is an obvious dry island effect. This is a common phenomenon in urban climate. universal characteristics. The impact of cities on water vapor pressure in the atmosphere is more complex. Taking Shanghai as an example, according to the average value of water vapor pressure eu and relative humidity RHu of 11 stations in the urban area in the past 7 years (1984-1990), and the average value of 4 surrounding suburban stations during the same period. Comparison of water vapor pressure er and relative humidity RHr (see Table 8·11)

Relative humidity has obvious daily changes. According to actual measurements, although the absolute values ??of △RHu-r vary, they are all negative. The "urban dry island effect" is present throughout the day. The diurnal variation of △eu-r is different. If the average value is calculated according to the four observation times of the day (02, 08, 14, and 20 o'clock), it is found that at night 02 in most months of the year

< p>City Wet Island". In the warm season from April to November, there is an obvious phenomenon of day and night alternation between dry islands and wet islands, especially in August. Figures 8·22 and 8·23 (figure omitted) show There is an example of day and night alternation between dry island and wet island at 14:00 on August 13, 1984 (urban dry island) and 02:00 on the same day (urban wet island). This kind of phenomenon often occurs in many cities in Europe and the United States during the warm season.