Precipitation that is polluted by acidic gases present in the atmosphere and has a pH value of less than 5.65 is called acid rain. Acid rain is mainly caused by man-made emissions of large amounts of acidic substances into the atmosphere. China's acid rain is mainly due to the formation of a large number of burning high sulfur content of coal, in addition, a variety of motor vehicle emissions from the tailpipe is also an important reason for the formation of acid rain. In recent years, some areas in China have become acid rain-prone areas, and the scope and extent of acid rain pollution has attracted close attention. What is acid? Pure water is neutral, no taste; lemonade, orange juice has a sour taste, vinegar's sour taste is larger, they are weak acids; baking soda water has a slightly astringent alkaline, and caustic soda water is astringent, alkaline taste is larger, caustic soda is alkaline, baking soda is alkaline but belongs to the salts. Scientists found that the size of the acidic flavor and hydrogen ion concentration in aqueous solution; and alkaline flavor and hydroxyl ion concentration in aqueous solution; and then established an indicator: the negative of the logarithm of the concentration of hydrogen ions, called the pH value. Thus, pure water (distilled water) has a pH of 7; the more acidic it is, the lower the pH; the more alkaline it is, the higher the pH. (pH value is generally between 0-14) Unpolluted rain and snow is neutral, pH value is nearly 7; when it is saturated with carbon dioxide in the atmosphere, slightly acidic (water and carbon dioxide combined as carbonic acid), pH value of 5.65. pH value of less than 5.65 of the rain is called acid rain; pH value of less than 5.65 of the snow is called acid snow; in the high altitude or mountains (such as Emei Mountain) on the pervasive fog, the pH value of less than 5.65 is called acid fog.
There are several tools that can be used to test the acidity or alkalinity of water: litmus test ＼ phenolphthalein test ＼ PH test paper (which has a high rate of accuracy and can test the pH value)\PH meter (which can measure a more accurate pH value).
Acid Rain Rate
A number of times in a year, some of which are acid rain and some of which are not, can rain, so the acid rain rate for an area is generally called the number of times acid rain falls in the area divided by the total number of times it falls. The lowest value is 0%; the highest value is 100%. If there is snowfall, it is treated as rainfall.
Sometimes, a rainfall process may last a few days, so the acid rain rate should be a precipitation process as a unit, that is, the acid rain rate for a year of acid rain precipitation process times divided by the total number of precipitation processes throughout the year.
In addition to the annual average precipitation pH, the acid rain rate is another important indicator of whether an area is an acid rain zone.
Acid rain area
Acid rain samples collected in a certain place can not be regarded as acid rain area, because there can be dozens of rains in a year, a certain rain may be acid rain, a certain rain may not be acid rain, so we have to look at the annual average value. At present, the scientific criteria for defining the acid rain zone in China are still under discussion, but it is generally believed that: the annual average precipitation pH value is higher than 5.65, the acid rain rate is 0-20%, for the non-acid rain zone; pH value of 5.30-5.60, the acid rain rate of 10-40%, for the light acid rain zone; pH value of 5.00-5.30, the acid rain rate of 30-60%, for the moderate acid rain zone; pH value of 4.70-5.30, the acid rain rate of 30-60%, for the medium acid rain zone; the average rain value of 4.70-5.30, the acid rain rate of 30%, for the medium acid rain zone. The pH value between 4.70 and 5.00, acid rain rate is 50-80%, is the heavier acid rain area; pH value less than 4.70, acid rain rate is 70-100%, is the heavy acid rain area. This is the so-called five-level standard. In fact, Beijing, Xining, Lanzhou and Urumqi and other cities have also collected a few acid rain, but the average annual pH value and acid rain rate are within the standards of non-acid rain area, so it is a non-acid rain area.
China's two major acid rain areas include (China's acid rain is mainly: sulfuric acid type)
1. Southwest Acid Rain Area: is second only to the Central China Acid Rain Area of precipitation pollution in serious areas.
2. Central China Acid Rain Area: it has now become the largest acid rain pollution in the country, the center of the highest intensity of acid rain pollution area.
Causes Edit Paragraph The cause of acid rain is a complex phenomenon of atmospheric chemistry and atmospheric physics. Acid rain contains a variety of inorganic and organic acids, the vast majority of sulfuric acid and nitric acid. Industrial production, civilian life burning coal emissions out of sulfur dioxide, burning oil and automobile exhaust emissions out of nitrogen oxides, after the "cloud rain process", that is, water vapor condensation in sulfate, nitrate and other condensation nuclei, liquid-phase oxidation reaction occurs, the formation of sulfuric acid droplets and nitric acid droplets; and after the "flushing process under the cloud", that is, the liquid-phase oxidation reaction occurs. "Scouring process under the cloud", that is, acid-containing raindrops in the descending process of continuous merger adsorption, scouring other acid-containing raindrops and acid-containing gases, the formation of larger raindrops, and finally landed on the ground, the formation of acid rain. Since our country burns more coal, the acid rain is sulfuric acid type acid rain. And countries that burn more oil get nitric acid rain.
Acid rain is mostly caused by the combustion of fossil fuels:
(1) S→H2SO4 S+O2 (ignition)→SO2
SO2+H2O→H2SO3 (sulfurous acid)
2H2SO3+O2→2H2SO4 (sulfuric acid)
The total equation of the reaction:
S+O2 (ignition) = SO2,
S+O2 (ignition) = SO2,
S2+O2 (ignition) = SO2,
S2+O2 (ignition) = SO2 ) = SO2,2SO2+2H2O+O2 = 2H2SO4
(2) Oxides of nitrogen dissolve in water to form acids:
a.NO→HNO3(Nitric acid)
2NO+O2=2NO2,3NO2+H2O=2HNO3+NO
The total chemical equation:
4NO+ 2H2O+3O2 = 4HNO3
b.NO2→HNO3
The total chemical reaction equation:
4NO2+2H2O+O2→4HNO3
(*Note: Numbers after the elements are footnotes, and numbers before the chemical formula are stoichiometric numbers.) Factors affecting the formation of acid rainEdit 1.Acidic pollutant emissions and conversion conditions
Generally speaking, the more severe the SO2 pollution in a particular place, the higher the concentration of sulfate ions in the precipitation, resulting in a lower ph value.
2. Atmospheric ammonia
Atmospheric ammonia (NH3) is very important for acid rain formation. Ammonia is the only gas in the atmosphere that appears alkaline when dissolved in water. Because of its water solubility, it can react with acidic aerosols or acids in rainwater to neutralize and reduce acidity. The main sources of ammonia in the atmosphere are the decomposition of organic matter and the volatilization of nitrogen fertilizers applied to agricultural land. The amount of ammonia volatilized from soil increases with the rise of soil pH. In Beijing and Tianjin, soil pH is 7-8 or higher, while in Chongqing and Guiyang, it is generally 5-6, which is one of the important reasons why atmospheric ammonia levels are higher in the north and lower in the south. Where soils are acidic, the buffering capacity for wind and sand dust is low. These two factors together, at least for the time being, can explain the distribution of acid rain in China, which occurs mostly in the south.
3. Particulate matter acidity and its buffering capacity
Atmospheric pollutants, in addition to the acidic gases SO2 and NO2, there is another important member - particulate matter. The sources of particulate matter are complex. The main ones are coal dust and wind-sand dust. The latter accounts for about half in the north and an estimated one-third in the south. The role of particulate matter in the formation of acid rain is twofold: the catalytic metals it contains contribute to the oxidation of SO2 to acid; and it neutralizes the acid. However, if the particulate matter itself is acidic, it will not be able to play a neutralizing role and will become one of the sources of acid. At present, China's atmospheric particulate matter concentration level is generally very high, for the foreign several times to more than ten times, in the acid rain research naturally can not be ignored.
4. The influence of weather conditions
If the meteorological conditions and terrain are favorable for the diffusion of pollutants, the concentration of pollutants in the atmosphere is reduced, acid rain is weakened, and vice versa (such as the phenomenon of inversion of temperature) is aggravated. Hazards of Acid Rain Editorial Sulfur and nitrogen are nutrients. Weakly acidic precipitation dissolves minerals in the ground for plant uptake. Serious harm can occur if the acidity is too high and the pH drops below 5.6. It can directly make a large area of forest death, crop withering; will also inhibit the decomposition of organic matter in the soil and nitrogen fixation, leaching and soil ions combined with calcium, magnesium, potassium and other nutrients, so that the soil barren; can also make the lakes and rivers acidification, and dissolve the soil and the water body sediment in the heavy metals into the water, poisonous to fish; accelerate the corrosion of the buildings and cultural relics and monuments and weathering process; may endanger human health.
The effects of acidic rain are most visible and heavily publicized in Europe and the northeastern United States, but threatened areas also include Canada and perhaps the Sierra region of California, the Rocky Mountains, and China. In some places, rainfall has occasionally been observed to be as acidic as vinegar. The extent of the effects of acid rain is a subject of much debate. Hazards to aquatic life in lakes and rivers were the initial focus of attention, but hazards to buildings, bridges, and equipment are now recognized as additional costly consequences of acid rain. The effects of polluted air on human health are the most difficult to quantify.
The lakes that are most jeopardized are those with poor buffering capacity. When natural alkaline buffers are present, the acidic compounds in acid rain (primarily sulfuric, nitric, and small amounts of organic acids) are neutralized. However, lakes on granitic (acidic) strata are susceptible to direct harm because the acids in rainwater dissolve aluminum and manganese, metal ions. This can cause a reduction in plant and algal growth and, in some lakes, the decline or disappearance of fish populations. Harm to plants caused by this form of pollution ranges from deleterious effects on leaves up to the destruction of fine root systems.
In the northeastern U.S., the main candidates for pollutant reduction are power plants that burn coal with a high sulfur content. Chemical gas washers that prevent pollutant emissions are one possible remedy. A chemical gas scrubber is a device used to treat exhaust gases, or to dissolve, or to precipitate, or to eliminate pollutants. Catalysts that reduce NOx emissions from stationary and mobile sources are another example of the role chemistry can play in improving air quality.
Acid Rain's Loss and Gain Value Meter
Analysis and Calculation Formulas
D=DH+DA+DF+DB+DC+DT
Where,
D - Total Losses due to Atmospheric Pollution
DH- - human health losses due to atmospheric pollution
DA - agricultural losses due to atmospheric pollution
DF - forestry losses due to atmospheric pollution
DB - loss of construction materials due to air pollution
DC - increased cleaning costs due to air pollution
DT - traffic visibility impacted by acid mist Losses
1. Estimation of human losses due to air pollution
DH=DHM+DMT+DHD
Where,
DHM - Losses of medical expenses for respiratory diseases
DMT- - Lost time from work due to respiratory diseases
DHD - Loss of production due to early death of lung cancer patients
2. Estimation of forestry losses due to atmospheric pollution
DA=DAV+DAG
Where,
DAV - loss of reduced vegetable production due to atmospheric pollution
DAG - loss of reduced food production due to atmospheric pollution
3. Estimation of losses to forestry due to atmospheric pollution
DF=DFW+ DFE
Where
DFW - economic loss of timber due to reduction of forest production
DFE - economic loss due to harm of forest ecological benefits (non-forest products)
4.Estimation of loss of construction materials due to atmospheric pollution
4. Estimation of damage to building materials
DB=DBS+DBP
Where
DBS - economic loss of galvanized steel damage
DBP - economic loss of paint damage
5. Estimation of cleaning costs increased by atmospheric pollution
DC=DCH+DCR
Where
DCH - cost of home cleaning
DCR - cleaning of the exterior of urban houses Costs
6. Estimation of Transportation Losses due to Reduced Visibility
DT=DTH+DTW
Where
DTH - Economic Losses due to Acid Mist on Land Transportation
DTW- - economic loss caused by acid mist to water transportation