Science 9Climate and the Earth’s Energy BudgetFor any balanced budget, what comes in must equal what goes out. Otherwise, the planet will either get hotter or cooler. Balancing the global energy budget is a fundamental aspect of the climate system.Consider a beam of sunlight hitting the Earth at the equator as shown below. The beam is approximately at right angles to the Earth's surface, so the amount of Earth it is spread over (area a), is the same as the width of the beam.

Closer to the poles, a beam of the same width covers a much bigger amount of the Earth (area b), because it arrives at a different angle to the Earth's surface. This means that the surface of the Earth receives more energy in the tropics per unit area than it does at the poles. In a similar way, at midday, when the sun is highest in the sky, therefore it feels hottest at midday.

Figure 1. Solar radiation arrives at a different angle to the Earth's surface at the poles than at the equator. In consequence, the area that the beam covers is smallest at the equator and gets larger towards the poles

Some of the incoming solar radiation (which is mainly ultraviolet, visible light and short wavelength infrared) is reflected directly back into space by the atmosphere BUT some is absorbed by the Earth and the atmosphere (see yellow arrows in the diagram). Once the radiation is absorbed, the Earth's surface (and atmosphere) re-emits this energy at a longer wavelength in the form of thermal (or infra-red) radiation.

This figure shows how the distribution of incoming solar (shortwave) and outgoing (longwave) terrestrial radiation varies with latitude (a measure of distance from the equator). The tropics are net absorbers of energy as the amount of absorbed solar energy is greater than the amount of outgoing longwave radiation. Conversely, the poles are constantly losing heat. This should mean that the tropics are constantly heating up and the poles cooling down, but they're not.The Earth must therefore continuously pump heat from the tropics to the poles.

Seasons:Because the sun’s energy is received in its most concentrated form near the equator, the sun generated a tremendous low pressure belt in the tropics. The hot air rises and leaves behind a kind of vacuum that the rest of the air rushes into replace.

Now this is what starts off ALL the worlds winds.The system moves up north and then again down to the south, it wanders around like this because, through the year because the earth’s axis is tilted 23½ degrees The earth rotates on its axis in a counterclockwise direction which causes night and day. It takes 24 hours to complete one rotation. The earth makes one complete revolution around the sun in a counterclockwise direction in 365¼ to complete one year.

At the December Solstice, the direct rays of the sun strike the earth at the Tropic of Capricorn which is 23½° south latitude. The northern hemisphere has the shortest daylight period of the year, and the southern hemisphere has its longest daylight period of the year.

The mid-latitudes of the northern hemisphere are experiencing cool to cold temperatures. At the June Solstice, the reverse occurs. The direct rays of the sun strike at the Tropic of Cancer in the northern hemisphere. It must be remembered that in the mid-latitudes, winter begins in December in the northern hemisphere and summer begins in the southern hemisphere. This is reversed in June.

At the March Equinox, the direct rays of the sun strike the earth at the equator and all parts of the earth experience equal periods of daylight and darkness. This occurs again at the September Equinox. In the mid-latitudes, the seasons called spring and fall are experienced. It must be remembered that the southern hemisphere experiences spring in September and fall in March.

Global Atmospheric CirculationThe circulation of the atmosphere is responsible for about 50% of the transport of energy from the tropics to the poles. The basic mechanism is very simple: hot air rises in the tropics (convection), reducing the pressure at the surface and increasing it higher up. This forces the air to spread away polewards at high levels, and to be drawn in at low levels. As the warm, polewards moving air comes into regions with less incoming solar radiation, it cools and sinks, thus completing the circulation.If the Earth were not rotating, we would see this very simple pattern: hot air would rise in the tropics, move away from the equator, gradually cool, sink at high latitudes near the poles, and finally re-circulate near the surface towards the equator (see figure). If the Earth were not rotating tropical air would rise, travel towards the pole, cool and sink before returning to the equator. The dominant flow at all heights would be along lines of longitude.

Figure 5. Idealisation version of the Earth's atmospheric circulation. Air is heated and rises in the tropics, drifting north before sinking around 30o North and South in the Hadley Cell circulation.

Ocean Surface Currents

The water at the ocean surface is moved primarily by winds that blow in certain patterns because of the Earth’s spin and the Coriolis Effect. Winds are able to move the top 400 meters of the ocean creating surface ocean currents, see the diagram below.

Surface ocean currents flow in a regular pattern, but they are not all the same. Some currents are deep and narrow. Other currents are shallow and wide. Currents are often affected by the shape of the ocean floor. Some move quickly while others move more slowly. A current can also change somewhat in depth and speed over time. Currents move heat around the planet, as water has a HIGH SPECIFIC HEAT CAPACITY, or it holds onto heat very well. It is the oceans that is the world’s HEAT SINK.

Surface ocean currents can be very large. The Gulf Stream, a surface current in the North Atlantic, carries 4500 times more water than the Mississippi River. Each second, ninety million cubic meters of water is

carried past Chesapeake Bay (US) in the Gulf Stream.

Surface ocean currents carry heat from place to place in the Earth system. This affects regional climates. The Sun warms water at the equator more than it does at the high latitude polar regions. The heat travels in surface currents to higher latitudes. A current that brings warmth into a high latitude region will make that region’s climate less chilly. Surface ocean currents form large circular patterns called gyres. Gyres flow clockwise in Northern Hemisphere oceans and counterclockwise in Southern Hemisphere oceans again.

| Major Ocean Currents

What is weather? Weather is the daily state or condition of the atmosphere. Weather is a very temporary condition. Put quite simply, weather is what hits you in the face when you walk outside.

Climate is the average yearly pattern of weather conditions. The key word in the definition is average. Climate is usually described in terms of annual precipitation patterns and amounts and annual temperature patterns of highs and lows. Climate cannot be experienced by walking outside. To experience climate, one must live in a location for more than a year. One must always remember that averages often disguise the extremes. For example, if the average yearly temperature of a location is reported as 50 degrees, it could mean that the average high is 100 degrees and the average low is zero degrees, or it could mean that the average high is 52 degrees and the average low is 48 degrees.

It will be difficult to study one of these factors without referring to one or more of the other factors since they often operate in combination. It is possible that one factor might influence a place to one climatic extreme and that another factor might influence it toward the opposite condition. The result may be a moderated condition between the two extremes. An example would be the climates of Ireland and Great Britain. Their latitude would incline them toward very cold temperatures, particularly in the winter. These are islands in a very large body of water, there is a large, warm ocean current, The Gulf Stream, as water has a very high heat capacity.These winds are warmed by the warm ocean current and bring warmer than would be expected temperatures to these islands which are located at fairly high latitudes. They are so far north that their climate should be far colder, but the Gulf Stream ocean current counteracts the influence of latitude.

Winds:Winds may bring either warmer or cooler temperatures, depending on the direction from which the wind blows. What is wind, and what causes it? Winds result partly from the fact that some parts of the world become hotter than others. Hotter areas are called low pressure areas because as air is heated, it expands becomes lighter and rises. As air loses heat [cools], it contracts or shrinks and becomes heavier (it contains more gas molecules per unit of volume) and, therefore, it moves downward in the atmosphere. Wind, then, is defined as the horizontal

movement of air at the earth’s surface from areas of high pressure to areas of low pressure where the air is rising.

A generalized system of wind belts tries to establish itself on the earth. The distribution of land and water on the earth, and the resulting variances in temperatures and pressures somewhat disrupts the idealized system of wind belts. This is NOT how the wind is everyday, it is very random, but it is an idea.

Green house Effect:The Greenhouse EffectLike an ordinary greenhouse, retain energy radiated into it from outside. The greenhouse analogy isn't very exact, but the name certainly stuck. Certain gases, including water vapour and carbon dioxide (CO2), don't affect visible light but absorb longer wavelength radiation (infrared). He suggested that these gases insulate the Earth.

Visible incoming sunlight either gets reflected (for example by clouds or aerosols and SO2 pollution s), absorbed (for example by gaseous water vapour), or passes unhindered through the atmosphere, and gets absorbed by the surface of the Earth. Thus heating the earth. (a small fraction is reflected from the surface, particularly for bright surfaces such as fresh snow or deserts, known as albedo).

The Earth radiates heat from the surface back into the atmosphere, where it can pass back into space, or, because it has now got a longer wavelength than the shorter wavelengths from the sun that was able to pass through the atmosphere, these longer wavelengths cannot pass as easily out of the atmosphere. This infa-red waves or heat, gets temporarily absorbed by the water vapour, carbon dioxide, methane and other greenhouse gases which are present in the atmosphere. As the water vapour/ methane/ carbon dioxide molecules absorb the longwave radiation, they heat up, and in turn re-radiate long wave radiation in all directions. Some is lost to space, but some of it also gets radiated back to the surface, again warming it.

This naturally occurring process helps keep the Earth warm enough for liquid water to exist. Without greenhouse gases, the average temperature at the Earth's surface would be 33oC colder than it actually is. As the average global temperature is only 15 C , if we fell 33 C we’d be a frozen planet forever, much like Mars.

Now, what if the concentrations of these insulating gases increase? We might expect the process described above to intensify. In fact, this is just what the Nobel Prize-winning Swedish chemist Svante Arrhenius did in 1896. By knowing how CO2 absorbs heat radiation from the surface of the Earth, he calculated what would happen if the amount of CO2 were doubled.

He estimated that a doubling of CO2 would lead to an average global surface temperature increase of 2oC, not a great estimate, as modern temperatures have only gone up 0.70 oC after we have doubled our CO2 from 200 ppm to 400 ppm.

This approach, while only a handy first guess, considers the climate system in the absence of any feedback processes. Sometimes feedback processes act to offset or inhibit a change (negative feedback), and sometimes they act to amplify a change (positive feedback). There are many examples of feedbacks in the climate system. If the atmosphere gets warmer, ice melts. Ice reflects a lot of incoming solar radiation, so if it melts, less gets reflected, more gets absorbed by the Earth and the atmosphere gets warmer; a positive feedback. On the other hand, if there is more carbon dioxide in the atmosphere, some plants grow faster, absorbing more CO2 and reducing it in the atmosphere; a negative feedback.

What is eutrophication? Causes, effects and control

Algal bloom in 2010 along the coast of Qingdao, eastern)Eutrophication is an abnormal growth of algae. Eutrophication is an enrichment of water by nutrient salts that causes structural changes to the ecosystem such as: increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality.” Eutrophication process consists of a continuous increase in the contribution of nutrients, mainly nitrogen and phosphorus (organic load) until it exceeds the capacity of the water body (i.e. the capacity of a lake, river or sea to purify itself) , triggering structural changes in the waters.These structural changes mainly depend on 2 factors:

Use of fertilisers: Agricultural practices and the use of fertilisers in the soil contribute to the accumulation of nutrients. When these nutrients reach high concentration levels and the ground is no longer able to assimilate them, they are carried by rain into rivers and groundwater that flow into lakes or seas.

Example of fertiliser spreading on agricultural landDischarge of waste water into water bodies

In various parts of the world, and particularly in developing countries, waste water is discharged directly into water bodies such as rivers, lakes and seas. The result of this is the release of a high quantity of nutrients which stimulates the disproportionate growth of algae. In industrialised countries, on the other hand, waste water can be illegally discharged directly into water bodies. When instead water is treated by means of water treatment plants before discharge into the environment, the treatments applied are not always such as to reduce the organic load, with the consequent accumulation of nutrients in the ecosystem.

Example of discharge of waste water into a reservoirEutrophication is characterised by a significant increase of algae (microscopic organisms similar to plants) due to the greater availability of one or more growth factors necessary for photosynthesis, such as sunlight, carbon dioxide and nutrients (nitrogen and phosphorus). When algae start to grow in an uncontrolled manner, an increasingly large biomass is formed which is destined to degrade. In deep water, a large amount of organic substance accumulates, represented by the algae having reached the end of their life cycle. To destroy all the dead algae, an excessive consumption of oxygen is required, in some cases almost total, by microorganisms. An anoxic (oxygen-free) environment is thus created on the lake bottom, with the growth of organisms capable of living in the absence of oxygen (anaerobic), responsible for the degradation of the biomass. The microorganisms, decomposing the organic substance in the absence of oxygen, free compounds that are toxic, such as ammonia and hydrogen sulphide (H2S). The absence of oxygen reduces biodiversity causing, in certain cases, even the death of animal and plant species. All this happens when the rate of degradation of the algae by microorganisms is greater than that of oxygen regeneration, which in summer is already present in low concentrations.

Eutrophication process representation (Feem re-elaboration from Arpa Umbria, 2009)EffectsThe disturbance of aquatic equilibria may be more or less evident according to the enrichment of water by nutrients (phosphorus and nitrogen). An aquatic environment with a limited availability of phosphorus and nitrogen is described as “oligotrophic” while one with high availability of these elements is called “eutrophic”; a lake with intermediate availability is called “mesotrophic”.When the eutrophication phenomenon becomes particularly intense, undesirable effects and environmental imbalances are generated. The two most acute phenomena of eutrophication are hypoxia in the deep part of the lake (or lack of oxygen) and algal blooms that produce harmful toxins, processes that can destroy aquatic life.

Fish mortality

Water is not a commercial product like any other but rather a heritage which must be defended and protected, especially in the presence of a global decline in the availability of drinking water and increase in its demand.Despite the considerable efforts made to improve the water quality by limiting nutrient enrichment, cultural eutrophication and the resulting algal blooms continue to be the main cause of water pollution. The prevention and protection action that countries must adopt to safeguard the quality of surface water as requested not only by the scientific community.Management of the eutrophic process is a complex issue that will require the collective efforts of scientists, policy makers and citizens.

The Ozone Hole

For nearly a billion years, ozone molecules in the atmosphere have protected life on Earth from the effects of ultraviolet rays. The ozone layer resides in the stratosphere and surrounds the entire Earth. UV-B radiation (280- to 315- nanometer (nm) wavelength) from the Sun is partially absorbed in this layer.

As a result, the amount of UV-B reaching Earth’s surface is greatly reduced. Human exposure to UV-B increases the risk of skin cancer, cataracts, and a suppressed immune system. UV-B exposure can also damage terrestrial plant life, single cell organisms, and aquatic ecosystems.

UV-A (315- to 400-nm wavelength) and other solar radiation are not strongly absorbed by the ozone layer.

In the past 60 years or so human activity has contributed to the deterioration of the ozone layer.

Only 10 or less of every million molecules of air are ozone. The majority of these ozone molecules resides in a layer between 10 and 40 kilometers (6 and 25 miles) above the Earth's surface in the stratosphere.

Each spring in the stratosphere over Antarctica (Spring in the southern hemisphere is from September through November.), atmospheric ozone is rapidly destroyed by chemical processes involving CFC’s (chlorofluorocarbon release from air condition units) .As winter arrives, a vortex of winds develops around the pole and isolates the polar stratosphere. When temperatures drop below -78°C (-109°F), thin clouds form of ice, nitric acid, and sulphuric acid mixtures. Chemical reactions on the surfaces of ice crystals in the clouds release active forms of CFCs. Ozone depletion begins, and the ozone “hole” appears. Over the course of two to three months, approximately 50% of the total column amount of ozone in the atmosphere disappears. At some levels, the losses approach 90%. This has come to be called the Antarctic ozone hole.In spring, temperatures begin to rise, the ice evaporates, and the ozone layer starts to recover.

The ozone "hole" is really a reduction in concentrations of ozone high above the earth in the stratosphere. ozone hole has steadily grown in size (up to 27 million sq. km.) and length of existence (from August through early December) over the past two decades. After a series of rigorous meetings and negotiations, the Montreal Protocol on Substances that Deplete the Ozone Layer was finally agreed upon on 16 September 1987 at the Headquarters of the International Civil Aviation Organization in Montreal. The Montreal Protocol stipulates that the production and consumption of compounds that deplete ozone in the stratosphere--chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform--are to be phased out by 2000 (2005 for methyl chloroform). Scientific theory and evidence suggest that, once emitted to the atmosphere, these compounds could significantly deplete the stratospheric ozone layer that shields the planet from damaging UV-B radiation. Man-made chlorines, primarily chloroflourobcarbons (CFCs), contribute to the thinning of the ozone layer and allow larger quantities of harmful ultraviolet rays to reach the earth.

Consumption of ozone depleting substances expressed as million tonnes of ozone depletion potential (ODP), 1989-2009.

Acid Rain

The effects of acid rain are evident in New York's Adirondack Mountains, in Germany's Black Forest and industrial urban areas around the world. The picture is not a pretty one. It includes stands of dying trees, lakes uninhabitable by fish and weathered and damaged historic architecture.

Acid rain has not caused such severe problems in the places mentioned above. However, it is still an air pollution issue that generates concern among our residents. Frequently asked questions are: How bad is the problem in the state? What are the causes?

The pH of Acid Rain

Chemists use pH (potential of Hydrogen) to measure the concentration of hydrogen ions in a chemical solution to determine how acidic or basic the solution is. The pH scale measures how acidic or basic a substance is. It ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic. Each whole pH value below 7 is ten times more acidic than the next higher value. For example, a pH of 4 is ten times more

acidic than a pH of 5 and 100 times (10 times 10) more acidic than a pH of 6. The same holds true for pH values above 7, each of which is ten times more basic than the next lower whole value. For example, a pH of 10 is ten times more basic than a pH of 9.

Chemicals that are very basic or very acidic are called "reactive." These chemicals can cause severe burns. Automobile battery acid is an acidic chemical that is reactive. Automobile batteries contain a stronger form of some of the same acid that is in acid rain. Household drain cleaners often contain lye, a strong base that is reactive.

When equal strength bases and acids are mixed they neutralize each other. The resulting solution is water and a salt. Remember, a salt is defined as a metal combined with a non-metal so chances are that it will not be sodium chloride (table salt). A substance that is neither acidic nor basic is neutral.

Normal rain is slightly acidic because carbon dioxide dissolves into it so it has a pH of about 5.5. As the rain (H2O) falls through the atmosphere and combines with the carbon dioxide (CO2) it creates mild carbonic acid (H2CO3).

Kinds of Acid Rain

"Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry.

Wet deposition refers to acidic rain, fog, hail, dew and snow. Acidic water affects a variety of plants and animals as it flows over and through the ground. The strength of the effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved. Buffering capacity is the soils ability to resist chemical change. Affects also depends on the types of fish, trees, and other living things that rely on the water.

Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain making the combination more acidic than the falling rain alone.

Prevailing winds blow the compounds that cause both wet and dry acid deposition across state and national borders, and sometimes over hundreds of miles. Acid rain can affect us here in Baraboo.

What is Acid Rain? Where Does It Come From?

Pure rain is naturally slightly acidic a pH of 5.6. The slight natural acidity of pure rain is the result of carbon dioxide in the air dissolving in water to produce a weak carbonic acid solution. This natural acid in rainfall and snowmelt is partly responsible for the slow weathering of soil and rocks.

Acid rain, however, is the result of sulfur dioxide and nitrogen oxides entering the atmosphere. These two pollutants are mainly produced by human activities. Sulfur dioxide is most commonly produced by coal-fired power plants and factories. Scientists have also confirmed that about 2/3 of all sulfur dioxide (SO2) and 1/4 of all nitrogen oxides (NOx) comes from electric power generation that relies on burning fossil fuels like coal. Nitrogen oxides are products of motor vehicles and off-road engines, coal-fired power plants and factories (such as pulp and paper mills in Wisconsin) and home furnaces.

Acid rain is formed when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid (H2SO4) and nitric acid (HNO3). Once these chemicals are released into the atmosphere they combine with moisture, change chemically, and return to earth in the form of acidic deposition. Acidic deposition also may occur in a dry form when acidic compounds attach to particulates (dust) and return to earth. These acids can overwhelm the neutralizing capacity of some soils and lake water. Simply stated, the environment is sometimes unable to defend itself against the effects of these acids.

Aquatic Resources

Many factors affect whether acidification, due to acid rain, occurs in bodies of water. Bodies of water that are low in acid neutralizing capacity (ANC) are considered especially vulnerable to the effects of acid rain. Soils in are derived from granite bedrock so they have low acid neutralizing capacity due to the lack of carbonates. Carbonates are basic so they neutralize the acid. Parts that have primarily sandstone and limestone bedrock based soils have a high acid neutralizing capacity because the limestone bedrock is a carbonate.A body of water is more likely to become acidic if it does not have any acid neutralizing capacity. That does not, however, mean that it is already devoid of fish and other aquatic life. As a body of water becomes more acidic, it loses some of its biodiversity as the more acid-sensitive species of plant and animal life die off or experience a decrease in reproductive success. The degree of threat from acid rain depends on the vulnerability of plant and animal species in that body of water to an acidic environment.Health Effects

A direct effect of acid deposition on human health results from exposure to acid aerosols inhaled from the surrounding air. Acid aerosols are mixtures of several different pollutants including particles (large and small), strong acids (e.g. sulfuric acid), weak acids and vapors (e.g. nitric acid). Long-term exposure to acid aerosols is known to damage lung tissue and contribute to the development of respiratory diseases such as asthma and chronic bronchitis, especially in children and the elderly.Acid deposition also has been connected to elevated mercury concentrations in fish and fish-eating wildlife such as the common loon, mink, otter, and eagles. Researchers believe that acidification of bodies of water increases the formation and movement of methylmercury, a toxic form of mercury, into the aquatic food chain. This also endangers the health of people, especially infants, children, and fetuses carried by women who eat contaminated fish.

Exposure of humans to mercury may result in damage to the kidneys, brain and central nervous system. It may also cause developmental defects. Recent research indicates that prenatal exposure to mercury concentrations much lower than the current "safe" levels established by the World Health Organization may result in subtle neurological defects in children, such as abnormal reflexes and delayed motor skill development. Arsenic is another heavy metal that is released by acidic water flowing through the ground. Arsenic is commonly used as rat poison.The pH levels of rain in the state have been low enough to cause damage to building materials such as paint, stone, mortar and metals. An example of this is when marble changes to gypsum when exposed to acid rain. The gypsum molecule is much larger and softer than the original marble molecule resulting in weakened building stones and flaking of building materials. In addition to damaging building materials, acid rain can also cause increased weathering of historic structures and outdoor art objects.

What Can You Do to Help?

Using electrical energy wisely could have a significant impact because a lot of the emissions that contribute to acid rain originate from coal-burning electric power plants. You can reduce electrical use in a number of ways:

Insulate your home so it is more energy efficient during the winter and the summer. Replace your heating system if it is over 25 years old.

Keep the thermostat down in the winter.Open windows and use fans instead of the air conditioner during the summer.

Use energy-efficient compact fluorescent bulbs instead of incandescent ones and turn off lights when not in use.Purchase energy efficient appliances, especially those that use large amounts of electricity such as hot water heaters, ranges, dryers and refrigerators.Turn off electric appliances, such as computers, when you aren't using them and make sure that they run as efficiently as possible.

Driving a fuel-efficient vehicle and driving less overall both help because motor vehicle exhaust is a significant source of nitrogen oxide emissions.

With a combination of education and action, can continue to reduce acid rain and help preserve the natural beauty of the state for generations to come.

Secondary Pollutants

Another form of air pollution is formed when smoke and fog are combined to make smog. The two common types of smog are photochemical smog and sulfurous smog. Secondary pollutants are damaging to humans and plant life. Large cities often have hazy blankets of smog covering them. Some cities have “smog alert” days where they recommend being outside for only very short periods of time. Mexico City, Milwaukee, Denver, Los Angeles, New York and Phoenix all have smog alert days. What we typically call smog is primarily made up of ground-level ozone (O3) mixed with other chemicals. Ground-level ozone is the main harmful ingredient in smog. Ozone causes breathing difficulties, headaches, fatigue and can aggravate respiratory problems.

Photochemical smog forms when sunlight reacts with nitrogen and oxygen in the air. Burning fossil fuels, such as, oil, natural gas and gasoline in automobiles, factories and airplanes release nitrogen and oxygen into the air. The nitrogen and oxygen reacts with the sunlight to chemically combine forming NO x which creates a brown haze in the air. The NOx can attach to water molecules to form mild nitric acid (HNO3) that slowly erodes buildings and other structures.Catalytic converters in automobiles reduce air pollution by oxidizing hydrocarbons to CO2 and H2O.They also convert nitrogen oxides to N2 and O2 to prevent the formation of smog.

Sulfurous smog forms when sunlight reacts with sulfur and oxygen in the air forming sulfur compounds (SOx). Burning coal to generate electricity releases sulfur compounds, dust and smoke particles into the air forming a gray haze in the air. When the air is stagnant, not moving, over an area the sulfurous smog develops. Mixing sulfurous smog with water molecules creates a weak sulfuric acid (H2SO4) that eats away at buildings and other structures.