Air pollution occurs when harmful or excessive quantities of substances including gases and biological molecules are introduced into Earth's atmosphere. It may cause diseases and death to humans. Both human activity and natural processes can generate air pollution. Indoor air pollution and poor urban air quality are listed as two of the world's worst toxic pollution problems in the 2008 Blacksmith Institute World's Worst Polluted Places report. According to the 2014 World Health Organization report, air pollution in 2012 caused the deaths of around 7 million people worldwide, an estimate echoed by one from the International Energy Agency. An air pollutant is a material in the air that can have adverse effects on the ecosystem; the substance can be liquid droplets, or gases. A pollutant can be of man-made. Pollutants are classified as secondary. Primary pollutants are produced by processes such as ash from a volcanic eruption. Other examples include carbon monoxide gas from motor vehicle exhausts or sulphur dioxide released from the factories.
Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants interact. Ground level ozone is a prominent example of secondary pollutants; some pollutants may be both primary and secondary: they are both emitted directly and formed from other primary pollutants. Substances emitted into the atmosphere by human activity include: Carbon dioxide – Because of its role as a greenhouse gas it has been described as "the leading pollutant" and "the worst climate pollution". Carbon dioxide is a natural component of the atmosphere, essential for plant life and given off by the human respiratory system; this question of terminology has practical effects, for example as determining whether the U. S. Clean Air Act is deemed to regulate CO2 emissions. CO2 forms about 410 parts per million of earth's atmosphere, compared to about 280 ppm in pre-industrial times, billions of metric tons of CO2 are emitted annually by burning of fossil fuels. CO2 increase in earth's atmosphere has been accelerating.
Sulfur oxides – sulphur dioxide, a chemical compound with the formula SO2. SO2 is produced in various industrial processes. Coal and petroleum contain sulphur compounds, their combustion generates sulphur dioxide. Further oxidation of SO2 in the presence of a catalyst such as NO2, forms H2SO4, thus acid rain; this is one of the causes for concern over the environmental impact of the use of these fuels as power sources. Nitrogen oxides – Nitrogen oxides nitrogen dioxide, are expelled from high temperature combustion, are produced during thunderstorms by electric discharge, they can be seen as a plume downwind of cities. Nitrogen dioxide is a chemical compound with the formula NO2, it is one of several nitrogen oxides. One of the most prominent air pollutants, this reddish-brown toxic gas has a characteristic sharp, biting odor. Carbon monoxide – CO is a colorless, toxic yet non-irritating gas, it is a product of combustion of fuel such as natural coal or wood. Vehicular exhaust contributes to the majority of carbon monoxide let into our atmosphere.
It creates a smog type formation in the air, linked to many lung diseases and disruptions to the natural environment and animals. In 2013, more than half of the carbon monoxide emitted into our atmosphere was from vehicle traffic and burning one gallon of gas will emit over 20 pounds of carbon monoxide into the air. Volatile organic compounds – VOCs are a well-known outdoor air pollutant, they are categorized as either non-methane. Methane is an efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are significant greenhouse gases because of their role in creating ozone and prolonging the life of methane in the atmosphere; this effect varies depending on local air quality. The aromatic NMVOCs benzene and xylene are suspected carcinogens and may lead to leukemia with prolonged exposure. 1,3-butadiene is another dangerous compound associated with industrial use. Particulate matter / particles, alternatively referred to as particulate matter, atmospheric particulate matter, or fine particles, are tiny particles of solid or liquid suspended in a gas.
In contrast, aerosol refers to gas. Some particulates occur originating from volcanoes, dust storms and grassland fires, living vegetation, sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes generate significant amounts of aerosols. Averaged worldwide, anthropogenic aerosols—those made by human activities—currently account for 10 percent of our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer. Particulates are related to respiratory infections and can be harmful to those suffering from conditions like asthma. Persistent free radicals connected to airborne fine particles are linked to cardiopulmonary disease. Toxic metals, such as lead and mercury their compounds. Chlorofluorocarbons – harmful to the ozone layer; these are gases which are released from air conditioners, aerosol sprays, etc. On release into the air, CFCs rise to the stratosphere.
Here they come in contact with other gases and
Siding or wall cladding is the protective material attached to the exterior side of a wall of a house or other building. Along with the roof, it forms the first line of defense against the elements, most sun, rain/snow and cold, thus creating a stable, more comfortable environment on the interior side; the siding material and style can enhance or detract from the building's beauty. There is a wide and expanding variety of materials to side with, both natural and artificial, each with its own benefits and drawbacks. Masonry walls as such do not require siding. Walls that are internally framed, whether with wood, or steel I-beams, must always be sided. Most siding consists of pieces of weather-resistant material that are smaller than the wall they cover, to allow for expansion and contraction of the materials due to moisture and temperature changes. There are various styles of joining the pieces, from board and batton, where the butt joints between panels is covered with a thin strip of wood, to a variety of clapboard called lap siding, in which planks are laid horizontally across the wall starting from the bottom, building up, the board below overlapped by the board above it.
These techniques of joinery are designed to prevent water from entering the walls. Siding that does not consist of pieces joined together would include stucco, used in the Southwest, it is applied over a lattice, just like plaster. However, because of the lack of joints, it cracks and is susceptible to water damage. Rainscreen construction is used to improve siding's ability to keep walls dry. Thatch is an ancient and widespread building material used on roofs and walls. Thatch siding is made with dry vegetation such as water reeds, or combed wheat reed; the materials are weaved in patterns designed to deflect and direct water. Wood siding is versatile in style and can be used on a wide variety of building structures, it can be stained in any color palette desired. Though installation and repair is simple, wood siding requires more maintenance than other popular solutions, requiring treatment every four to nine years depending on the severity of the elements to which it is exposed. Ants and termites are a threat to many types of wood siding, such that extra treatment and maintenance that can increase the cost in some pest-infested areas.
Wood is biodegradable. However, most paints and stains used to treat wood are not environmentally friendly and can be toxic. Wood siding can provide some minor insulation and structural properties as compared to thinner cladding materials. Wood shingles or irregular cedar "shake" siding was used in early New England construction, was revived in Shingle Style and Queen Anne style architecture in the late 19th century. Wood siding in overlapping horizontal rows or "courses" is called clapboard, weatherboard, or bevel siding, made with beveled boards, thin at the top edge and thick at the butt. In colonial North America, Eastern white pine was the most common material. Wood siding can be made of rot-resistant woods such as redwood or cedar. Jointed horizontal siding may be tongue and grooved. Drop siding comes in a wide variety including Dutch Lap and log siding. Vertical siding may have a cover over the joint: board and batten, popular in American wooden Carpenter Gothic houses. Plywood sheet siding is sometimes used on inexpensive buildings, sometimes with grooves to imitate vertical shiplap siding.
One example of such grooved plywood siding is the type called Texture 1-11 T1-11 or T111. There is a product known as reverse board-and-batten RBB that looks similar but has deeper grooves; some of these products may be thick enough and rated for structural applications if properly fastened to studs. Both T-11 and RBB sheets are quick and easy to install as long as they are installed with compatible flashing at butt joints. Slate shingles may be simple in form but many buildings with slate siding are decorative. Wood clapboard is imitated using vinyl siding or uPVC weatherboarding, it is produced in units twice as high as clapboard. Plastic imitations of wood shingle and wood shakes exist. Since plastic siding is a manufactured product, it may come in unlimited color styles. Vinyl sidings would fade and buckle over time, requiring the siding to be replaced. However, newer vinyl options have resist damage and wear better. Vinyl siding is sensitive to direct heat from barbecues or other sources. Unlike wood, vinyl siding does not provide additional insulation for the building, unless an insulation material has been added to the product.
It has been criticized by some fire safety experts for its heat sensitivity. This sensitivity makes it easier for a house fire to jump to neighboring houses in comparison to materials such as brick, metal or masonry. Vinyl siding has a potential environmental cost. While vinyl siding can be recycled, it cannot be burned. If dumped in a landfill, plastic siding does not break down quickly. Vinyl siding is considered one of the more unattractive siding choices by many. Although newer options and proper installation can eliminate this complaint, vinyl siding has visible seam lines between panels and do not have the quality appea
United States Department of Energy
The United States Department of Energy is a cabinet-level department of the United States Government concerned with the United States' policies regarding energy and safety in handling nuclear material. Its responsibilities include the nation's nuclear weapons program, nuclear reactor production for the United States Navy, energy conservation, energy-related research, radioactive waste disposal, domestic energy production, it directs research in genomics. DOE sponsors more research in the physical sciences than any other U. S. federal agency, the majority of, conducted through its system of National Laboratories. The agency is administered by the United States Secretary of Energy, its headquarters are located in Southwest Washington, D. C. on Independence Avenue in the James V. Forrestal Building, named for James Forrestal, as well as in Germantown, Maryland. Former Governor of Texas Rick Perry is the current Secretary of Energy, he was confirmed by a 62 to 37 vote in the United States Senate on March 2, 2017.
In 1942, during World War II, the United States started the Manhattan Project, a project to develop the atomic bomb, under the eye of the U. S. Army Corps of Engineers. After the war in 1946, the Atomic Energy Commission was created to control the future of the project. Among other nuclear projects, the AEC produced fabricated uranium fuel cores at locations such as Fernald Feed Materials Production Center in Cincinnati, Ohio. In 1974, the AEC gave way to the Nuclear Regulatory Commission, tasked with regulating the nuclear power industry, the Energy Research and Development Administration, tasked to manage the nuclear weapon, naval reactor, energy development programs; the 1973 oil crisis called attention to the need to consolidate energy policy. On August 4, 1977, President Jimmy Carter signed into law The Department of Energy Organization Act of 1977, which created the Department of Energy; the new agency, which began operations on October 1, 1977, consolidated the Federal Energy Administration, the Energy Research and Development Administration, the Federal Power Commission, programs of various other agencies.
Former Secretary of Defense James Schlesinger, who served under Presidents Nixon and Ford during the Vietnam War, was appointed as the first secretary. In December 1999, the FBI was investigating. Wen Ho Lee was accused of stealing nuclear secrets from Los Alamos National Laboratory for the People's Republic of China. Federal officials, including then-Energy Secretary Bill Richardson, publicly named Lee as a suspect before he was charged with a crime; the U. S. Congress held hearings to investigate the Department of Energy's mishandling of his case. Republican senators thought that an independent agency should be in charge of nuclear weapons and security issues, not the Department of Energy. All but one of the 59 charges against Lee were dropped because the investigation proved that the plans the Chinese obtained could not have come from Lee. Lee won a $1.6 million settlement against the federal government and news agencies. In 2001, American Solar Challenge was sponsored by the United States Department of Energy and the National Renewable Energy Laboratory.
After the 2005 race, the U. S. Department of Energy discontinued its sponsorship. Title XVII of Energy Policy Act of 2005 authorizes the DOE to issue loan guarantees to eligible projects that "avoid, reduce, or sequester air pollutants or anthropogenic emissions of greenhouse gases" and "employ new or improved technologies as compared to technologies in service in the United States at the time the guarantee is issued". In loan guarantees, a conditional commitment requires to meet an equity commitment, as well as other conditions, before the loan guarantee is completed; the United States Department of Energy, the Nuclear Threat Initiative, the Institute of Nuclear Materials Management, the International Atomic Energy Agency partnered to develop and launch the World Institute for Nuclear Security in September 2008. WINS is an international non-governmental organization designed to provide a forum to share best practices in strengthening the security and safety of nuclear and radioactive materials and facilities.
On March 28, 2017 a supervisor in the Office of International Climate and Clean Energy asked staff to avoid the phrases "climate change," "emissions reduction," or "Paris Agreement" in written memos, briefings or other written communication. A DOE spokesperson denied; the department is under the control and supervision of a United States Secretary of Energy, a political appointee of the President of the United States. The Energy Secretary is assisted in managing the department by a United States Deputy Secretary of Energy appointed by the president, who assumes the duties of the secretary in his absence; the department has three under secretaries, each appointed by the president, who oversee the major areas of the department's work. The president appoints seven officials with the rank of Assistant Secretary of Energy who have line management responsibility for major organizational elements of the Department; the Energy Secretary assigns their duties. Excerpt from the Code of Federal Regulations, in Title 10: Energy:The official seal of the Department of energy "includes a green shield bisected by a gold-colored lightning bolt, on, emblazoned a gold-colored symbolic sun, oil derrick and dynamo.
It is crested atop a white rope. Both appear on a blue field surrounded by concentric circles in which the name
Arizona State University
Arizona State University is a public metropolitan research university on five campuses across the Phoenix metropolitan area, four regional learning centers throughout Arizona. ASU is one of the largest public universities by enrollment in the U. S; as of fall 2018, the university had about 80,000 students attending classes across its metro campuses, including 66,000-plus undergraduates and more than 12,000 postgraduates. The university is organized into 17 colleges, featuring more than 170 cross-discipline centers and institutes. ASU offers 350 degree options for undergraduates students, as well as more than 400 graduate degree and certificate programs. ASU has nearly 600 ASU scholar-athletes across 26 varsity-level sports; the Arizona State Sun Devils compete in the Pac-12 Conference and have won 59 Pac-10/Pac-12 championships dating to 1979, have captured 24 NCAA championships dating to its first title in 1965. In addition to its athletic program, the university is home to over 1,100 registered student organizations.
ASU's charter, approved by the board of regents in 2014, is based on the "New American University" model created by ASU President Michael M. Crow upon his appointment as the institution's 16th president in 2002, it defines ASU as "a comprehensive public research university, measured not by whom it excludes, but rather by whom it includes and how they succeed. Since 2005, ASU has been ranked among the top research universities in the U. S. public and private, based on research output, development, research expenditures, number of awarded patents and awarded research grant proposals. The 2019 university ratings by U. S. News & World Report rank ASU No. 1 among the Most Innovative Schools in America for the fourth year in a row. U. S. News & World Report shows 84% of the student applications get accepted. A diverse faculty of more than 4,400 scholars includes 4 Nobel laureates, 6 Pulitzer Prize winners, 4 MacArthur Fellows Program "Genius Grant" members and 19 National Academy of Sciences members.
Additionally, among the faculty are 180 Fulbright Program American Scholars, 72 National Endowment for the Humanities fellows, 38 American Council of Learned Societies fellows, 36 members of the Guggenheim Fellowship, 21 members of the American Academy of Arts and Sciences, 9 National Academy of Engineering members and 3 National Academy of Medicine members. The National Academies has bestowed "highly prestigious" recognition on 227 ASU faculty members. Arizona State University was established as the Territorial Normal School at Tempe on March 12, 1885, when the 13th Arizona Territorial Legislature passed an act to create a normal school to train teachers for the Arizona Territory; the campus consisted of a single, four-room schoolhouse on a 20-acre plot donated by Tempe residents George and Martha Wilson. Classes began with 33 students on February 8, 1886; the curriculum evolved over the years and the name was changed several times. In 1923, the school stopped offering high school courses and added a high school diploma to the admissions requirements.
In 1925, the school became the Tempe State Teachers College and offered four-year Bachelor of Education degrees as well as two-year teaching certificates. In 1929, the 9th Arizona State Legislature authorized Bachelor of Arts in Education degrees as well, the school was renamed the Arizona State Teachers College. Under the 30-year tenure of president Arthur John Matthews, the school was given all-college student status; the first dormitories built in the state were constructed under his supervision in 1902. Of the 18 buildings constructed while Matthews was president, six are still in use. Matthews envisioned an "evergreen campus," with many shrubs brought to the campus, implemented the planting of 110 Mexican Fan Palms on what is now known as Palm Walk, a century-old landmark of the Tempe campus. During the Great Depression, Ralph Waldo Swetman was hired to succeed President Matthews, coming to Arizona State Teachers College in 1930 from Humboldt State Teachers College where he had served as president.
He served a three-year term. During his tenure, enrollment at the college doubled. Matthews conceived of a self-supported summer session at the school at Arizona State Teachers College, a first for the school. In 1933, Grady Gammage president of Arizona State Teachers College at Flagstaff, became president of Arizona State Teachers College at Tempe, beginning a tenure that would last for nearly 28 years, second only to Swetman's 30 years at the college's helm. Like President Arthur John Matthews before him, Gammage oversaw the construction of several buildings on the Tempe campus, he guided the development of the university's graduate programs. During his presidency, the school's name was changed to Arizona State College in 1945, to Arizona State University in 1958. At the time, two other names were considered: Tempe University and State University at Tempe. Among Gammage's greatest achievements in Tempe was the Frank Lloyd Wright-desig
Energy conservation effort made to reduce the consumption of energy by using less of an energy service. This can be achieved either by using energy more efficiently or by reducing the amount of service used. Energy conservation is a part of the concept of eco-sufficiency. Energy conservation reduces the need for energy services and can result in increased environmental quality, national security, personal financial security and higher savings, it is at the top of the sustainable energy hierarchy. It lowers energy costs by preventing future resource depletion. Energy can be conserved by reducing wastage and losses, improving efficiency through technological upgrades and improved operation and maintenance. On a global level energy use can be reduced by the stabilisation of population growth. Energy can only be transformed from one form to other, such as heat energy to motive power in cars, or kinetic energy of water flow to electricity in hydroelectric power plants; however machines are required to transform energy from one form to other.
The wear and friction of the components of these machine while running cause loss of quadrillions of BTU and $500 billions in industries only in USA. It is possible to minimize these losses by adopting green engineering practices to improve life cycle of the components; some countries employ carbon taxes to motivate energy users to reduce their consumption. Carbon taxes can force consumption to shift to nuclear power and other energy sources that carry different sets of environmental side effects and limitations. On the other hand, taxes on all energy consumption can reduce energy use across the board while reducing a broader array of environmental consequences arising from energy production; the state of California employs a tiered energy tax whereby every consumer receives a baseline energy allowance that carries a low tax. As usage increases above that baseline, the tax increases drastically; such programs aim to protect poorer households while creating a larger tax burden for high energy consumers.
One of the primary ways to improve energy conservation in buildings is to perform an energy audit. An energy audit is an inspection and analysis of energy use and flows for energy conservation in a building, process or system with an eye toward reducing energy input without negatively affecting output; this is accomplished by trained professionals and can be part of some of the national programs discussed above. Recent development of smartphone apps enables homeowners to complete sophisticated energy audits themselves. Building technologies and smart meters can allow energy users, both commercial and residential, to visualize the impact their energy use can have in their workplace or homes. Advanced real-time energy metering can help people save energy by their actions. In passive solar building design, windows and floors are made to collect and distribute solar energy in the form of heat in the winter and reject solar heat in the summer; this is called passive solar design or climatic design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices.
The key to designing a passive solar building is to best take advantage of the local climate. Elements to be considered include window placement and glazing type, thermal insulation, thermal mass, shading. Passive solar design techniques can be applied most to new buildings, but existing buildings can be retrofitted. In the United States, suburban infrastructure evolved during an age of easy access to fossil fuels, which has led to transportation-dependent systems of living. Zoning reforms that allow greater urban density as well as designs for walking and bicycling can reduce energy consumed for transportation; the use of telecommuting by major corporations is a significant opportunity to conserve energy, as many Americans now work in service jobs that enable them to work from home instead of commuting to work each day. Consumers are poorly informed of the savings of energy efficient products. A prominent example of this is the energy savings that can be made by replacing an incandescent light bulb with a more modern alternative.
When purchasing light bulbs, many consumers opt for cheap incandescent bulbs, failing to take into account their higher energy costs and lower lifespans when compared to modern compact fluorescent and LED bulbs. Although these energy-efficient alternatives have a higher upfront cost, their long lifespan and low energy use can save consumers a considerable amount of money; the price of LED bulbs has been decreasing in the past five years due to improvements in semiconductor technology. Many LED bulbs on the market qualify for utility rebates that further reduce the price of purchase to the consumer. Estimates by the U. S. Department of Energy state that widespread adoption of LED lighting over the next 20 years could result in about $265 billion worth of savings in United States energy costs; the research one must put into conserving energy is too time consuming and costly for the average consumer when there are cheaper products and technology available using today's fossil fuels. Some governments and NGOs are attempting to reduce this complexity with ecolabels that make differences in energy efficiency easy to research while shopping.
To provide the kind of information and support people need to invest money and effort in energy conservation, it is important to understand and link to people's topical concerns. For instance, some retailers argue. However, health studies have demonstrated that headache, blood pressure and worker error all increase with the common over-illuminat
Housewrap denotes a synthetic material used to protect buildings. Housewrap functions as a weather-resistant barrier, preventing rain from getting into the wall assembly while allowing water vapor to pass to the exterior. If moisture from either direction is allowed to build up within stud or cavity walls and rot can set in and fiberglass or cellulose insulation will lose its R-value due to heat-conducting moisture. House wrap may serve as an air barrier if it is sealed at seams. Housewrap is a replacement for the older asphalt-treated paper; these materials are all lighter in weight and wider than asphalt designs, so contractors can apply the material much faster to a house shell. Asphalt-impregnated paper or fiberglass Micro-perforated, cross-lapped films Films laminated to spunbond nonwovens Films laminated or coated to polypropylene wovens Supercalendered, wetlaid polyethylene fibril nonwoven Drainable housewraps Housewrap must be both water shedding and have a high moisture vapor transmission rate to be effective.
It must take handling abuse during installation and be resistant to UV. Housewrap is left exposed for some time after construction, awaiting exterior siding installation; the original asphalt paper design, while heavy and slow to install, is still a contender. It still function; some new designs must be installed or they will rip or tear during installation allowing for water infiltration at the damaged areas. Most newer designs do not "seal" well against staples like asphalt products. Housewrap is installed behind the exterior siding. Siding can be vinyl, wood shingles or shakes, brick facade, or numerous other acceptable building materials. In all cases, the housewrap is the last line of defense in stopping incoming water or exterior water condensation from getting into the wooden stud wall. Typical MVTR ~200 grams/100 square-inches/24hours Typical 2 ounces/square-yard Typical width 90" on a 3" core
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, sleet, snow and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates", thus and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate. Two processes acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called "showers."Moisture, lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. This process is active when freezing rain occurs. A stationary front is present near the area of freezing rain and serves as the foci for forcing and rising air.
Provided necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely stratus and cumulonimbus. The cloud droplets will grow large enough to form raindrops and descend toward the Earth where they will freeze on contact with exposed objects. Where warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones. Lake-effect snowfall can be locally heavy. Thundersnow is possible within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation. On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. Most precipitation is caused by convection; the movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes.
Precipitation is a major component of the water cycle, is responsible for depositing the fresh water on the planet. 505,000 cubic kilometres of water falls as precipitation each year. Given the Earth's surface area, that means the globally averaged annual precipitation is 990 millimetres, but over land it is only 715 millimetres. Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Precipitation may occur on other celestial bodies, e.g. when it gets cold, Mars has precipitation which most takes the form of frost, rather than rain or snow. Precipitation is a major component of the water cycle, is responsible for depositing most of the fresh water on the planet. 505,000 km3 of water falls as precipitation each year, 398,000 km3 of it over the oceans. Given the Earth's surface area, that means the globally averaged annual precipitation is 990 millimetres. Mechanisms of producing precipitation include convective and orographic rainfall.
Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation, while stratiform processes involve weaker upward motions and less intense precipitation. Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice. Mixtures of different types of precipitation, including types in different categories, can fall simultaneously. Liquid forms of precipitation include drizzle. Rain or drizzle that freezes on contact within a subfreezing air mass is called "freezing rain" or "freezing drizzle". Frozen forms of precipitation include snow, ice needles, ice pellets and graupel; the dew point is the temperature to which a parcel must be cooled in order to become saturated, condenses to water. Water vapor begins to condense on condensation nuclei such as dust and salt in order to form clouds. An elevated portion of a frontal zone forces broad areas of lift, which form clouds decks such as altostratus or cirrostratus.
Stratus is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. It can form due to the lifting of advection fog during breezy conditions. There are four main mechanisms for cooling the air to its dew point: adiabatic cooling, conductive cooling, radiational cooling, evaporative cooling. Adiabatic cooling occurs when air expands; the air can rise due to convection, large-scale atmospheric motions, or a physical barrier such as a mountain. Conductive cooling occurs when the air comes into contact with a colder surface by being blown from one surface to another, for example from a liquid water surface to colder land. Radiational cooling occurs due to the emission of infrared radiation, either by the air or by the surface underneath. Evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet-bulb temperature, or until it reaches saturation; the main ways water vapor is added to the air are: wind convergence into areas of upward motion, precipitation or virga falling from above, daytime heating evaporating water from the surface of oceans, water bodies or wet lan