Instruct: Given a question, retrieve passages that can help answer the question.
Query: What is the most common source of polycyclic aromatic hydrocarbons?
Polycyclic aromatic hydrocarbons (PAHs, also polyaromatic hydrocarbons or polynuclear aromatic hydrocarbons) are hydrocarbons—organic compounds containing only carbon and hydrogen—that are composed of multiple aromatic rings (organic rings in which the electrons are delocalized). The simplest such chemicals are naphthalene, having two aromatic rings, and the three-ring compounds anthracene and phenanthrene.
According to the National Resources Defense Council, cancer causing pollutants such as benzene, formaldehyde, and diesel have been found in the air near fracking sites. These pollutants generate wastewater, which is linked to groundwater contamination, threatening nearby drinking water and causing concern for anyone who is exposed. Studies done by The National Institute for Occupational Safety and Health, found that “Fracking also uses crystalline silica, which is a type of sand that’s used to keep the fractures open.” Exposure to this, along with dust and other air pollutants produced from fracking, can cause respiratory problems.
The Toxic 100 Air polluters index from the University of Massachusetts lists Precision Castparts as the number one air polluter in the U.S. in the August 2013 edition, which the company called a flawed study.
Raw natural gas consists primarily of methane (CH), the shortest and lightest hydrocarbon molecule, as well as various amounts of heavier hydrocarbon gases such as ethane (CH), propane (CH), normal butane ("n"-CH), isobutane ("i"-CH), pentanes and even higher-molecular-mass hydrocarbons. The raw gas also contains various amounts of acid gases such as carbon dioxide (CO), hydrogen sulfide (HS) and mercaptans such as methanethiol (CHSH) and ethanethiol (CHSH).
Organophosphate pesticides are one of the top causes of poisoning worldwide, with an annual incidence of poisonings among agricultural workers varying from 3-10% per country.
Air pollution, or suspended particulate matter locally generated from the increased number of automobiles in the area, from point sources such as factories, dust carried into the air by construction activity, and the contribution of similar pollutants from the Los Angeles area has regularly caused the Inland Empire to be at, or near, the bottom of many air quality ratings. In 2004, the EPA rated the San Bernardino-Riverside area as having the worst particulate air pollution in the United States (although the San Joaquin Valley in central California had the worst overall air pollution). Air pollution in the Los Angeles region is still an issue, although improvements have been made over the years. But the problem is exacerbated in the Inland Empire, which is surrounded by mountains on the north and the east. Prevailing winds move bad air eastward from Los Angeles, but once the pollution reaches the Inland Empire it cannot be carried further east as it becomes trapped by the mountains surrounding the region .
Mobile source air pollution includes any air pollution emitted by motor vehicles, airplanes, locomotives, and other engines and equipment that can be moved from one location to another. Many of these pollutants contribute to environmental degradation and have negative effects on human health. To prevent unnecessary damage to human health and the environment, environmental regulatory agencies such as the U.S. Environmental Protection Agency have established policies to minimize air pollution from mobile sources. Similar agencies exist at the state level. Due to the large number of mobile sources of air pollution, and their ability to move from one location to another, mobile sources are regulated differently from stationary sources, such as power plants. Instead of monitoring individual emitters, such as an individual vehicle, mobile sources are often regulated more broadly through design and fuel standards. Examples of this include corporate average fuel economy standards and laws that ban leaded gasoline in the United States. The increase in the number of motor vehicles driven in the U.S. has made efforts to limit mobile source pollution challenging. As a result, there have been a number of different regulatory instruments implemented to reach the desired emissions goals.
Pollution in California relates to the degree of pollution in the air, water, and land of the state of California. Pollution is defined as the addition of any substance (solid, liquid, or gas) or any form of energy (such as heat, sound, or radioactivity) to the environment at a faster rate than it can be dispersed, diluted, decomposed, recycled, or stored in some harmless form. The combination of three main factors are the cause of notable unhealthy levels of air pollution in California: the activities of over 39 million people, a mountainous terrain that traps pollution, and a warm climate that helps form ozone and other pollutants. Eight of the ten cities in the US with the highest year-round concentration of particulate matter between 2013 and 2015 were in California, and seven out of the ten cities in the US with the worst ozone pollution were also in California. Studies show that pollutants prevalent in California are linked to several health issues, including asthma, lung cancer, birth complications, and premature death. In 2016, Bakersfield, California recorded the highest level of airborne pollutants of any city in the United States.
People have been using natural organic polymers for centuries in the form of waxes and shellac, which is classified as a thermoplastic polymer. A plant polymer named cellulose provided the tensile strength for natural fibers and ropes, and by the early 19th century natural rubber was in widespread use. Polymers are the raw materials (the resins) used to make what are commonly called plastics. Plastics are the final product, created after one or more polymers or additives have been added to a resin during processing, which is then shaped into a final form. Polymers that have been around, and that are in current widespread use, include carbon-based polyethylene, polypropylene, polyvinyl chloride, polystyrene, nylons, polyesters, acrylics, polyurethane, and polycarbonates, and silicon-based silicones. Plastics are generally classified as "commodity", "specialty" and "engineering" plastics.
In October 2014, Houston-based oil field services company Baker Hughes was reported to have produced 1,000 pink drill bits to raise breast cancer awareness. The land drill bits are used to break up geologic formations in oil patches for hydraulic fracturing. These ties have been criticized, because of the more than 700 chemicals used in fracking more than one third are endocrine disruptors and at least one quarter increase the risk of cancer.
People of lower socioeconomic status are found to be more vulnerable to air pollutant, PM 2.5, due to their location. PM 2.5 is an air pollutant, arising from the blend of power plants, refineries, and diesel engines, among other sources, and this particle penetrates the lungs. Communities of low socioeconomic statuses are frequently concentrated in areas near highways, busy roads, and refineries. Therefore, limiting one's exposure to air pollution in an impoverished environment is nearly impossible. Communities of low socioeconomic status face an unequal access to environmental health services and resources.
Some familiar household synthetic polymers include: Nylons in textiles and fabrics, Teflon in non-stick pans, Bakelite for electrical switches, polyvinyl chloride (PVC) in pipes, etc. The common PET bottles are made of a synthetic polymer, polyethylene terephthalate. The plastic kits and covers are mostly made of synthetic polymers like polythene and tires are manufactured from Buna rubbers. However, due to the environmental issues created by these synthetic polymers which are mostly non-biodegradable and often synthesized from petroleum, alternatives like bioplastics are also being considered. They are however expensive when compared to the synthetic polymers.The eight most common types of synthetic organic polymers, which are commonly found in households are:
The Air pollution is the release of chemicals and particulates into the atmosphere. Common gaseous pollutants include carbon monoxide, sulfur dioxide, chlorofluorocarbons (CFCs) and nitrogen oxides produced by industry and motor vehicles. Photochemical ozone and smog are created as nitrogen oxides and hydrocarbons react to sunlight. Particulate matter, or fine dust is characterized by their micrometre size PM to PM. The air in Karachi is rapidly polluted by automobile smoke, especially Rickshaws and Buses, industrial emissions, open burning of garbage, house fires, and other particles but the government and environment organizations seems non-serious to tackle the issue timely.
The two-stroke engines on rickshaws and motorcycles are one of the major polluters of air in Karachi and the rest of Pakistan. The two-stroke engines as well as defective or unturned vehicles are major polluters with carbon dioxide emissions. Two-stroke engines as well as defective vehicles using substandard lubricant are major emitters of sulfur dioxide and smoke. Automobiles operating on compressed natural gas and liquefied petroleum gas are major air polluters.
Although Los Angeles remains the city with the worst ozone pollution, the state of air pollution has been improving. With a population of roughly over 10 million, the Los Angeles area is a large basin with the Pacific Ocean to the west, and several mountain ranges with 11,000-foot peaks to the east and south, Los Angeles is particularly susceptible to high ozone levels. Diesel engines, ports, motor vehicles, and industries are main sources of air pollution in Los Angeles. Frequent sunny days and low rainfall contribute to ozone formation, as well as high levels of fine particles and dust. The strong relationship between Air Quality Index (AQI) and ozone levels may be found on air pollution maps.
Organophosphate is the general name for esters of phosphoric acid and is one of the organophosphorus compounds. They can be found as part of insecticides, herbicides, and nerve gases, amongst others. Some less-toxic organophosphates can be used as solvents, plasticizers, and EP additives. The use of organophosphates accounts for approximately 38% of all pesticide use globally.
Between April 2000 and April 2001, the APCD, the U.S. Environmental Protection Agency, the Kentucky Division for Air Quality, and the University of Louisville worked with the WJCCTF to conduct an air monitoring study of a large number of toxic air pollutants at twelve sites in western Louisville and Jefferson County. The purpose of the study was to determine if residents of the area were being exposed to airborne concentrations of toxic air pollutants that may pose unacceptable risks to human health. Since the end of that one-year study, the university and WJCCTF have continued to sample volatile organic compounds at some of the sites.
The Arctic region is one of the many natural sources of the greenhouse gas methane. Global warming accelerates its release, due to both release of methane from existing stores, and from methanogenesis in rotting biomass. Large quantities of methane are stored in the Arctic in natural gas deposits, permafrost, and as undersea clathrates. Permafrost and clathrates degrade on warming, thus large releases of methane from these sources may arise as a result of global warming. Other sources of methane include submarine taliks, river transport, ice complex retreat, submarine permafrost and decaying gas hydrate deposits.
Catalytic combustion is a chemical process which uses a catalyst to speed desired oxidation reactions of a fuel and so reduce the formation of undesired products, especially pollutant nitrogen oxide gases (NO) far below what can be achieved without catalysts. The process was discovered in the 1970s at Engelhard Corp.
Natural biodegradable polymers are formed in nature during growth cycles of all organisms. When searching for natural fibers to replace synthetic materials in athletic shoes, the major natural biodegradable polymer that offers the most potential are polysaccharides. Starch is a polysaccharide that is useful because it readily degrades into harmless products when placed in contact with soil microorganisms.
Methane was discovered and isolated by Alessandro Volta between 1776 and 1778 when studying marsh gas from Lake Maggiore. It is the major component of natural gas, about 87% by volume. The major source of methane is extraction from geological deposits known as natural gas fields, with coal seam gas extraction becoming a major source (see Coal bed methane extraction, a method for extracting methane from a coal deposit, while enhanced coal bed methane recovery is a method of recovering methane from non-mineable coal seams). It is associated with other hydrocarbon fuels, and sometimes accompanied by helium and nitrogen. Methane is produced at shallow levels (low pressure) by anaerobic decay of organic matter and reworked methane from deep under the Earth's surface. In general, the sediments that generate natural gas are buried deeper and at higher temperatures than those that contain oil.
By 1964, the department had developed an AQI called the SCS Air Pollution Index (SCS API), combining measurements of sulfur dioxide (SO), carbon monoxide (CO), and coefficient of haze (also called smoke shade) into a single number. The city laboratory recorded the presence of those three pollutants measured in amount (by concentration in the air) and duration. SO and CO were measured by parts-per-million, or ppm, and smoke shade was measured in mppcf (millions of particles per cubic foot); the department continuously monitored these pollutant levels and recorded their hourly averages. The data for those three pollutants were combined into a single number using a weighted formula developed by department co-founder Moe Mordecai Braverman. The SCS API formula was:
Chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) are a group of compounds comprising polycyclic aromatic hydrocarbons with two or more aromatic rings and one or more chlorine atoms attached to the ring system. Cl-PAHs can be divided into two groups: chloro-substituted PAHs, which have one or more hydrogen atoms substituted by a chlorine atom, and chloro-added Cl-PAHs, which have two or more chlorine atoms added to the molecule. They are products of incomplete combustion of organic materials. They have many congeners, and the occurrences and toxicities of the congeners differ. Cl-PAHs are hydrophobic compounds and their persistence within ecosystems is due to their low water solubility. They are structurally similar to other halogenated hydrocarbons such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). Cl-PAHs in the environment are strongly susceptible to the effects of gas/particle partitioning, seasonal sources, and climatic conditions.
PAHs with five or six-membered rings are most common. Those composed only of six-membered rings are called "alternant" PAHs, which include "benzenoid" PAHs. The following are examples of PAHs that vary in the number and arrangement of their rings:
Polycyclic aromatic hydrocarbons (PAH) are the most common and abundant of the known polyatomic molecules in the observable universe, and are considered a likely constituent of the primordial sea. In 2010, PAHs, along with fullerenes (or "buckyballs"), have been detected in nebulae.
Priority polycyclic aromatic hydrocarbons identified by the US EPA, the US Agency for Toxic Substances and Disease Registry (ATSDR), and the European Food Safety Authority (EFSA) due to their carcinogenicity or genotoxicity and/or ability to be monitored are the following: