Polycyclic aromatic hydrocarbons pahs the name

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polycyclic aromatic hydrocarbons (PAHs);the name describes their structure of multiple carbon rings fused together. PAHs, which are present in petroleum and are also a product of incomplete combustion, are ubiquitous in the environment. Once the eleŵeŶtal ŵerĐurLJ reaĐhes the Earth’s surfaĐe, ĐertaiŶ speĐies of ďaĐteria ĐoŶǀert the mercury from its elemental form to a different form: an organic compound called methylmercuryMethylmercury is taken up by algae, the first link in an aquatic food chain that leads through zooplankton, small invertebrates, and fish of increasing size lead has long been known to be neurotoxic at high doses. However, in contrast to mercury, which occurs naturally in coal, lead was deliberately added to gasoline to improve engine performance oil contains some naturally occurring volatile organic compounds (VOCs)organic compounds, such as benzene, that volatilize significantly at ordinary environmental temperature released when oil is burned photochemical smogis created through a complex series of chemical reactions among NOX, VOCs, and other chemicals in the presence of sunlight. chemicals transformed in the environment, produce secondary pollutants ozone in the stratosphere is valued for the protection it provides against ultraviolet radiation. smog, originally coined as a combination of smoke and fog, is sometimes used more generally to refer to any visible air pollutionThese secondary pollutants are then deposited in precipitationan outcome originally dubbed acid rain and now known more formally as acid deposition At thelarynx, the throat gives way to the cartilaginous trachea (windpipe), which is considered a part of the lower respiratory systemBelow thetrachea, the air passages become more and more finely subdivided. The trachea divides into two bronchi (singular bronchus), which are also cartilaginous airways, surrounded by muscles, each serving one lung.Gas exchange, the real business of breathing, takes place deeper in the lung. Bronchioles divide into respiratory bronchiolesvery small conducting airways that are a sort of transitional zonewhich in turn become alveolar ductsfind more resources at oneclass.comfind more resources at oneclass.com
Chapter 4 JAN 15 The walls of the alveolar ducts have many outpocketings: clusters of tiny sacs called alveoliA network of capillaries twines around the alveoli, enabling the exchange of gases: diffusion of oxygen from alveoli to bloodstream, and diffusion of carbon dioxide in the reverse direction. The total alveolar surface area in contact with capillaries is approximately 75 square meters, roughly the area of a tennis court As a general rule, particulates 10 microns or less in diameter are consideredrespirable particulates.Particulates from 2.5 to 10 microns come mainly from natural or mechanical sources (such as plowing, grinding, or abrasion), whereas fine particulates (PM2.5) come mostly from combustion Ultrafine particulatesare those 0.1 microns or less in diameter

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