Search toxic substances by Chemical Abstracts Service Number (CAS#), substance name, synonym, or tradename.
Agency for Toxic Substances and Disease Registry's
Earth's atmospheric airLast Updated on 2014-04-02 14:56:48The Earth's atmospheric air is a colorless, odorless and tasteless mixture of gases consisting mostly of nitrogen (N2) and oxygen (O2). It is the part of Earth's atmosphere that humans and all other animals breathe in order to obtain the oxygen needed to sustain life.
The Earth's atmosphere not only contains the air we breathe, it also holds clouds of moisture (water vapor) that become the water we drink. Furthermore, it protects us from meteors and harmful solar radiation and warms the Earth's surface by heat retention. In effect, the atmosphere is an envelope that protects all life on Earth.
The air may contain pollutants that originate from a variety of sources such as our industries and our vehicles, and can directly or indirectly affect our health and the natural environment. These effects may be experienced near the sources of air pollution and some air... More »
RespirationLast Updated on 2014-01-31 16:43:42Respiration is the gas exchange effected by living organisms for the purpose of sustaining vital metabolic processes. In the case of most animals, oxygen is taken into the organism, and carbon dioxide is expelled. In the case of plants, the inverse process occurs of consuming carbon dioxide and expelling oxygen as a waste gas.
Respiration may also be viewed at a cellular level, examining gas exchange at the cell wall; for very simple organisms, such as unicellular lifeforms, the process of gas exchange with the environment is simplified, so that cellular wall gas exchange is the totality of respiration for such an organism.
In the case of some bacteria and archaea, respiration sometimes occurs without any oxygen, and alternative molecular gases such as hydrogen sulfide or methane may participate in respiration and subsequent cellular metabolic reactions. Often such organisms are... More »
Carbon monoxideLast Updated on 2014-01-16 09:44:12Carbon monoxide (CO), also referred to as carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. Exposure to high levels of carbon monoxide is extremely toxic to humans and animals. Conversely, small amounts of carbon monoxide are produced in normal animal metabolism and it is thought to have some normal biological functions.
Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest member of the class of inorganic compounds known as oxocarbons which includes carbon dioxide (CO2), carbon suboxide (C3O2), mellitic anhydride (C12O9) and many others. When combined with a metal (i.e. an organometallic complex), the carbon monoxide is a ligand called carbonyl: for example, in nickel carbonyl with the formula Ni(CO)4.
Carbon monoxide is produced by the partial combustion of carbon-containing substances. It is produced... More »
CalciumLast Updated on 2013-10-24 16:29:12Calcium is the chemical element with atomic number 20; it has an atomic mass of 40.078 atomic mass units (amu). The chemical symbol for calcium is Ca. Calcium is a soft gray alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust; moreover, it is the fifth most abundant dissolved ion in seawater both in terms of number of atoms and mass, after sodium, chloride, magnesium, and sulfate.
Calcium an is essential nutrient for almost all living organisms, with vital roles in cellular metabolism, especially with regard to movement of the calcium ion Ca++ into and out of the cytoplasm functions as a signal for many cellular processes. As a chief component needed in mineralization of bones and shells, calcium is the most abundant metal by mass in a large number of faunal species, especially vertebrates, testudines and mollusca.
Previous... More »
AERMOD Last Updated on 2013-10-05 15:00:30AERMOD is the latest generation air dispersion model designed for short-range (up to 50 kilometers) dispersion of air pollutant emissions from stationary industrial sources. It is a steady-state plume model incorporating dispersion based on planetary boundary layer (PBL) turbulence structure and scaling, and it accomodates surface and elevated emission sources as well as simple or complex terrain.
As of December 9, 2005, the U.S. EPA designated AERMOD as the preferred model to be used for compliance with any federal and state air pollution dispersion modeling requirements. As of November 9, 2006, AERMOD completely replaces the previous preferred model known as the Industrial Source Complex (ISC) model.
The AERMOD system integrates three modules:
A steady-state Gaussian dispersion model designed for short-range dispersion of continuous emissions from stationary... More »
Drag and drop the content to change the order of featured content. The top nine will be displayed.