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GLOSSARY Actinic or solar degeneration: A complex of degenerative changes in skin caused by chronic exposure to sunlight. The skin appears thick and furrowed but may also have zones of thinned epidermis. Action spectrum: A graph or mathematical expression indicating the relative effectiveness of radiation at different wavelengths for producing a photochemical or photobiological effect. Antigen: Any substance that, when introduced into,the body, stimulates the production of an antibody, a protein that acts to neutralize the antigen and thus produce immunity. Backscatter ultraviolet (B W): Solar radiation in the ultraviolet region that is scattered from the atmosphere back into space. Basal cell skin cancer: A relatively common type of skin cancer that can result from exposure to sunlight. Its tendency to metastasize is small. This cancer arises in the basal cell layer of the epidermis where cells continually divide and replace dead cells in the epidermis. Carcinogenesis: The production and development of cancer. The process of carcinogenesis may be divided into at least two parts. The first part, initiation, involves the interaction of a physical or chemical carcinogen with cells, resulting in altered cells that are potentially cancerous, or precancerous. Such an altered cell may remain quiescent for a long time before subsequent cell proliferation and the expression of a tumor. The second part, promotion, involves the subsequent proliferation of the altered cells. Substances called promoters, administered after, even long after, the initiating event, may 134
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135 result in observed tumors. But, if administered before the initiating event, promoters will not enhance the observed carcinogenic effects of initiators. Initiators are thought to act via reactions with cellular macromolecules--in many instances DNA. The molecular mechanisms of promotion are not well understood, but are hypothesized to affect the regulatory activities of cells or cell-cell interactions (Berenblum and Armuth 1981). Catalysis: A means by which the rate of a chemical reaction is enhanced through the action of a catalyst (a substance that itself remains chemically unaltered). Catalytic cycle: A set of chemical reactions wherein one or more reactive species are alternately consumed and generated. The net effect is to cause a reaction between the partners of the reactive species to yield the products. The simplest example of a catalytic cycle involving ozone is O3 + NO + NO2 ~ O2 O + NO2 ~ NO + O2 O3 + 0 ~ O2 + O2 (net). _ In these reactions the molecules NO and NO2 act as catalysts for the combination of O-atoms with O3 to produce O2. The direct reaction can occur, but the presence of NO and NO2 (causing the same net change) increases the rate by means of the two-reaction pathway. ~. Chlorocarbon: A hydrocarbon in which one or more chlorine atoms are substituted for hydrogen atoms. Chlorofluorocarbon: A hydrocarbon containing chlorine and fluorine as substituents for hydrogen atoms. Chlorofluoromethane: A methane derivative containing chlorine and fluorine as substituents. Chromatin: A complex of highly polymerized DNA with basic proteins (histone or protamine) that stains intensely with basic dyes; regarded as the physical carrier of genes. Chromophores: Molecules or parts of molecules that absorb light. Cohort: A group born in a specific time interval, e.g., one calendar year. Cohort analysis: The study of a cohort from its inception to its final dissolution, e.g., a study of
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136 all the people born in one calendar year followed until the last person dies. Contact hypersensitivity: An immune system response at the cellular level to an antigen applied to the skin, to which the animal has been previously sensitized. The response is specific to the antigen due to specific cell-surface antigen receptors. Core regions of chromatin: Mammalian DNA may be visualized as a strand with aggregates of protein occurring at intervals along the strand. The protein aggregates are called nucleosomes, and are known as core regions, and the intervening areas are the linker regions . Cross-sectional analysis: A type of empirical analysis, i.e., analysis concerned with the establishment of quantitative or qualitative relations between observable variables, using cross-section data. Cross-section data are observations on variables at a point in time, as opposed to time-series data. Dermis: A 1-mm to 4-mm layer of primarily collagenous connective tissue that provides much of the structural integrity of the skin. It is located beneath the epidermis. Ecosystem: A dynamic, integrated assemblage of plants, animals, and microorganisms that is definable by the interactions among the living and nonliving components of the functional unit. Eddy diffusion: A process whereby, through the action of random eddies in a turbulent fluid, heat and/or matter is transported along a gradient. Epidermis: The outermost layer of the skin, approximately 100 am thick, separated from the next layer (dermis) by a basement membrane. The epidermis consists of five layers: (1) the outermost protective stratum corneum (no nuclei); (2) several layers of transparent nucleated cells; t3) the granular layer, (4) the Malpighian layer, consisting of multiple squamous or prickle cells; and (5) the basal layer, composed of germinative cells. Less than 10 percent of incident W-B may pass through the epidermis. Erythema: A reddening of the skin due to a dilation of the blood capillaries. It is one of the components of the syndrome commonly known as sunburn. Excision repair: A cellular repair mechanism that eliminates photoproducts in DNA, thereby ameliorating UV damage to DNA. In this process, products of UV irradiation are removed from one strand of a DNA
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137 double helix by specific enzymes that work in the dark. The opposite unaltered strand is then used as a template on which a new complementary strand is built. Fibroblast: A connective tissue cell, flat and elongated. It performs the function of supporting and binding tissues of all sorts in higher organisms. Freon: The U.S. trade name for several chlorofluorocarbons. Fell, F-12: The halocarbon Fell is trichloro- fluoromethane CFC13 and F-12 is dichlorodi- fluoromethane CF2C12. These are the two most-used chlorofluorocarbons and they constitute most of the threat to ozone by this class of compounds. Halocarbon: A hydrocarbon in which one or more halogen atoms are substituted for hydrogen atoms. Heterochromatic light or radiation: Light or radiation consisting of a range of (more than a single) wavelengths. See also monochromatic light or radiation. Hydrocarbon: A compound of hydrogen and carbon. Immunosuppression: The suppression of a natural immune response of an organism to a foreign agent. Initiator. See carcinogenesis. Langerhans cells: In the skin, dendritic cells in the epidermis that function as part of the immune system. Lentigo malignant melanoma: A subtype of melanoma occurring almost exclusively on the exposed parts of the face, neck, and hands; characterized by the presence of brownish pigmented spots on the skin (lentigines or freckles) that increase in size and darken in color. The spots are predominantly flat, 2 cm to 20 cm in diameter with irregular borders and pigment pattern. Raised areas indicate invasive tumor. Linker regions of chromatic: See core regions of chromatic. Lymphocytes: Circulating white blood cells that are part of the immune system. Mast cell: A connective tissue cell whose physiologic function remains partly unknown; after a variety of insults or stimuli the cell releases chemicals that are mediators of inflammation. Melanin: A dark pigment found in skin (epidermis), hair, and various tumors. The epidermal melanin unit is composed of melanocytes and associated Malpighian cells. See also epidermis, melanocytes. Melanocytes: Cells located in the basal layer of the epidermis with dendritic (armlike) projections that
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138 extend into the Malpighian layer of the epidermis. These cells form the pigment melanin, which they pass into the Malpighian cells. Melanoma: A tumor made up of melanin-pigmented cells. Melanoma is a serious, sometimes fatal form of skin cancer, usually developing from a nevus and consisting of black masses of cells with a tendency to metastasize. Mixing ratio: The ratio of the concentration of a gaseous species to the total concentration of the gas. Model: In the context of Part I of this report a model is a mathematical representation of the transport and chemical behavior of species in the atmosphere. In principle, with suitable specification of initial and boundary conditions, the distributions of any and all (relevant) chemical species in space and time can be computed by means of the model. Monochromatic light or radiation: Light or radiation consisting of a single wavelength. See also heterochromatic light or radiation. Nevus: Any congenital growth or mark on the skin, such as a birthmark. Odd-hydrogen compound: Specifically one of the radical species OH (hydroxyl) and HO2 (hydroperoxyl) that contain a single H-atom each. The term odd-hydrogen is used more in analogy with odd-nitrogen and odd oxygen (see below). Odd-nitrogen compound: One of the species containing a single nitrogen atom such as NO, NO2, HNO3, ClONO 2, MONO, and HOONO 2 . Odd-oxygen species: Specifically O-atoms and O3 (as opposed to the "even oxygen" species O2). Since O-atoms are rapidly converted mainly to O3, reactions which remove them are considered as effectively removing O3. The set of reactions that remove both odd-oxygen species thus constitutes the means by which ozone abundance becomes reduced. Ozone (O3): An allotrope of oxygen containing three atoms. It is a reactive, toxic, acrid smelling, colorless gas under atmospheric conditions. It is created naturally in the stratosphere where its abundance is the largest and where it exists as a permanent layer. Ozone is created in the troposphere by the so-called smog reactions involving the oxides of nitrogen and hydrocarbons. Ozonesonde: (a) One of several devices that are carried aloft through the atmosphere by balloons to measure
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139 the vertical concentration distribution of ozone. (b) The plotted record of the vertical concentration distribution of ozone obtained by such a device. Photochemical reaction: Any reaction in which one or more of the reactants or their reactive precursors are created by the interaction of light with a molecule or atom. Generally the term refers to free radical reactions wherein the radicals or their radical precursors were created by photolysis of a stable molecule. Photobiology: That branch of biology that deals with the effects of light on living organisms. Photochemistry: That branch of chemistry that deals with the chemical effects of light. Photoimmunology: That branch of immunology that deals with the effects of light on the immune system. Most of what is now known about the effects of W on the immune systems of animals and humans has been learned within the past five years. Photokeratitis: An acute, painful irritation of the cornea of the eye caused by exposure to UV-B or WV-C. Photon: A "particle" of light. A photon is the smallest unit (quantum) of light that exists; its energy depends on the wavelength of the light. Photoproducts: Specific changes in molecular structure that result from the absorption by molecules of photons (in this report, photons in the W band specifically). Photoprotection: A protective cellular mechanism whereby a preceding illumination with W-A may decrease the damage to DNA caused by UV-B. Photoprotection involves the induction by W-A of a delay in growth, allowing for more time after UV-B irradiation is completed for error-free dark-repair systems to repair the damaged DNA. Photoreactivation: A cellular repair mechanism that eliminates photoproducts in DNA, thereby ameliorating UV damage to DNA. In this process, an enzyme binds to a DNA molecule containing pyrimidine dimers. The complex of enzyme and damaged DNA can absorb W-A or visible light, which causes the dimer to split, thereby repairing the damage. Planetary waves: Longitudinally ranging motions of the atmosphere organized on a scale of the magnitude of the distance around the earth. Promoter: See carcinogenesis.
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140 Pyrimidine dimers: Biologically damaging products of UV irradiation, formed when two adjacent pyrimidine residues within one DNA strand bond to each other. Radical (also called free radical): Any chemical species (atom or molecule or ion) that contains one or more unpaired electrons. In this report the term refers to reactive species such as OH, HO2, C1, and C1O, each of which contains a single unpaired electron. The ease of combining with other molecules to form bonds having paired electron spins is understood as the seat of their reactivity. Rate-limiting reaction (or process): In a sequence of reactions, that reaction which is the slowest and thus limits the rate at which the initial reactants ultimately become converted to products. Robertson-Berger (R-B) meter: A meter that records, after each 30-minute interval, a measure of the cumulative amount of UV that passes through its filters and is absorbed by its photosensors. Half-hourly recordings may range from 0 to slightly over 1000 depending on geographical location and prevailing meteorological conditions. The meters are designed to measure UV effective in producing skin erythema (sunburn), but in fact measure some longer UV wavelengths as well (see Figure 2.2). A count of about 400 in a half hour is estimated to produce skin erythema on the typical Caucasian skin. Solar backscatter UV (SB W): See backscatter ultraviolet. Solar degeneration: See actinic or solar degeneration. Spectrophotometer: An electro-optical device that measures the intensity of light distributed over a spectral range (of wavelength or frequency). The Dobson meter is an example of a specialized spectrophotometer that measures and intercompares the relative intensities of sunlight at four different wavelengths, two of which correspond to absorption peaks in the ozone spectrum. From this measurement, the column abundance of ozone can be calculated. Squamous cell skin cancer: A relatively common type of skin cancer that can result from exposure to sunlight. Its tendency to metastasize is small. This cancer arises in the Malpighian layer of the epidermis Stratosphere: The region of the atmosphere above the tropopause (altitude range 6 km to 17 km) and below the stratopause (altitude about 55 km). The principal characterizing feature of the stratosphere is its .
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141 thermal stability. That is, the temperature increases with increasing height in the stratosphere. Stratum corneum: A low m layer of dead cells, protein, and other molecules on the outermost surface of the epidermis. W-B is strongly absorbed by the stratum corneum. T suppressor cells: suppresses cellular immune response. Transformation (in vitro): An inheritable change wherein cells in culture are altered such that they do not stop growing when they encounter similar cells. Colonies of UV-transformed rodent cells are often tumorigenic when injected into certain animals, but no tumorigenicity has been shown for the W-transformed human cells described in the experimental results shown in Figure 3.1. Tropopause: The surface that is the boundary between the troposphere and the stratosphere. The height of this surface varies in the range 6 km to 17 km depending upon latitude and season. Troposphere: The main layer of the atmosphere between the surface and the tropopause. Ultraviolet radiation (W): Light in the range of wavelengths less than 400 nm. The lower limit is a matter of definition to distinguish between W and x-rays at even shorter wavelengths. Ultraviolet radiation in the wavelength region from 320 nm to 400 nm; near- W . UV-B: Ultraviolet radiation in the wavelength region from 290 nm to 320 nm; mid-UV. WV-C: Ultraviolet radiation in the wavelength region from 190 nm to 290 nm; far- W. Umkehr method: A mathematical manipulation of the data from the Dobson spectrophotometer that creates a rough representation of the vertical profile of ozone. The data come from measurements of the zenith sky as the A certain class of lymphocytes that WV-A: sun rises or sets. Xeroderma pigmentosum: A genetically inherited, sunlight-sensitive, cancer-prone disease; rare and often fatal if the individuals are not protected from sun exposure; characterized by brown spots and ulcers of the skin. Cells from individuals with this disease are almost always defective in DNA repair, and the high prevalence of skin cancer in such individuals is ascribed to this defect.
Representative terms from entire chapter: