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In those cases where usual or highly toxic known air contaminants are known to be present at <br /> a hazardous waste site, assistance should be requested from the Health and Safety program manager <br /> (HSPM) to determine the most appropriate method of air sampling for those contaminants <br /> ' 4.1 ULTRAVIOLET PHOTOIONIZATION DETECTOR <br /> ' A photoionization detector detects total concentration of many organic and some inorganic <br /> gases and vapors Some identification of compounds is possible if more than one probe is used <br /> 4.1.1 Theory <br /> When passed through a prism, the light from the sun disperses into the many colors that make <br /> ' up the whole light spectrum The hues of colors from the deep reds through the deep purples are a <br /> relatively small segment in the overall electromagnetic (e-m) spectrum <br /> ' The e-rn spectrum covers long wavelengths such as radio waves through the ultra-shortwave <br /> gamma radiation As the wavelengths decrease in size (higher frequencies), the wave energy <br /> increases This relationship between energy and frequency is based upon Planck's equation <br /> 1 All atoms and molecules are composed of particles electrons, protons, and neutrons <br /> ' Electrons are negatively charged particles that rotate in orbit around the nucleus, the dense inner core <br /> The nucleus consists of an equal number of protons (positively charged particles) as electrons found in <br /> the orbital cloud The interaction of the oppositely charged particles and the laws of quantum <br /> ' mechanics keep the electrons in orbits outside the nucleus <br /> ' The energy required to remove the outermost electron from the molecule is called the <br /> ionization potential (IP) and is specific for any chemical compound or atomic species IP is measured <br /> ' in electron volts (eV) High frequency radiation (ultraviolet and above) is capable of causing <br /> ionization and is hence called ionizing radiation <br /> When a photon of UV radiation strikes a chemical compound, it ionizes the molecule if the <br /> ' energy of the radiation is equal to or greater than the IP of the compound Since ions are capable of <br /> O - 7 <br />