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Environmental recorders designed for long-term storing information regarding the air concentration of black carbon (i.e., soot). These recorders usually consist of a pump that takes a continuous stream of air from the environment; the air pass through a filtering material strip wrapped on a roll where the particles are deposited. When the density of the deposit on the filter reaches a pre-established density the roll advances to a fresh spot and the process continue. The rate at which the filter moves is proportional to the quantity of soot deposited. The recorder also includes photometric detectors to assess the filter spots; at least two frequencies should be used, usually black carbon may be detected using a near infrared wavelength (e.g., 880nm) while the presence of other organic compounds such as those found in tobacco and wood smoke (known as white carbon) may be detected using light in the ultraviolet spectrum (e.g., 370nm). Some recorders measure at more than two wavelengths (e.g., seven) to facilitate the identification and physical properties of the primary components of the soot. The recorders are mainly used to determine air quality and visibility.
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