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عنوان فارسی مقاله:
یک LED دوگانه جدید مبتنی بر ابزار دیفرانسیل طیف سنجی جذب نوری برای اندازه گیری هیدروکربن های آروماتیک
عنوان انگلیسی مقاله:
A novel dual-LED based long-path DOAS instrument for the measurement of aromatic hydrocarbons
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Long Path Differential Optical Absorption Spectroscopy (LPDOAS) is a powerful method for identifying and quantifying pollutants in the UV/visible spectral region using their unique narrow-band absorption features (Platt and Stutz, 2008). LP-DOAS has been a staple of atmospheric chemistry research for several decades, but its implementation for air quality monitoring has been slow, and only moderately successful. The most common use of LPDOAS has been the monitoring of pollutants such as O3, SO2, and NO2, as well as research of the chemistry of HCHO, HONO, NO3, halogen oxides, glyoxal, and other short-lived reactive species (Platt and Stutz, 2008).Another class of compounds that can be measured by LP-DOAS is aromatic hydrocarbons, such as benzene, toluene, xylenes (BTX), etc. (Axelsson et al., 1995; Barrefors, 1996; Skov, 2001; Trost et al., 1997; Volkamer et al., 1998; Wideqvist et al., 2003). Aromatic hydrocarbons are known for their various detrimental health effects (Snyder et al., 1993; Weisel, 2010). Benzene is a known carcinogen for which the US EPA and WHO do not define a safe lower limit of exposure (http://www.epa.gov/airtoxics/hlthef/ benzene.html, http://www.who.int/ipcs/assessment/public_ health/benzene/en/), while the evidence for carcinogenicity is inconclusive for toluene and xylenes (http://www.epa.gov/ airtoxics/hlthef/toluene.html, http://www.epa.gov/airtoxics/ hlthef/xylenes.html). Aromatics also contribute to the formation of secondary pollutants such as ozone and particles in urban areas (Finlayson-Pitts and Pitts, 1999). Sources of aromatics include vehicles, solvent use, and the petrochemical industry. The latter has received considerable attention due to high BTX levels in neighborhoods adjacent to petrochemical facilities, and recent accidents leading to enhanced releases of these compounds. The US EPA recently adopted a rule on “Petroleum Refinery Sector Risk and Technology Review and New Source Performance Standards” (http://www.epa.gov/airtoxics/petref.html), which, for the first time, defines a requirement for refineries to monitor fence-line benzene concentrations, and establishes a 2-week averaged benzene concentration action level of ~3 ppb. Consequently, there has been a push to better monitor the release of BTX from petrochemical facilities on long time scales. In addition, there is a need for a rapid alarm system to warn neighbors of accidental releases. LP-DOAS offers a unique opportunity to address these current needs, and it is thus somewhat surprising that it has not found more widespread use as a fence-line and neighborhood-scale monitor for aromatic hydrocarbons. This may be, in part, due to the lack of reliable, easy-to-use LP-DOAS instruments to measure aromatics, as well as a number of difficulties in the application of LP-DOAS for these observations. DOAS is a well-established method to measure path-integrated trace gas absorptions and concentrations in the open atmosphere (Platt and Stutz, 2008). The basis of DOAS is the identification and quantification of narrow-band absorptions in the UVevis wavelength range along an open absorption path in the atmosphere using the Beer-Lambert law and wellknown trace gas absorption cross sections. The measurement in the open atmosphere, together with the fact that the absorption cross sections are intrinsic physical properties, makes DOAS an absolute analytical technique that does not require calibration. LP-DOAS instruments typically consist of a light source, a telescope and reflector (monostatic setup) or sending and receiving telescopes (bistatic setup) that define the atmospheric absorption paths, and a spectrometer/detector combination to record the absorption spectra.
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