Editing Report on integration across networks: common strategy and common sensors for lidar and aerosol extinction measurements
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The CAPS technique, similar in its basic principle to cavity ring-down, relies on the use of a short (26 cm) sample cell employing high reflectivity mirrors (Kebabian and Freedman, 2007; Kebabian et al., 2007). Square-wave modulated light emitted from a light emitting diode (LED) is directed through one mirror into the sample cell (see Figure 3).The distortion in the square wave caused by the effective optical path length within the cavity (approx. 2 km light path) is measured as a phase shift in the signal and is detected by a vacuum photodiode which is located behind the second mirror. The signal is generated in the instrument via light extinction by particles (CAPS PMex) or light absorption by NO<sub>2</sub> molecules (CAPS NO<sub>2</sub>). A detailed description of the method including first results from laboratory characterization and field deployment is given by Massoli et al. (2010), while Yu et al. (2011) reports an application to the direct measurement of combustion particle emissions from aircraft engines. The IAGOS Instrument P2e combines CAPS PMex and CAPS NO<sub>2</sub> detectors. | The CAPS technique, similar in its basic principle to cavity ring-down, relies on the use of a short (26 cm) sample cell employing high reflectivity mirrors (Kebabian and Freedman, 2007; Kebabian et al., 2007). Square-wave modulated light emitted from a light emitting diode (LED) is directed through one mirror into the sample cell (see Figure 3).The distortion in the square wave caused by the effective optical path length within the cavity (approx. 2 km light path) is measured as a phase shift in the signal and is detected by a vacuum photodiode which is located behind the second mirror. The signal is generated in the instrument via light extinction by particles (CAPS PMex) or light absorption by NO<sub>2</sub> molecules (CAPS NO<sub>2</sub>). A detailed description of the method including first results from laboratory characterization and field deployment is given by Massoli et al. (2010), while Yu et al. (2011) reports an application to the direct measurement of combustion particle emissions from aircraft engines. The IAGOS Instrument P2e combines CAPS PMex and CAPS NO<sub>2</sub> detectors. | ||
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− | + | Figure 3: Left: operation principles and key components of the CAPS method (LED wavelength 630 nm for CAPS PM<sub>EX</sub> and 450 nm for CAPS NO<sub>2</sub>); Right: schematic of the signal generation in a CAPS instrument. | |
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− | Figure 3: Left: operation principles and key components of the CAPS method (LED wavelength 630 nm for CAPS PM<sub>EX</sub> and 450 nm for CAPS NO<sub>2</sub>); Right: schematic of the signal generation in a CAPS instrument. | ||
The left panel of Figure 3 illustrates the key components of a CAPS instrument whereas the right panel sketches the signal generation. The signal background of the instruments is determined by the signal fluctuations when particle-free air (CAPS PMex) or air free of NO<sub>2</sub> (CAPS NO<sub>2</sub>) is sampled and originates from Rayleigh scattering of light by "air" molecules. The signal is determined by subtraction of the background signal (without particles/NO<sub>2</sub>) from the total signal (with particles/NO<sub>2</sub>). During operation, the instruments samples during pre-defined intervals particle-free or NO<sub>2</sub> – free air and determines the Rayleigh background of the instrument. Thus, the fluctuation of the background signal determines the limit of detection (LOD) of the instrument, i.e. the minimum detectable light extinction coefficient or NO<sub>2</sub> mixing ratio, respectively. | The left panel of Figure 3 illustrates the key components of a CAPS instrument whereas the right panel sketches the signal generation. The signal background of the instruments is determined by the signal fluctuations when particle-free air (CAPS PMex) or air free of NO<sub>2</sub> (CAPS NO<sub>2</sub>) is sampled and originates from Rayleigh scattering of light by "air" molecules. The signal is determined by subtraction of the background signal (without particles/NO<sub>2</sub>) from the total signal (with particles/NO<sub>2</sub>). During operation, the instruments samples during pre-defined intervals particle-free or NO<sub>2</sub> – free air and determines the Rayleigh background of the instrument. Thus, the fluctuation of the background signal determines the limit of detection (LOD) of the instrument, i.e. the minimum detectable light extinction coefficient or NO<sub>2</sub> mixing ratio, respectively. |