Process Analysis by AAVOS International

For the retrieval of trace gas amounts, the technique of Differential Optical Absorption Spectroscopy (DOAS) is a well established remote sensing method which has been developed and improved over the last decades. It was first used for measurements conducted with ground-based instruments, but can also be applied when observing the atmosphere from space. The DOAS method makes use of the individual absorption characteristics of molecules on the mathematical basis of Lambert-Beer’s absorption law. The technique enables to observe atmospheric trace gases such as ozone and NO2. For this the absorption in visible and near ultraviolet sunlight scattered in the zenith is measured. So called slant columns, that are the column densities along the light path can be derived. The fundamental difference between typical radiative transfer calculations and the point of view in the DOAS method is the way how the light is traced through the atmosphere. DOAS type measurements can be conducted either us...

Non-dispersive infrared sensors (NDIR) are simple spectroscopic devices often used as gas detectors for air pollution monitoring in the field. The non-dispersive instrument does not scan the spectrum, but instead is designed to look at that portion of the IR spectrum where the pollutant shows peak absorption. Gas concentration is measured electro-optically by its absorption of a specific wavelength in the infrared region. The NDIR detector has an optical filter in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb. A number of simple, rugged non-dispersive instruments have been designed for quantitative infrared analysis. They can be simple filter- or non-dispersive photometers, or instruments that employs filter wedges in lieu of a dispersing element. Some other instruments do not have wavelength selection device at all. Another type of IR analyser that is popular for analysing carbon monoxide in ambient air uses the gas-filter c...

Spectroscopy are optical methods for analysis of gaseous compounds. There are many techniques for gas analysis that involve observations of the electromagnetic radiation spectrum. The relevant part of the spectrum consists of: X-rays, ultraviolet, visible light and infrared. The ultraviolet, visible and IR regions are particularly relevant to gaseous air pollutant analysis, whereas X-ray methods are more relevant to particulate-phase pollutants and will not be discussed here.

Mass spectrometry (MS) is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio. These spectra are used to determine the elemental or isotopic signature of a sample, the masses of particles and of molecules, and to elucidate the chemical structures of molecules, such as peptides and other chemical compounds. In a typical MS procedure, a sample, which may be solid, liquid, or gas, is ionized, for example by bombarding it with electrons. This may cause some of the sample's molecules to break into charged fragments. These ions are then separated according to their mass-to-charge ratio, typically by accelerating them and subjecting them to an electric or magn...

Ultraviolet–visible spectroscopy or ultraviolet-visible spectrophotometry (UV-Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent ranges. The absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved. In this region of the electromagnetic spectrum, atoms and molecules undergo electronic transitions. Absorption spectroscopy is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state.

Raman spectroscopy (/ˈrɑːmən/; named after Indian physicist Sir C. V. Raman) is a spectroscopic technique used to observe vibrational, rotational, and other low-frequency modes in a system. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified. It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the vibrational modes in the system. Infrared spectroscopy yields similar, but complementary, information. Typically, a sample is illuminated with a laser beam. Electromagnetic radiation from the illuminated spot is collected with a lens and sent through a monochromator. Elastic scattered radiation at the wa...

Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) involves the interaction of infrared radiation with matter. It covers a range of techniques, mostly based on absorption spectroscopy. As with all spectroscopic techniques, it can be used to identify and study chemicals. Samples may be solid, liquid, or gas. The method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer (or spectrophotometer) to produce an infrared spectrum. An IR spectrum can be visualized in a graph of infrared light absorbance (or transmittance) on the vertical axis vs. frequency or wavelength on the horizontal axis. Typical units of frequency used in IR spectra are reciprocal centimeters (sometimes called wave numbers), with the symbol cm−1. Units of IR wavelength are commonly given in micrometers (formerly called "microns"), symbol μm, which are related to wave numbers in a reciprocal way. A common laboratory instrument that uses th...