Hazardous air pollutants monitor

An apparatus operable to detect the presence of selected gases in a sample, comprising:

• an infrared source operable to emit an infrared beam along a sight path intersecting the sample, and means for switching the infrared beam between an on-state and an off-state, the infrared beam exciting gases in the sample at particular excitation wavelengths when in the on-state, thereby causing the gases to emit light at certain emission wavelengths, and to absorb light at certain absorption wavelengths, the emission wavelengths and the absorption wavelengths being characteristic of particular component gases in the sample;
• viewing means directed along the sight path for collecting light from the gases in the sample responsive to the infrared beam;
• an acousto-optical tunable filter coupled to the viewing means, the tunable filter being operable controllably to diffract light collected by the viewing means for selecting particular optical wavelengths and to direct said particular optical wavelengths onto a detector;
• an analyzer coupled to the detector and to the tunable filter, the analyzer being operable to control the tunable filter for selecting a plurality of said particular optical wavelengths and to discriminate for presence of said particular component gases by determining a characteristic pattern of the emission and absorption wavelengths detected;
• and,
• wherein the analyzer is operable to collect emission wavelengths during the off-state of the infrared source.

A method for measuring atmospheric gases in a sample, comprising the steps of:

• directing an infrared beam through the sample, so as to excite the sample and cause the sample to emit and to absorb light at particular wavelengths that are characteristic of component molecules in the sample;
• receiving light from the sample and applying the light to an acousto-optical tunable filter having means for applying an acoustic wave at a predetermined frequency for diffracting the light into a spectrum, and applying the light to a detector means;
• varying the predetermined frequency to select among a plurality of wavelengths of absorption and emission at the particular wavelengths that are characteristic of the component molecules;
• measuring a level of the light at said particular wavelengths;
• analyzing a pattern of the light received from the sample, at the particular wavelengths, for detecting the component molecules in the sample.

A method for measuring atmospheric gases in a sample, comprising the steps of:

• providing an exciting infrared light beam and means to emit the light beam at selected wavelengths along a beam path intersecting the sample such that the selected wavelengths of the infrared light beam excite component molecules in the sample;
• receiving infrared radiation from the sample, the infrared radiation having absorption and emission spectra characteristic of the component molecules;
• applying the infrared radiation to an acousto-optical tunable filter and an associated detector means, and tuning the filter by applying to the filter an acoustic wave at an predetermined frequency to diffract the infrared radiation such that a selected wavelength is applied to the detector;
• measuring a level of said infrared radiation at the selected wavelength;
• tuning the filter by successively applying additional frequencies, measuring the level at the additional selected wavelengths, and proceeding through a set of frequencies sufficient to define the absorption and emission spectra of the sample;
• and,
• determining the component molecules of the sample from the absorption and emission spectra.