Laser Diode Array for Multiple Pollutant Monitoring

Infrared tunable diode laser spectrometers provide a highly effective means of measuring trace concentrations, with either remote sensing or with advective sampling. It is often desirable to measure more than one trace gas at a time. This is especially true when gas emissions are strongly correlated, such as in combustion emissions where measuring both the CO2 concentration and another minor constituent can immediately yield the emission rate of the minor constituent in terms of fuel use rate. Aerodyne Research, Inc., has shown recently that emission rates of several pollutant species by automobiles can be measured with high accuracy using a remote sensing system based on dual tunable diode lasers. This approach is the most accurate and sensitive technique available for on-road remote sensing of NO, CO, and other species. However, the present research instrument is optically complex, physically bulky, and expensive to deploy. In the innovation that Aerodyne proposes to develop, more laser diodes could be operated simultaneously, and the instrument size and complexity could be greatly reduced. These innovations could be applied to instruments that either measure remotely, by means of a long open atmospheric path, or that measure with advective sampling by means of a closed multi-pass optical cell.