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OPTICAL REMOTE SENSING FOR AIR QUALITY MONITORING
Citation:
VARMA, R. M., R. A. HASHMONAY, R. H. KAGANN, M. T. MODRAK, M. BOLCH, B. D. HARRIS, AND B. J. KIM. OPTICAL REMOTE SENSING FOR AIR QUALITY MONITORING. Presented at Better Air Quality 2004, Agra, INDIA, December 06 - 08, 2004.
Impact/Purpose:
To inform the public.
Description:
The paper outlines recent developments in using optical remote sensing (ORS) instruments for air quality monitoring both for gaseous pollutants and airborne particulate matter (PM). The U.S. Environmental Protection Agency (EPA) has been using open-path Fourier transform infrared spectrometers (OP-FTIR), open-path tunable diode lasers (TDL) and ultra violet differential absorption spectroscopy (UV-DOAS) for monitoring pollutant gases from various sources. The use of a scanning ORS instrument and recently developed Radial Plume Mapping (RPM) configurations allows for near real-time flux estimation and source characterization for fugitive and area emissions. This method is expected to be published as an EPA Conditional Test Method (www.epa.gov/ttn/emc/tmethods.html) in the near future. Open path measurement projects performed by EPA and ARCADIS have characterized emissions from landfills, urban ambient air, vehicular exhausts, and industrial fence-line monitoring for various toxic pollutants. In addition to gaseous pollutants, airborne PM from various human and natural activities can also have a negative impact on ambient air quality, and this paper outlines recent developments in utilizing ORS instruments for PM monitoring. The extinction of light over a broad range of wavelengths from OP-FTIR and UV-DOAS spectrometers can be used to identify and characterize airborne PM. OP-FTIR absorbance spectra acquired during changing aerosol conditions reveal related changes in very broad baseline features specific to particular PM sources. Although undesirable for gas species quantification, these features can be used in conjunction with Mie theory of light scattering to retrieve PM size distribution. The success of recent ORS instrument applications indicates that the approaches discussed in this paper show significant promise for air quality monitoring and regulatory applications in India and other parts of Asia as well.