Optical remote sensing measurements using a UV DOAS system
- Unisearch Associates, Inc., Concord, Ontario (Canada)
An improved long-path differential optical absorption spectroscopy (DOAS) system in the ultraviolet-visible spectral region has been used to monitor a number of aromatic hydrocarbons as well as ozone and nitrogen dioxide. Measurements were performed in an industrial zone in suburban Toronto over an effective path length of 314 m. Benzene, toluene p-xylene, m-xylene, styrene and ozone were measured simultaneously in a 35 nm window centered at 260 nm. During another measurement period, data were collected for 5-minute intervals at two different wavelength regions. The aromatic hydrocarbons and ozone were monitored again around 260 nm and nitrogen dioxide was monitored around 355 nm. The sensitivity of the instrument for all species was found to be excellent. Measurements made with two co-located systems using the same retroreflector provided a measure of the instrumental detection limits. For all species the response of each instrument was linear with respect to the other and the linear regression plot of the two data sets provided standard errors of less than 0.5 ppbv for 5 minutes averaging periods and a 314 m path length. While the concentration of benzene typically measured was less than 10 ppbv throughout the measurement periods, toluene levels occasionally exceeded 300 ppbv. The measured concentrations of other species were less than 100 ppbv. These high levels of concentration were observed only during the first measurement period. Ozone levels exceeded 25 ppbv during the daytime except for the first measurement period when it was mostly cloudy and only reached a maximum of 8 ppbv. The simultaneous measurement of nitrogen dioxide and ozone showed anti-correlation in the variation of the concentration of these two species as expected from NO{sub x} and O{sub 3} chemistry.
- OSTI ID:
- 351229
- Report Number(s):
- CONF-970677--
- Country of Publication:
- United States
- Language:
- English
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