Application of the open path FTIR with COL1SB to measurements of ozone and VOCs in the urban area

The COnstrained L1-norm minimization with the Synthetic Background generation method (COL1SB) is newly developed open-path FTIR analysis software, designed to efficiently handle chemical interferences and to systematically generate background spectra. The performance of COL1SB was evaluated mainly against artificially generated field spectra. The present paper aims at application of COL1SB to ambient monitoring. In order to satisfy low detection limit requirements of ambient monitoring, COL1SB was further improved to accurately determine path averaged water vapor pressures, to dynamically select appropriate spectral bands, and to use site specific background spectra. The modified COL1SB was applied to measure ozone, ammonia, methane, carbon monoxide, and 26 VOC species in the park located at the urban area from 12:00 a.m., 25 May to 12:00 a.m., 26 May 2000. The open-path FTIR measurements for ozone, water vapor, alkane concentrations compared very well with those by sampling methods both in magnitudes and in diurnal variations. Furthermore, the detection rates of VOCs were considerably enhanced such that the detection rates based on the correlation coefficients appeared to be above 50% for 12 species out of 16 representative chemical species. Especially ethylene and isoprene, chemically reactive olefins, had high detection rates exceeding 80% despite of their low concentrations. These detection rates by COL1SB are 2–5 times higher than those derived by the conventional CLS method in the previous work (SPIE Conference on Environmental Monitoring and Remediation Technologies SPIE (1998) 3534, 140).