Measurements of sulfur dioxide and formaldehyde in Taipei using a differential optical absorption spectrometer

Taipei, the capital city of Taiwan, lies in a basin, and its topography prevents the dispersion of pollutants in the city. As a continuation of our air quality study, from February 1999 through June 1999, we measured the concentrations of SO2 at six different locations and of formaldehyde at five locations using a differential optical absorption spectrometer (DOAS). The average concentration of SO2 varied from 3.5 to 6.6 ppb. The average concentration was highest at Toucheng because of its proximity to point sources. The level in Hsientien was close to that in Toucheng, with Hsinyu showing the lowest concentrations. The DOAS and the Taiwan Air Quality Monitoring Network (TAQMN) measurements for SO2 were highly correlated (r2 > 0.9) for Toucheng, Panchiao, and Hsientien. However, DOAS SO2 concentrations were 2 times higher for Hsientien and slightly lower for Panchiao than the TAQMN concentrations were. The average concentration of formaldehyde varied from 7 to 10 ppb. Diurnal variation of formaldehyde closely followed the variation of ozone, especially when the 1-hr peak ozone concentration was >60 ppb. Photochemical formation accounted for the ambient levels of formaldehyde in Taipei. Concentration of formaldehyde became significant on days when O3 concentration was high. Our results indicate that DOAS can replace conventional measurement techniques.