Infrared absorption measurement of carbon monoxide column abundance over Tokyo

We report column densities of carbon monoxide over Tokyo in November 1989–August 1991 derived from :infrared absorption measurement of the R(3) line of the 1-0 band at 2158 cm−1 by using the Sun as a light source. After removing the pollution component near the surface, we obtain CO column abundances ranging between 1.5 and 5 x 1018 molecules cm−2 which correspond to the burden of CO in the free troposphere. The lower envelope of the plot of the CO column density appears to indicate the background with a maximum of 2.5 x 1018 molecules cm−2 in spring and a minimum of 1.5 x 1018 molecules cm−2 in fall. The excess CO column above this level varies considerably and the variation exceeds the error due to uncertainty in the pollution layer thickness. The only likely explanation for the large day-to-day variability is anthropogenic emission; hence the free troposphere above Tokyo is also polluted by CO.