Characterization of urban CO column abundance with a portable low resolution spectrometer (PLRS): Comparisons with GOSAT and GEOS-Chem model data.

We presented the characterization of urban CO column abundance (XCO) in Hefei, China using a portable low resolution spectrometer (PLRS). An optimized correction spectrum was introduced in the spectral fitting to improve CO retrieval. A pronounced seasonal cycle and diurnal variation were observed with a precision of ~0.12%. The CO concentrations in winter are about 5-10ppm higher than those in summer. Most diurnal variations exhibited downward trends. The measurement in the early morning is about 2-5ppm higher than the late afternoon observation. The causes of the seasonal and diurnal trends were systematic analyzed. The coincident CO time series were compared with the Greenhouse Gases Observing SATellite (GOSAT) data and the GEOS-Chem global 3-D tropospheric chemistry model data. We found the ground based (g-b) PLRS data are systematically higher than the GOSAT and the GEOS-Chem data. Compared to the GOSAT data, the g-b PLRS data are 0.26ppm (0.07%) higher with a standard deviation of 1.70ppm (0.43%). Compared to the smoothed GEOS-Chem model data, the g-b PLRS data shows a 1.31ppm (0.33%) higher with a standard deviation of 5.30ppm (0.87%). The g-b PLRS generally reproduced the seasonal cycle observed by GOSAT and GEOS-Chem model with correlation coefficients (r) of 0.82 and 0.64, respectively.