Investigations of the Diurnal Variation of Vertical HCHO Profiles Based on MAX-DOAS Measurements in Beijing: Comparisons with OMI Vertical Column Data

Abstract

An investigation into the diurnal characteristics of vertical formaldehyde (HCHO) profiles was conducted based on multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Beijing during the CAREBEIJING campaign, covering a month-long period through August and September 2006. Vertical HCHO profiles were retrieved based on a combined differential optical absorption spectroscopy (DOAS) technique and an optimal estimation method (OEM). The HCHO volume-mixing ratio (VMR) was found to be highest in the layer from the surface up to an altitude of 1 km and to decrease with altitude above this layer. In all retrieved profiles, HCHO was not detected in the layer from 3-4 km. Over the diurnal cycle, the HCHO VMR values were generally highest at 15:00 local time (LT) and were lower in the morning and late afternoon. The mean HCHO VMRs were 6.17, 1.82, and 0.80 ppbv for the 0-1, 1-2, and 2-3-km layers, respectively, at 15:00 LT, whereas they were 3.54 (4.79), OPEN ACCESSAtmosphere 2015, 6 1817 1.06 (1.43), and 0.46 (0.63) ppbv for the 0-1, 1-2, and 2-3-km layers, respectively, at 09:00 (17:00) LT. The HCHO VMRs reached their highest values at 15:00 LT on August 19, which were 17.71, 5.20, and 2.31 ppbv for the 0-1, 1-2, and 2-3-km layers, respectively. This diurnal pattern implies that the photo-oxidation of volatile organic compounds (VOCs) was most active at 15:00 LT for several days during the campaign period. In a comparison of the derived HCHO VCDs with those obtained from the Ozone Monitoring Instrument (OMI) measurements, the HCHO vertical column density (VCD) values obtained from the OMI measurements tend to be smaller than those from the MAX-DOAS.

Ground-based MAX-DOAS observations of tropospheric formaldehyde VCDs and comparisons with the CAMS model at a rural site near Beijing during APEC 2014

“…Other smaller peaks appeared in the evening during other periods of busy traffic (16:00-18:00 LT), which might be caused by primary pollution sources, e.g., exhaust fumes from vehicles. Thus, the diurnal variations in HCHO during all three episodes were similar to the typical patterns of secondary sources as reported in Anderson et al (1996), Lee et al (2015), and Pinardi et al (2013). The absolute HCHO values during the APEC period were statistically lower than those in the pre-APEC and post-APEC periods.…”

“…The information obtained from MAX-DOAS measurements includes tropospheric column densities, surface volume mixing ratios (VMRs), and vertical profiles of aerosol extinction and trace gas mixing ratios. HCHO can be measured in the ultraviolet spectral range using the MAX-DOAS technique (Vigouroux et al, 2009;Wagner et al, 2011;Pinardi et al, 2013;Li et al, 2013;Borovski et al, 2014;Cheung et al, 2014;Franco et al, 2015;Lee et al, 2015;Schreier et al, 2016;Y. Wang et al, 2017a, b).…”

Retrieval Accuracy of HCHO Vertical Column Density from Ground-Based Direct-Sun Measurement and First HCHO Column Measurement Using Pandora

“…cm −2 . [17,50] with covariance between the HCHO SCD error and the AMF G error. No error is assumed for AMF G in the present study due to negligible scattering effects for the direct-sun measurement.…”

“…Therefore, we found, interestingly, that the maximum AOD effect on HCHO accuracy for the HCHO VCD value was 3.0 × 10 16 molecules cm −2 , for which both the noise effect at small HCHO VCD values and the high sensitivity effect at high HCHO VCD values are minimal. [17,50] with covariance between HCHO SCD error and AMF G error. No error is assumed for AMF G in the present study due to negligible scattering effects for the direct-sun measurement.…”

“…To determine the Pandora HCHO VCD retrieval errors, we calculated the error covariance of the spectral fitting errors, but with no errors associated with the direct-sun AMF G calculation (Figures 8 and 9). Then, the error covariance was used in the error propagation equation [17,50]. The error bars of the OMI HCHO VCD in Figure 9 were obtained from the OMI Level 2G product.…”