HCHO Vertical Column Densities Research Articles

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

Abstract. Formaldehyde (HCHO), a key aerosol precursor, plays a significant role in atmospheric photo-oxidation pathways. In this study, HCHO column densities were measured using a Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument at the University of Chinese Academy of Science (UCAS) in Huairou District, Beijing, which is about 50 km away from the city center. Measurements were taken during the period of 1 October 2014 to 31 December 2014, and the Asia-Pacific Economic Cooperation (APEC) summit was organized on 5–11 November. Peak values of HCHO vertical column densities (VCDs) around noon and a good correlation coefficient R2 of 0.73 between HCHO VCDs and surface O3 concentration during noontime indicated that the secondary sources of HCHO through photochemical reactions of volatile organic compounds (VOCs) dominated the HCHO values in the area around UCAS. Dependences of HCHO VCDs on wind fields and backward trajectories were identified and indicated that the HCHO values in the area around UCAS were considerably affected by the transport of pollutants (VOCs) from polluted areas in the south. The effects of control measures on HCHO VCDs during the APEC period were evaluated. During the period of the APEC conference, the average HCHO VCDs were ∼38%±20% and ∼30%±24% lower than that during the pre-APEC and post-APEC periods calculated at the 95 % confidence limit, respectively. This phenomenon could be attributed to both the effects of prevailing northwest wind fields during APEC and strict control measures. We also compared the MAX-DOAS results with the Copernicus Atmosphere Monitoring Service (CAMS) model. The HCHO VCDs of the CAMS model and MAX-DOAS were generally consistent with a correlation coefficient R2 greater than 0.68. The peak values were consistently captured by both data datasets, but the low values were systematically underestimated by the CAMS model. This finding may indicate that the CAMS model can adequately simulate the effects of the transport and the secondary sources of HCHO but underestimates the local primary sources.

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

In the present study, we investigate the effects of signal to noise (SNR), slit function (FWHM), and aerosol optical depth (AOD) on the accuracy of formaldehyde (HCHO) vertical column density (HCHOVCD) using the ground-based direct-sun synthetic radiance based on differential optical absorption spectroscopy (DOAS). We found that the effect of SNR on HCHO retrieval accuracy is larger than those of FWHM and AOD. When SNR = 650 (1300), FWHM = 0.6, and AOD = 0.2, the absolute percentage difference (APD) between the true HCHOVCD values and those retrieved ranges from 54 (30%) to 5% (1%) for the HCHOVCD of 5.0 × 1015 and 1.1 × 1017 molecules cm−2, respectively. Interestingly, the maximum AOD effect on the HCHO accuracy was found for the HCHOVCD of 3.0 × 1016 molecules cm−2. In addition, we carried out the first ground-based direct-sun measurements in the ultraviolet (UV) wavelength range to retrieve the HCHOVCD using Pandora in Seoul. The HCHOVCD was low at 12:00 p.m. local time (LT) in all seasons, whereas it was high in the morning (10:00 a.m. LT) and late afternoon (4:00 p.m. LT), except in winter. The maximum HCHOVCD values were 2.68 × 1016, 3.19 × 1016, 2.00 × 1016, and 1.63 × 1016 molecules cm−2 at 10:00 a.m. LT in spring, 10:00 a.m. LT in summer, 1:00 p.m. LT in autumn, and 9:00 a.m. LT in winter, respectively. The minimum values of Pandora HCHOVCD were 1.63 × 1016, 2.23 × 1016, 1.26 × 1016, and 0.82 × 1016 molecules cm−2 at around 1:45 p.m. LT in spring, summer, autumn, and winter, respectively. This seasonal pattern of high values in summer and low values in winter implies that photo-oxidation plays an important role in HCHO production. The correlation coefficient (R) between the monthly HCHOVCD values from Pandora and those from the Ozone Monitoring Instrument (OMI) is 0.61, and the slope is 1.25.

Spatiotemporal Variations in Satellite-Based Formaldehyde (HCHO) in the Beijing-Tianjin-Hebei Region in China from 2005 to 2015

The widespread distribution and strong seasonal pattern of highly concentrated summertime formaldehyde (HCHO) were observed using data from the Ozone Monitoring Instrument (OMI) onboard Aura satellite from 2005 to 2015 in Beijing-Tianjin-Hebei, China. The large-scale HCHO concentrations and its close connection with the surface O3 pollution made the study of summertime HCHO patterns and its major contributors necessary. Accordingly, time series decomposition, Moran’s I and Pearson correlation coefficient (PCC) were adopted to investigate the spatiotemporal variations of HCHO. We found that the HCHO columns regionally increased from 2005 to 2010 and decreased in the north (e.g., Chengde) from 2010 to 2015. Additionally, HCHO Vertical Column Densities (VCDs) exhibited higher values in urban areas. Despite the strong possibilities of major biogenic contributions, anthropogenic sources represented larger spatial PCCs and larger total emission rates. Industrial sources exhibited a large increasing emission amount, and the most similar distribution to HCHO was found in residential sources. By comparison, power-based emissions accounted for a relatively small fraction, and transportation emissions declined rapidly. In conclusion, anthropogenic VOCs might contribute to the summertime HCHO concentrations as well as isoprene, and controls on VOCs and HCHO would be greatly assisted by the satellite-based observations.

Sensitivity of formaldehyde (HCHO) column measurements from a geostationary satellite to temporal variation of the air mass factor in East Asia

Abstract. We examine upcoming geostationary satellite observations of formaldehyde (HCHO) vertical column densities (VCDs) in East Asia and the retrieval sensitivity to the temporal variation of air mass factors (AMFs) considering the presence of aerosols. Observation system simulation experiments (OSSE) were conducted using a combination of a global 3-D chemical transport model (GEOS-Chem), a radiative transfer model (VLIDORT), and a HCHO retrieval algorithm developed for the Geostationary Environment Monitoring Spectrometer (GEMS), which will be launched in 2019. Application of the retrieval algorithm to simulated hourly radiances yields the retrieved HCHO VCDs, which are then compared with the GEOS-Chem HCHO VCDs as true values for the evaluation of the retrieval algorithm. In order to examine the retrieval sensitivity to the temporal variation of AMF, we examine three AMF specifications, AMFm, AMFh, and AMFmh, using monthly, hourly, and monthly mean hourly input data for their calculation, respectively. We compare the retrieved HCHO VCDs using those three AMFs and find that the HCHO VCDs with AMFh are in better agreement with the true values than the results using AMFmh and AMFm. AMFmh reflects diurnal variation of planetary boundary layer and other meteorological parameters, so that the results with AMFmh show a better performance than those with AMFm. The differences between AMFh and AMFm range from −0.76 to 0.74 in absolute value and are mainly caused by temporal changes in aerosol chemical compositions and aerosol vertical distributions, which result in −27 to 58 and −34 to 43 % changes in HCHO VCDs over China, respectively, compared to HCHO VCDs using AMFm. We apply our calculated AMF table together with OMI aerosol optical properties to OMI HCHO products in March 2006, when Asian dust storms occurred, and find −32 to 47 % changes in the retrieved HCHO columns due to temporal changes in aerosol optical properties in East Asia. The impact of aerosol temporal variability cannot be neglected for future geostationary observations.

위성자료와 다중회귀분석법을 이용한 아시아 주요도시의 포름알데하이드 칼럼농도 추정연구

Abstract : A Multiple Regression Method (MRM) is used for the first time with Ozone MonitoringInstrument (OMI) and Moderate Resolution Imaging Spectroradiometer (MODIS) data to estimateformaldehyde (HCHO) Vertical Column Density (VCD). For a 3.5-year period from January 2005 throughJuly 2008, HCHO VCD estimation is investigated in cities over Asia in two categorized areas: (1) Majorcities in Northeast Asia (Beijing, Seoul, and Tokyo), (2) Major cities in Southeast Asia (New Delhi, Dhaka,and Bangkok). In the Major cities in Northeast Asia, there are good agreements between HCHO estimatedby the multiple linear regression method (HCHO MRM ) and HCHO measured by OMI (HCHO OMI ) (0.78 <R 2 < 0.82). However, in Major cities in Southeast Asia, there were poor agreements between HCHO OMI and HCHO MRM (0.24 < R 2 < 0.39). In addition, an unbiased assessment of the MRM performance usingmodeling and validation groups shows that the performance of the MRM based on separate modeling andvalidation groups is comparable to that using all the data for deriving Multiple Regression Equations(MREs). This study demonstrates that MRM can be an alternative tool for HCHO estimation in certainareas over Asia.Key Words : Multiple regression, OMI, MODIS, HCHO column, trace gas요약 :

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

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), 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.

Biogenic volatile compound emissions from a temperate forest, China: model simulation

Emissions of biogenic volatile organic compounds (BVOC) were measured using a relaxed eddy accumulation (REA) technique on an above-canopy tower in a temperate forest (Changbai Mountain, Jilin province, China) during the 2010 and 2011 summer seasons. Solar global radiation and photosynthetically active radiation (PAR) were also measured. Based on PAR energy dynamic balance, an empirical BVOC emission and PAR transfer model was developed that includes the processes of BVOC emissions and PAR transfer above the canopy level, including PAR absorption and consumption, and scattering by gases, liquids, and particles (GLPs). Simulated emissions of isoprene and monoterpenes were in agreement with observations. The averages of the relative estimator biases for the flux were 39.3 % for isoprene, and 27.1 % for monoterpenes in the 2010 and 2011 growing seasons, with NMSE (normalized mean square error) values of 0.133 and 0.101, respectively. The observed and simulated mean diurnal variations of isoprene and monoterpenes in the 2010 and 2011 growing seasons were evaluated for the validation of the empirical model. Under observed atmospheric conditions, the sensitivity analysis showed that emissions of isoprene and monoterpenes were more sensitive to changes in PAR than to water vapor content or to the magnitude of the scattering factor. The emissions of isoprene and monoterpenes in the 2010 and 2011 growing seasons (from June to September) were estimated using this empirical model along with hourly observational data, with mean hourly emissions of 1.71 and 1.55 mg m−2 h−1 for isoprene, and 0.48 and 0.47 mg m−2 h−1 for monoterpenes in 2010 and 2011, respectively. As formaldehyde (HCHO) is considered as the main oxidation product of isoprene and monoterpenes, it is necessary to investigate the link between HCHO and BVOC emissions. GOME-2 HCHO vertical column densities (VCDs) can be used to estimate BVOC emission fluxes in the Changbai Mountain temperate forest.

Inter-annual variations in satellite observations of nitrogen dioxide and formaldehyde over India

Nitrogen dioxide (NO2) and formaldehyde (HCHO) are important reactive trace gases due to their role regulating the oxidation capacity of the troposphere through ozone (O3) production and because they are pollutants causing health hazards. Over the last two decades, satellite and ground observations have reported a clear increase in the tropospheric HCHO and NO2 over India, with larger increases over the urban regions due to an increase in anthropogenic emissions. We compare observations from four different satellites for a period covering 1995–2013 over India. Some differences are observed in the calculated growth trends between the different satellites for both HCHO and NO2, although an increasing trend is seen by all the satellites. The mean growth rate calculated for the HCHO vertical column density (VCD) is 1.51 ± 0.44% yr−1, while tropospheric NO2 VCDs are calculated to calculated to grow faster at 2.20 ± 0.73% yr−1, indicating that NOx emissions are increasing faster than the emissions for volatile organic compounds (VOCs). The faster increase in NOx as compared to VOCs is however expected considering the large fraction of natural VOCs. The ratio of HCHO/NO2, which is an indicator of the relative sensitivity of surface ozone to emissions of nitrogen oxides (NOx = NO + NO2) and VOCs, is also studied. The satellite-derived ratios indicate that over most of India, O3 production is limited by NOx, although in urban regions and over the Indo-Gangetic Plain, the O3 production is VOC limited, especially during the winter season. We also compare the modeled HCHO and NO2 VCDs from the ECHAM5-HAMMOZ model using the RETRO emission inventory and the results indicate that the VOC emissions in the model are overestimated leading to larger modeled HCHO VCDs.

First measurements of formaldehyde integral content in the atmosphere using MAX-DOAS in the Moscow region

We present the first observations of formaldehyde (HCHO) atmospheric column performed for Zvenigorod, Moscow region, Russia. The data were retrieved from UV spectra of the scattered solar radiation measured by the multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument developed by the Japan Agency for Marine-Earth Science and Technology. We developed an algorithm for the HCHO retrieval from these spectra. For retrieval of the HCHO differential slant column densities, we used the DOAS settings used as baseline in the Cabauw Intercomparison Campaign of Nitrogen Dioxide Measuring Instruments (CINDI). The slant column densities of HCHO were converted to vertical column densities (VCDs) using the air mass factors calculated by a radiative transfer model. The determination of HCHO in the reference spectrum used multi-axis measurements.The variability of the HCHO vertical column in 2010 is analysed. The HCHO vertical column density is larger during east wind directions than during non-east wind directions. This can be associated with the Moscow Megacity influence on air quality at Zvenigorod. The estimation of the Moscow Megacity influence on HCHO abundance at Zvenigorod is around 2.5 × 1014 molec cm−2 per 1 km length of trajectory path inside the Moscow Ring Road.A temperature effect is noticeable in the HCHO VCD. Our data show a statistically significant positive temperature effect in HCHO for the background condition for temperatures from −5°C to +33°C. The temperature trend in HCHO data at Zvenigorod Scientific Station is about (8.9 ± 2.3) × 1014 molec cm−2 (°C)−1. The increase of the HCHO VCD during increase of the air temperature can be explained by the HCHO formation from non-methane biogenic volatile organic compounds (e.g. isoprene) for which more emission is expected at higher temperatures, and by growth of areas of forest and turf fires.

Assessing sources of uncertainty in formaldehyde air mass factors over tropical South America: Implications for top‐down isoprene emission estimates

We use a nested‐grid version of the GEOS‐Chem chemistry transport model, constrained by isoprene emissions from the Model of Emissions of Gases and Aerosols from Nature (MEGAN), and the Lund‐Potsdam‐Jena General Ecosystem Simulator (LPJ‐GUESS) bottom‐up inventories, to evaluate the impact that surface isoprene emissions have on formaldehyde (HCHO) air‐mass factors (AMFs) and vertical column densities (VCDs) over tropical South America during 2006, as observed by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and Ozone Monitoring Instrument (OMI). Although the large‐scale seasonal variability of monthly mean HCHO VCDs is typically unaffected by the choice of bottom‐up inventory, large relative differences of up to ±45% in the HCHO VCD can occur for individual regions and months, but typically most VCD differences are of order ±20%. These relative changes are comparable to those produced by other sources of uncertainty in the AMF including aerosols and surface albedo, but less than those from clouds. In a sensitivity test, we find that top‐down annual isoprene emissions inferred from SCIAMACHY and OMI HCHO vertical columns can vary by as much as ±30–50% for each instrument respectively, depending on the region studied and the a priori isoprene emissions used. Our analysis suggests that the influence of the a priori isoprene emissions on HCHO AMFs and VCDs is therefore non‐negligible and must be carefully considered when inferring top‐down isoprene emissions estimates over this, or potentially any other, region.

Interpreting elevated space-borne HCHO columns over the Mediterranean Sea using the OMI sensor

Abstract. Formaldehyde (HCHO) is an oxidation product of a wide range of volatile organic compounds (VOCs) and important atmospheric constituent found in both the polluted urban atmosphere and remote background sites. In this study, remotely sensed data of HCHO vertical column densities are analyzed over the Mediterranean Sea using the Ozone Monitoring Instrument (OMI). Data analysis indicates a marked seasonal cycle with a summer maximum and winter minimum confined to the marine environment during a three year period (2005–2007) examined. A possible retrieval artifact associated with Saharan dust transport over the region is explored by changing intensity of Saharan dust sources in GEOS-Chem following the recommendation of Generoso et al. (2008). Recalculated air mass factors (AMF), based on the new values of aerosol loadings, lead to a reduction of the summertime "hot spot" in OMI retrieval of HCHO vertical columns over the Mediterranean Sea; however, even after the correction, enhanced values are still present in this region. To explain these values, marine biogenic sources of VOCs are examined. Calculations indicate that emission of phytoplankton-produced isoprene is not likely to explain the enhanced HCHO vertical columns over the Mediterranean Sea. Model simulations in conjunction with measurements studies may be required to fully explore the complex mechanism of HCHO formation over the Mediterranean and its implications for the air quality in the region.