The influence of instrumental line shape degradation on NDACC gas retrievals: Total column and profile

We simulated instrumental line shape (ILS) degradations with respect to typical types of misalignment, and compared their influence on each NDACC (Network for Detection of Atmospheric Composition Change) gas. The sensitivities of the total column, the root mean square (rms) of the fitting residual, the total random uncertainty, the total systematic uncertainty, the total uncertainty, degrees of freedom for signal (DOFs), and the profile with respect to different levels of ILS degradation for all current standard NDACC gases, i.e. O3, HNO3, HCl, HF, ClONO2, CH4, CO, N2O, C2H6, and HCN, were investigated. The influence of an imperfect ILS on NDACC gases’ retrieval was assessed, and the consistency under different meteorological conditions and solar zenith angles (SZAs) were examined. The study concluded that the influence of ILS degradation can be approximated by the linear sum of individual modulation efficiency (ME) amplitude influence and phase error (PE) influence. The PE influence is of secondary importance compared with the ME amplitude. Generally, the stratospheric gases are more sensitive to ILS degradation than the tropospheric gases, and the positive ME influence is larger than the negative ME. For a typical ILS degradation (10 %), the total columns of stratospheric gases O3, HNO3, HCl, HF, and ClONO2 changed by 1.9, 0.7, 4, 3, and 23 %, respectively, while the columns of tropospheric gases CH4, CO, N2O, C2H6, and HCN changed by 0.04, 2.1, 0.2, 1.1, and 0.75 %, respectively. In order to suppress the fractional difference in the total column for ClONO2 and other NDACC gases within 10 and 1 %, respectively, the maximum positive ME degradations for O3, HNO3, HCl, HF, ClONO2, CO, C2H6, and HCN should be less than 6, 15, 5, 5, 5, 5, 9, and 13 %, respectively; the maximum negative ME degradations for O3, HCl, and HF should be less than 6, 12, and 12 %, respectively; the influence of ILS degradation on CH4 and N2O can be regarded as being negligible

Long-term tropospheric formaldehyde concentrations deduced from ground-based fourier transform solar infrared measurements

International audienceLong-term total column measurements of formaldehyde (HCHO) covering a 12 year period from 1992 to 2004 are reported from spectra recorded with a high-resolution Fourier Transform Spectrometer (FTS) using the sun as a light source at a Southern Hemisphere site (Lauder, New Zealand). The ambient HCHO concentrations at this rural location are often at background levels (15 molecules cm?2, the maximum occurring in the summer. A simple box model of CH4 oxidation reproduces the seasonal cycle, but significantly underestimates the maximum HCHO ground concentrations deduced from the column observations, particularly in summer. This implies the existence of a significant source of HCHO that cannot be explained by oxidation of CH4 alone. The ground-based FTS column data compares well with collocated HCHO column measurements from the Global Ozone Monitoring Experiment (GOME) satellite instrument (r2=0.65, mean bias=10%, n=48)

Ozone seasonal evolution and photochemical production regime in the polluted troposphere in eastern China derived from high-resolution Fourier transform spectrometry (FTS) observations

The seasonal evolution of O3 and its photochemical production regime in a polluted region of eastern China between 2014 and 2017 has been investigated using observations. We used tropospheric ozone (O3), carbon monoxide (CO), and formaldehyde (HCHO, a marker of VOCs (volatile organic compounds)) partial columns derived from high-resolution Fourier transform spectrometry (FTS); tropospheric nitrogen dioxide (NO2, a marker of NOx (nitrogen oxides)) partial column deduced from the Ozone Monitoring Instrument (OMI); surface meteorological data; and a back trajectory cluster analysis technique. A broad O3 maximum during both spring and summer (MAM/JJA) is observed; the day-to-day variations in MAM/JJA are generally larger than those in autumn and winter (SON/DJF). Tropospheric O3 columns in June are 1.55x1018moleculescm-2 (56DU (Dobson units)), and in December they are 1.05x1018moleculescm-2 (39 DU). Tropospheric O3 columns in June were ∼ 50% higher than those in December. Compared with the SON/DJF season, the observed tropospheric O3 levels in MAM/JJA are more influenced by the transport of air masses from densely populated and industrialized areas, and the high O3 level and variability in MAM/JJA is determined by the photochemical O3 production. The tropospheric-column HCHO/NO2 ratio is used as a proxy to investigate the photochemical O3 production rate (PO3). The results show that the PO3 is mainly nitrogen oxide (NOx) limited in MAM/JJA, while it is mainly VOC or mixed VOC-NOx limited in SON/DJF. Statistics show that NOx-limited, mixed VOC-NOx-limited, and VOC-limited PO3 accounts for 60.1%, 28.7%, and 11% of days, respectively. Considering most of PO3 is NOx limited or mixed VOC-NOx limited, reductions in NOx would reduce O3 pollution in eastern China

Improved ozone monitoring by ground-based FTIR spectrometry

Accurate observations of atmospheric ozone (O3) are essential to monitor in detail its key role in atmospheric chemistry. The present paper examines the performance of different O3 retrieval strategies from FTIR (Fourier transform infrared) spectrometry by using the 20-year time series of the high-resolution solar spectra acquired from 1999 to 2018 at the subtropical Izaña Observatory (IZO, Spain) within NDACC (Network for the Detection of Atmospheric Composition Change). In particular, the effects of two of the most influential factors have been investigated: the inclusion of a simultaneous atmospheric temperature profile fit and the spectral O3 absorption lines used for the retrievals (the broad spectral region of 1000–1005 cm−1 and single microwindows between 991 and 1014 cm−1 ). Additionally, the water vapour (H2O) interference in O3 retrievals has been evaluated, with the aim of providing an improved O3 strategy that minimises its impact and, therefore, could be applied at any NDACC FTIR station under different humidity conditions. The theoretical and experimental quality assessments of the different FTIR O3 products (total column (TC) amounts and volume mixing ratio (VMR) profiles) provide consistent results.This research research has been supported by the European Research Council under FP7/(2007–2013)/ERC grant agreement no. 256961 (project MUSICA), by the Deutsche Forschungsgemeinschaft for the project MOTIV (Geschäftszeichen SCHN 1126/2-1), by the Ministerio de Economía y Competitividad of Spain through the projects CGL2012-37505 (project NOVIA) and CGL2016-80688- P (project INMENSE), and by EUMETSAT under its fellowship programme (project VALIASI)

Long-term tropospheric formaldehyde concentrations deduced from ground-based fourier transform solar infrared measurements

We report a 13-year (1992–2005) dataset of total column measurements of formaldehyde (HCHO) over Lauder, New Zealand, inferred from solar infrared spectra measured using a high-resolution Fourier Transform Spectrometer (FTS). Ambient HCHO concentrations at this rural location are often close to levels typical of remote marine environments (\u3c250 ppt), which are close to the detection limit using standard techniques. Consequently we develop a new method that successfully produces HCHO columns with sufficient sensitivity throughout the whole season. HCHO columns over Lauder have a strong seasonal cycle (±50%), with a mean column of 4.9×1015 molecules cm−2, peaking during summer months. A simple box model of CH4 oxidation reproduces the observed broad-scale seasonal cycle, but significantly underestimates the seasonal peak HCHO ground concentrations during summer. This suggests the existence of an additional significant source of HCHO, possibly isoprene that cannot be explained by oxidation of CH4 alone. The ground-based FTS column data compare well with collocated HCHO column measurements from the Global Ozone Monitoring Experiment (GOME) satellite instrument during the operational period of GOME (1996–2001, r2=0.65, mean bias=10%, n=48)

Long-term tropospheric formaldehyde concentrations deduced from ground-based fourier transform solar infrared measurements

We report a 13-year (1992–2005) dataset of total column measurements of formaldehyde (HCHO) over Lauder, New Zealand, inferred from solar infrared spectra measured using a high-resolution Fourier Transform Spectrometer (FTS). Ambient HCHO concentrations at this rural location are often close to levels typical of remote marine environments (\u3c250 ppt), which are close to the detection limit using standard techniques. Consequently we develop a new method that successfully produces HCHO columns with sufficient sensitivity throughout the whole season. HCHO columns over Lauder have a strong seasonal cycle (±50%), with a mean column of 4.9×1015 molecules cm−2, peaking during summer months. A simple box model of CH4 oxidation reproduces the observed broad-scale seasonal cycle, but significantly underestimates the seasonal peak HCHO ground concentrations during summer. This suggests the existence of an additional significant source of HCHO, possibly isoprene that cannot be explained by oxidation of CH4 alone. The ground-based FTS column data compare well with collocated HCHO column measurements from the Global Ozone Monitoring Experiment (GOME) satellite instrument during the operational period of GOME (1996–2001, r2=0.65, mean bias=10%, n=48)

Improved ozone monitoring by ground-based FTIR spectrometry

Accurate observations of atmospheric ozone (O$_3$) are essential to monitor in detail its key role in atmospheric chemistry. The present paper examines the performance of different O$_3$ retrieval strategies from FTIR (Fourier transform infrared) spectrometry by using the 20-year time series of the high-resolution solar spectra acquired from 1999 to 2018 at the subtropical Izaña Observatory (IZO, Spain) within NDACC (Network for the Detection of Atmospheric Composition Change). In particular, the effects of two of the most influential factors have been investigated: the inclusion of a simultaneous atmospheric temperature profile fit and the spectral O$_3$ absorption lines used for the retrievals (the broad spectral region of 1000–1005 cm$_{−1}$ and single micro-windows between 991 and 1014 cm$_{−1}$). Additionally, the water vapour (H$_{2}$O) interference in O$_3$ retrievals has been evaluated, with the aim of providing an improved O$_3$ strategy that minimises its impact and, therefore, could be applied at any NDACC FTIR station under different humidity conditions. The theoretical and experimental quality assessments of the different FTIR O$_3$ products (total column (TC) amounts and volume mixing ratio (VMR) profiles) provide consistent results. Combining a simultaneous temperature retrieval with the optimal selection of single O$_3$ micro-windows results in superior FTIR O$_3$ products, with a precision of better than 0.6%–0.7% for O$_3$ TCs as compared to coincident NDACC Brewer observations taken as a reference. However, this improvement can only be achieved provided the FTIR spectrometer is properly characterised and stable over time. For unstable instruments, the temperature fit is found to exhibit a strong negative influence on O$_3$ retrievals due to the increase in the cross-interference between the temperature retrieval and instrumental performance (given by the instrumental line shape function and measurement noise), which leads to a worsening of the precision of FTIR O$_3$ TCs of up to 2 %. This cross-interference becomes especially noticeable beyond the upper troposphere/lower stratosphere, as documented theoretically as well as experimentally by comparing FTIR O$_3$ profiles to those measured using electrochemical concentration cell (ECC) sondes within NDACC. Consequently, it should be taken into account for the reliable monitoring of the O$_3$ vertical distribution, especially over long-term timescales

Observations of Atmospheric Gases Using Fourier Transform Spectrometers

Remote sensing of atmospheric gases improves our understanding of the state and evolution of the Earth’s environment. At the beginning of the thesis, the basic principles for the retrieval of concentrations of atmospheric gases from spectra are presented with a focus on ground-based observations. An overview of the characteristic features of different platforms, viewing geometries, measurement sites, and Fourier Transform Spectrometers (FTSs) used in the measurements are provided. The thesis covers four main projects. The first study of the global distribution of atmospheric phosgene was carried out using a total of 5614 measured profiles from the satellite-borne Atmospheric Chemistry Experiment FTS (ACE-FTS) spanning the period February 2004 through May 2006. The phosgene concentrations display a zonally symmetric pattern with the maximum concentration located approximately over the equator, at about 25 km in altitude, and the concentrations decrease towards the poles. A layer of enhanced concentration of phosgene spans the lower stratosphere at all latitudes, with volume mixing ratios of 20-60 pptv. The reasons for the formation of the phosgene distribution pattern are explained by the insolation, lifetime of phosgene and the Brewer-Dobson circulation. The ACE observations show lower phosgene concentrations in the stratosphere than were obtained from previous observations in the 1980s and 1990s due to a significant decrease in source species. The Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR) is a copy of the ACE-FTS that was designed for ground-based and balloon-borne measurements. The first balloon flight was part of the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) 2004 balloon payload. Some useful engineering information was obtained on the thermal performance of the instrument during the flight. As part of the MANTRA program, a ground-based inter-instrument comparison campaign was conducted with the objective of assessing instrument performance, and evaluating data processing routines and retrieval codes. PARIS-IR provides similar quality results for stratospheric species as does the University of Toronto FTS. An advanced study was carried out for the Carbon Cycle science by Fourier Transform Spectroscopy (CC-FTS) mission, which is a proposed future satellite mission to obtain a better understanding of the sources and sinks of greenhouse gases in the Earth’s atmosphere by monitoring total and partial columns of CO2, CH4, N2O, and CO in the near infrared together with the molecular O2 column. To evaluate the spectral regions, resolution, optical components, and spectroscopic parameters required for the mission, ground-based Fourier transform spectra, recorded at Kiruna, Kitt Peak, and Waterloo, were used. Dry air volume mixing ratios of CO2 and CH4 were retrieved from the ground-based observations. A FTS with a spectral resolution of 0.1 cm-1, operating between 2000 and 15000 cm-1, is suggested as the primary instrument for the mission. Further progress in improving the atmospheric retrievals for CO2, CH4 and O2 requires new laboratory measurements to improve the spectroscopic line parameters. Atmospheric observations were made with three FTSs at the Polar Environment Atmospheric Research Laboratory (PEARL) during spring 2006. The vertical column densities of O3, HCl, HNO3, HF, NO2, ClONO2 and NO from PARIS-IR, the Eureka DA8 FTS, and the ACE-FTS show good agreement. Chorine activation and denitrification in the Arctic atmosphere were observed in the extremely cold stratosphere near Eureka, Nunavut, Canada. The observed ozone depletion during the 2006 campaign was attributed to chemical removal