The Network for the Detection of Atmospheric Composition Change (NDACC) is an international global network of more than 90 stations making high-quality measurements of atmospheric composition that ...began official operations in 1991 after 5 years of planning. Apart from sonde measurements, all measurements in the network are performed by ground-based remote-sensing techniques. Originally named the Network for the Detection of Stratospheric Change (NDSC), the name of the network was changed to NDACC in 2005 to better reflect the expanded scope of its measurements. The primary goal of NDACC is to establish long-term databases for detecting changes and trends in the chemical and physical state of the atmosphere (mesosphere, stratosphere, and troposphere) and to assess the coupling of such changes with climate and air quality. NDACC's origins, station locations, organizational structure, and data archiving are described. NDACC is structured around categories of ground-based observational techniques (sonde, lidar, microwave radiometers, Fourier-transform infrared, UV-visible DOAS (differential optical absorption spectroscopy)-type, and Dobson-Brewer spectrometers, as well as spectral UV radiometers), timely cross-cutting themes (ozone, water vapour, measurement strategies, cross-network data integration), satellite measurement systems, and theory and analyses. Participation in NDACC requires compliance with strict measurement and data protocols to ensure that the network data are of high and consistent quality. To widen its scope, NDACC has established formal collaborative agreements with eight other cooperating networks and Global Atmosphere Watch (GAW). A brief history is provided, major accomplishments of NDACC during its first 25 years of operation are reviewed, and a forward-looking perspective is presented.
TROPOMI (the TROPOspheric Monitoring Instrument), on board the Sentinel-5 Precursor (S5P) satellite, has been monitoring the Earth's atmosphere since October 2017 with an unprecedented horizontal ...resolution (initially 7 km2×3.5 km2, upgraded to 5.5 km2×3.5 km2 in August 2019). Monitoring air quality is one of the main objectives of TROPOMI; it obtains measurements of important pollutants such as nitrogen dioxide, carbon monoxide, and formaldehyde (HCHO). In this paper we assess the quality of the latest HCHO TROPOMI products versions 1.1.(5-7), using ground-based solar-absorption FTIR (Fourier-transform infrared) measurements of HCHO from 25 stations around the world, including high-, mid-, and low-latitude sites.
Most of these stations are part of the Network for the Detection of Atmospheric Composition Change (NDACC), and they provide a wide range of observation conditions, from very clean remote sites to those with high HCHO levels from anthropogenic or biogenic emissions. The ground-based HCHO retrieval settings have been optimized and harmonized at all the stations, ensuring a consistent validation among the sites. In this validation work, we first assess the accuracy of TROPOMI HCHO tropospheric columns using the median of the relative differences between TROPOMI and FTIR ground-based data (BIAS). The pre-launch accuracy requirements of TROPOMI HCHO are 40 %–80 %. We observe that these requirements are well reached, with the BIAS found below 80 % at all the sites and below 40 % at 20 of the 25 sites. The provided TROPOMI systematic uncertainties are well in agreement with the observed biases at most of the stations except for the highest-HCHO-level site, where it is found to be underestimated. We find that while the BIAS has no latitudinal dependence, it is dependent on the HCHO concentration levels: an overestimation (+26±5 %) of TROPOMI is observed for very low HCHO levels (<2.5×1015 molec. cm−2), while an underestimation (-30.8%±1.4 %) is found for high HCHO levels (>8.0×1015 molec. cm−2). This demonstrates the great value of such a harmonized network covering a wide range of concentration levels, the sites with high HCHO concentrations being crucial for the determination of the satellite bias in the regions of emissions and the clean sites allowing a small TROPOMI offset to be determined. The wide range of sampled HCHO levels within the network allows the robust determination of the significant constant and proportional TROPOMI HCHO biases (TROPOMI =+1.10±0.05 ×1015+0.64±0.03 × FTIR; in molecules per square centimetre). Second, the precision of TROPOMI HCHO data is estimated by the median absolute deviation (MAD) of the relative differences between TROPOMI and FTIR ground-based data. The clean sites are especially useful for minimizing a possible additional collocation error. The precision requirement of 1.2×1016 molec. cm−2 for a single pixel is reached at most of the clean sites, where it is found that the TROPOMI precision can even be 2 times better (0.5–0.8×1015 molec. cm−2 for a single pixel). However, we find that the provided TROPOMI random uncertainties may be underestimated by a factor of 1.6 (for clean sites) to 2.3 (for high HCHO levels). The correlation is very good between TROPOMI and FTIR data (R=0.88 for 3 h mean coincidences; R=0.91 for monthly means coincidences). Using about 17 months of data (from May 2018 to September 2019), we show that the TROPOMI seasonal variability is in very good agreement at all of the FTIR sites. The FTIR network demonstrates the very good quality of the TROPOMI HCHO products, which is well within the pre-launch requirements for both accuracy and precision. This paper makes suggestions for the refinement of the TROPOMI random uncertainty budget and TROPOMI quality assurance values for a better filtering of the remaining outliers.
Throughout spring and summer 2020, ozone stations in the northern extratropics recorded unusually low ozone in the free troposphere. From April to August, and from 1 to 8 kilometers altitude, ozone ...was on average 7% (≈4 nmol/mol) below the 2000–2020 climatological mean. Such low ozone, over several months, and at so many stations, has not been observed in any previous year since at least 2000. Atmospheric composition analyses from the Copernicus Atmosphere Monitoring Service and simulations from the NASA GMI model indicate that the large 2020 springtime ozone depletion in the Arctic stratosphere contributed less than one-quarter of the observed tropospheric anomaly. The observed anomaly is consistent with recent chemistry-climate model simulations, which assume emissions reductions similar to those caused by the COVID-19 crisis. COVID-19 related emissions reductions appear to be the major cause for the observed reduced free tropospheric ozone in 2020.
We present a multiyear time series of column abundances of carbon monoxide (CO), hydrogen cyanide (HCN), and ethane (C2H6) measured using Fourier-transform infrared (FTIR) spectrometers at 10 sites ...affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC). Six are high-latitude sites: Eureka, Ny-Ålesund, Thule, Kiruna, Poker Flat, and St. Petersburg, and four are midlatitude sites: Zugspitze, Jungfraujoch, Toronto, and Rikubetsu. For each site, the interannual trends and seasonal variabilities of the CO time series are accounted for, allowing background column amounts to be determined. Enhancements above the seasonal background were used to identify possible wildfire pollution events. Since the abundance of each trace gas emitted in a wildfire event is specific to the type of vegetation burned and the burning phase, correlations of CO to the long-lived wildfire tracers HCN and C2H6 allow for further confirmation of the detection of wildfire pollution. A GEOS-Chem tagged CO simulation with Global Fire Assimilation System (GFASv1.2) biomass burning emissions was used to determine the source attribution of CO concentrations at each site from 2003 to 2018. For each detected wildfire pollution event, FLEXPART back-trajectory simulations were performed to determine the transport times of the smoke plume. Accounting for the loss of each species during transport, the enhancement ratios of HCN and C2H6 with respect to CO were converted to emission ratios. We report mean emission ratios with respect to CO for HCN and C2H6 of 0.0047 and 0.0092, respectively, with a standard deviation of 0.0014 and 0.0046, respectively, determined from 23 boreal North American wildfire events. Similarly, we report mean emission ratios for HCN and C2H6 of 0.0049 and 0.0100, respectively, with a standard deviation of 0.0025 and 0.0042, respectively, determined from 39 boreal Asian wildfire events. The agreement of our emission ratios with literature values illustrates the capability of ground-based FTIR measurements to quantify biomass burning emissions. We provide a comprehensive dataset that quantifies HCN and C2H6 emission ratios from 62 wildfire pollution events. Our dataset provides novel emission ratio estimates, which are sparsely available in the published literature, particularly for boreal Asian sources.
Abstract
On 2017 August 21, the Airborne Infrared Spectrometer (AIR-Spec) observed the total solar eclipse at an altitude of 14 km from aboard the NSF/NCAR Gulfstream V research aircraft. The ...instrument successfully observed the five coronal emission lines that it was designed to measure: Si
x
1.431
μ
m, S
xi
1.921
μ
m, Fe
ix
2.853
μ
m, Mg
viii
3.028
μ
m, and Si
ix
3.935
μ
m. Characterizing these magnetically sensitive emission lines is an important first step in designing future instruments to monitor the coronal magnetic field, which drives space weather events, as well as coronal heating, structure, and dynamics. The AIR-Spec instrument includes an image stabilization system, feed telescope, grating spectrometer, and slit-jaw imager. This paper details the instrument design, optical alignment method, image processing, and data calibration approach. The eclipse observations are described and the available data are summarized.
Stratospheric circulation is a critical part of the Arctic ozone cycle.
Sudden stratospheric warming events (SSWs) manifest the strongest alteration
of stratospheric dynamics. During SSWs, changes in ...planetary wave
propagation vigorously influence zonal mean zonal wind, temperature, and
tracer concentrations in the stratosphere over the high latitudes. In this
study, we examine six persistent major SSWs from 2004 to 2020 using the
Modern-Era Retrospective analysis for Research and Applications, Version 2
(MERRA-2). Using the unique density of observations around the Greenland
sector at high latitudes, we perform comprehensive comparisons of high-latitude observations with the MERRA-2 ozone dataset during the six major
SSWs. Our results show that MERRA-2 captures the high variability of mid-stratospheric ozone fluctuations during SSWs over high latitudes. However,
larger uncertainties are observed in the lower stratosphere and troposphere.
The zonally averaged stratospheric ozone shows a dramatic increase of
9 %–29 % in total column ozone (TCO) near the time of each SSW, which lasts
up to 2 months. This study shows that the average shape of the Arctic
polar vortex before SSWs influences the geographical extent, timing, and
magnitude of ozone changes. The SSWs exhibit a more significant impact on
ozone over high northern latitudes when the average polar vortex is mostly
elongated as seen in 2009 and 2018 compared to the events in which the polar
vortex is displaced towards Europe. Strong correlation (R2=90 %) is
observed between the magnitude of change in average equivalent potential
vorticity before and after SSWs and the associated averaged total column
ozone changes over high latitudes. This paper investigates the different
terms of the ozone continuity equation using MERRA-2 circulation, which
emphasizes the key role of vertical advection in mid-stratospheric ozone
during the SSWs and the magnified vertical advection in elongated vortex
shape as seen in 2009 and 2018.
This proof‐of‐concept study demonstrates that methane (CH4) emissions from natural gas (NG) and agriculture can be disentangled using the concept of excess column observations. A network of ...cost‐effective sensors measured excess column‐averaged dry‐air mole fractions for CH4 (ΔXCH4), ethane (ΔXC2H6 as NG tracer), and ammonia (ΔXNH3 from agriculture) in the Denver‐Julesburg Basin during March 2015. ΔXCH4 varied up to 17 ppb and was >3 times higher with winds from directions where NG is produced. The ΔXCH4 variance is explained by variations in the C2H6‐NH3 tracer pair, attributing 63 ± 17% to NG, 25 ± 10% to agriculture, and 12 ± 12% to other sources. The ratios ΔXC2H6/ΔXCH4 (16 ± 2%; indicates wet NG) and ΔXNH3/ΔXCH4 (43 ± 12%) were compatible with in situ measured ratios. Excess columns are independent of boundary layer height, characterize gases in the open atmosphere, are inherently calibrated, average over extended spatial scales, and provide a complementary perspective to quantify and attribute CH4 emissions on regional scales.
Plain Language Summary
Methane is the second most important anthropogenic greenhouse gas. Knowledge about methane sources is increasingly relevant as energy production continues to shift toward natural gas and becomes complicated by collocated emissions from natural gas production and agriculture due to shared land use. There is a need for methods to better decouple emissions from multiple sources that contribute to local enhancements in methane, which are small compared to the regional methane background concentrations, and depend on atmospheric transport and planetary boundary layer height. In this study, we show that the concept of collocated excess column measurements of methane and chemical tracers shows great promise as a viable approach to disentangle methane emissions from multiple sources by means of cost‐effective networks of ground‐based sensors. Excess columns are independent of boundary layer height, which makes quantification and source attribution of methane more straightforward.
Key Points
Methane emissions from natural gas and agriculture can be separated using the concept of excess column measurements of source tracers
Column integrals over boundary layer height are complementary to in situ methods and useful to quantify and source apportion methane on regional scales
Natural gas sources dominate over agricultural and other sources, but the latter are relatively more important when excess CH4 is smaller than 5 ppb
Boreal fires have increased during the last years and are projected to become more intense and frequent as a consequence of climate change. Wildfires produce a wide range of effects on the Arctic ...climate and ecosystem, and understanding these effects is crucial for predicting the future evolution of the Arctic region. This study focuses on the impact of the long-range transport of biomass-burning aerosol into the atmosphere and the corresponding radiative perturbation in the shortwave frequency range. As a case study, we investigate an intense biomass-burning (BB) event which took place in summer 2017 in Canada and subsequent northeastward transport of gases and particles in the plume leading to exceptionally high values (0.86) of Aerosol Optical Depth (AOD) at 500 nm measured in northwestern Greenland on 21 August 2017. This work characterizes the BB plume measured at the Thule High Arctic Atmospheric Observatory (THAAO; 76.53∘N, 68.74∘W) in August 2017 by assessing the associated shortwave aerosol direct radiative impact over the THAAO and extending this evaluation over the broader region (60∘N–80∘N, 110∘W–0∘E). The radiative transfer simulations with MODTRAN6.0 estimated an aerosol heating rate of up to 0.5 K/day in the upper aerosol layer (8–12 km). The direct aerosol radiative effect (ARE) vertical profile shows a maximum negative value of −45.4 Wm−2 for a 78∘ solar zenith angle above THAAO at 3 km altitude. A cumulative surface ARE of −127.5 TW is estimated to have occurred on 21 August 2017 over a portion (∼3.1×106 km2) of the considered domain (60∘N–80∘N, 110∘W–0∘E). ARE regional mean daily values over the same portion of the domain vary between −65 and −25 Wm−2. Although this is a limited temporal event, this effect can have significant influence on the Arctic radiative budget, especially in the anticipated scenario of increasing wildfires.
When retrieving geophysical parameters, it is advantageous to have an estimate of prior information that is based on observations with associated uncertainties, but this is often not possible. ...Long-term ground-based remote sensing measurements and the ozonesonde program at Summit Station, Greenland, provide an opportunity to create a unique framework to retrieve atmospheric ozone using observationally based prior information in the Arctic. This study investigates the potential of using the ground-based polar atmospheric emitted radiance interferometer (P-AERI) to estimate ozone below 10 km. Downlooking or limb-viewing sensors, such as those from satellites, have limited sensitivity to the lower atmosphere; however, uplooking, ground-based instruments provide complementary information to satellite observations to improve trace gas estimates at lower atmospheric levels. Modern-Era Retrospective Analysis for Research and Application, version 2 (MERRA-2) is a reanalysis product that integrates satellite information but also inherits their higher uncertainties at lower atmospheric levels. An observation-based climatology of the uncertainty in the MERRA-2 ozone dataset is estimated using ozonesondes launched at Summit Station. MERRA-2 shows high accuracy in the middle stratosphere but larger uncertainties below 10 km. Retrievals that use spectral radiance measurements from the P-AERI improve the estimates of ozone concentrations in the troposphere and lower stratosphere by using prior information from MERRA-2 and our climatology of MERRA-2 uncertainties as the covariance of the prior. Using ozonesonde observations from 2012 to 2017 at Summit Station, Greenland, the quality of the retrieved results is assessed. Comparisons show that retrieved partial columns reduce the bias of MERRA-2 ozone estimation below 10 km, and the average tropospheric ozone concentration is improved significantly.
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