scholarly journals Key chemical NO<sub>x</sub> sink uncertainties and how they influence top-down emissions of nitrogen oxides

2013 ◽  
Vol 13 (17) ◽  
pp. 9057-9082 ◽  
Author(s):  
T. Stavrakou ◽  
J.-F. Müller ◽  
K. F. Boersma ◽  
R. J. van der A ◽  
J. Kurokawa ◽  
...  
Keyword(s):  
South Asia ◽  
Transport Model ◽  
Field Studies ◽  
Anthropogenic Source ◽  
Oh Radicals ◽  
Top Down ◽  
Model Calculations ◽  
Tropical Regions ◽  
Recent Developments ◽  
The Impact

Abstract. Triggered by recent developments from laboratory and field studies regarding major NOx sink pathways in the troposphere, this study evaluates the influence of chemical uncertainties in NOx sinks for global NOx distributions calculated by the IMAGESv2 chemistry-transport model, and quantifies their significance for top-down NOx emission estimates. Our study focuses on five key chemical parameters believed to be of primary importance, more specifically, the rate of the reaction of NO2 with OH radicals, the newly identified HNO3-forming channel in the reaction of NO with HO2, the reactive uptake of N2O5 and HO2 by aerosols, and the regeneration of OH in the oxidation of isoprene. Sensitivity simulations are performed to estimate the impact of each source of uncertainty. The model calculations show that, although the NO2+OH reaction is the largest NOx sink globally accounting for ca. 60% of the total sink, the reactions contributing the most to the overall uncertainty are the formation of HNO3 in NO+HO2, leading to NOx column changes exceeding a factor of two over tropical regions, and the uptake of HO2 by aqueous aerosols, in particular over East and South Asia. Emission inversion experiments are carried out using model settings which either minimise (MINLOSS) or maximise (MAXLOSS) the total NOx sink, both constrained by one year of OMI NO2 column data from the DOMINO v2 KNMI algorithm. The choice of the model setup is found to have a major impact on the top-down flux estimates, with 75% higher emissions for MAXLOSS compared to the MINLOSS inversion globally. Even larger departures are found for soil NO (factor of 2) and lightning (1.8). The global anthropogenic source is better constrained (factor of 1.57) than the natural sources, except over South Asia where the combined uncertainty primarily associated to the NO+HO2 reaction in summer and HO2 uptake by aerosol in winter lead to top-down emission differences exceeding a factor of 2. Evaluation of the emission optimisation is performed against independent satellite observations from the SCIAMACHY sensor, with airborne NO2 measurements of the INTEX-A and INTEX-B campaigns, as well as with two new bottom-up inventories of anthropogenic emissions in Asia (REASv2) and China (MEIC). Neither the MINLOSS nor the MAXLOSS setup succeeds in providing the best possible match with all independent datasets. Whereas the minimum sink assumption leads to better agreement with aircraft NO2 profile measurements, consistent with the results of a previous analysis (Henderson et al., 2012), the same assumption leads to unrealistic features in the inferred distribution of emissions over China. Clearly, although our study addresses an important issue which was largely overlooked in previous inversion exercises, and demonstrates the strong influence of NOx loss uncertainties on top-down emission fluxes, additional processes need to be considered which could also influence the inferred source.

scholarly journals Key chemical NO<sub>x</sub> sink uncertainties and how they influence top-down emissions of nitrogen oxides

2013 ◽  
Vol 13 (3) ◽  
pp. 7871-7929 ◽  
Author(s):  
T. Stavrakou ◽  
J.-F. Müller ◽  
K. F. Boersma ◽  
R. J. van der A ◽  
J. Kurokawa ◽  
...  
Keyword(s):  
Transport Model ◽  
Field Studies ◽  
Anthropogenic Source ◽  
Oh Radicals ◽  
Top Down ◽  
Model Calculations ◽  
Tropical Regions ◽  
Emission Fluxes ◽  
Recent Developments ◽  
The Impact

Abstract. Triggered by recent developments from laboratory and field studies regarding major NOx sink pathways in the troposphere, this study evaluates the influence of chemical uncertainties in NOx sinks for global NOx distributions calculated by the IMAGESv2 chemistry-transport model, and quantifies their significance for top-down NOx emission estimates. Our study focuses on four key chemical parameters believed to be of primary importance, more specifically, the rate of the reaction of NO2 with OH radicals, the newly-identified HNO3-forming channel in the reaction of NO with HO2, the reactive uptake of N2O5 on aerosols, and the regeneration of OH in the oxidation of isoprene. Sensitivity simulations are performed to estimate the impact of each source of uncertainty. The model calculations show that, although the NO2 + OH reaction is the largest NOx sink globally accounting for 50–70% of the total sink, the reaction contributing the most to the overall uncertainty is the formation of HNO3 in NO + HO2, leading to NOx column changes reaching a~factor of two over tropical regions, and to a 35% decrease in the global tropospheric NOx lifetime. Emission inversion experiments are carried out using model settings which either miminize (MINLOSS) or maximize (MAXLOSS) the total NOx sink, both constrained by one year of OMI NO2 column data from the DOMINO v2 KNMI algorithm. The choice of the model setup is found to have a major impact on the top-down flux estimates, with 50% higher emissions for MAXLOSS compared to the MINLOSS inversion globally. Even larger departures are found for soil NO (factor of 2) and lightning (70%), whereas the global anthropogenic source is comparatively better constrained, especially in China. Evaluation of the emission optimization is performed against independent satellite observations from the SCIAMACHY sensor, airborne NO2 measurements, observed NOx lifetimes at megacities, as well as with two new bottom-up inventories of anthropogenic emissions in Asia (REASv2) and China (MEIC). Neither the MINLOSS nor the MAXLOSS setup succeeds in providing the best possible match with all independent datasets. Whereas the minimum sink assumption leads to better agreement with aircraft NO2 profile measurements, comforting the results of a previous analysis (Henderson et al., 2012), the same assumption leads to unrealistic features in the inferred distribution of emissions over China. Clearly, although our study addresses an important issue which was largely overlooked in previous inversion exercises, and demonstrates the strong influence of NOx loss uncertainties on top-down emission fluxes, additional processes need to be considered which could also influence the inferred source.

scholarly journals Influences of hydroxyl radicals (OH) on top-down estimates of the global and regional methane budgets

2020 ◽  
Author(s):  
Yuanhong Zhao ◽  
Marielle Saunois ◽  
Philippe Bousquet ◽  
Xin Lin ◽  
Antoine Berchet ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Climate Models ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Temporal Variations ◽  
Oh Radicals ◽  
Chemical Transport Model ◽  
Top Down ◽  
Ch4 Emissions ◽  
The Impact

Abstract. The hydroxyl radical (OH), which is the dominant sink of methane (CH4), plays a key role to close the global methane budget. Previous research that assessed the impact of OH changes on the CH4 budget mostly relied on box modeling inversions with a very simplified atmospheric transport and no representation of the heterogeneous spatial distribution of OH radicals. Here using a variational Bayesian inversion framework and a 3D chemical transport model, LMDz, combined with 10 different OH fields derived from chemistry-climate models (CCMI experiment), we evaluate the influence of OH burden, spatial distribution, and temporal variations on the global CH4 budget. The global tropospheric mean CH4-reaction-weighted [OH] ([OH]GM-CH4) ranges 10.3–16.3 × 105 molec cm−3 across 10 OH fields during the early 2000s, resulting in inversion-based global CH4 emissions between 518 and 757 Tg yr−1. The uncertainties in CH4 inversions induced by the different OH fields are comparable to, or even larger than the uncertainty typically given by bottom-up and top-down estimates. Based on the LMDz inversions, we estimate that a 1 %-increase in OH burden leads to an increase of 4 Tg yr−1 in the estimate of global methane emissions, which is about 25 % smaller than what is estimated by box-models. The uncertainties in emissions induced by OH are largest over South America, corresponding to large inter-model differences of [OH] in this region. From the early to the late 2000s, the optimized CH4 emissions increased by 21.9 ± 5.7 Tg yr−1 (16.6–30.0 Tg yr−1), of which ~ 25 % (on average) is contributed by −0.5 to +1.8 % increase in OH burden. If the CCMI models represent the OH trend properly over the 2000s, our results show that a higher increasing trend of CH4 emissions is needed to match the CH4 observations compared to the CH4 emission trend derived using constant OH. This study strengthens the importance to reach a better representation of OH burden and of OH spatial and temporal distributions to reduce the uncertainties on the global CH4 budget.

scholarly journals The impact of SCIAMACHY near-infrared instrument calibration on CH<sub>4</sub> and CO total columns

2005 ◽  
Vol 5 (9) ◽  
pp. 2369-2383 ◽  
Author(s):  
A. M. S. Gloudemans ◽  
H. Schrijver ◽  
Q. Kleipool ◽  
M. M. P. van den Broek ◽  
A. G. Straume ◽  
...  
Keyword(s):  
Near Infrared ◽  
Transport Model ◽  
Random Effect ◽  
Model Calculations ◽  
Instrument Calibration ◽  
The Dead ◽  
The Impact ◽  
Dark Signal ◽  
Orbital Variation ◽  
Good Agreement

Abstract. The near-infrared spectra measured with the SCIAMACHY instrument on board the ENVISAT satellite suffer from several instrument calibration problems. The effects of three important instrument calibration issues on the retrieved methane (CH4) and carbon monoxide (CO) total columns have been investigated: the effects of the growing ice layer on the near-infrared detectors, the effects of the orbital variation of the instrument dark signal, and the effects of the dead/bad detector pixels. Corrections for each of these instrument calibration issues have been defined. The retrieved CH4 and CO total columns including these corrections show good agreement with CO measurements from the MOPITT satellite instrument and with CH4 model calculations by the chemistry transport model TM3. Using a systematic approach, it is shown that all three instrument calibration issues have a significant effect on the retrieved CH4 and CO total columns. However, the impact on the CH4 total columns is more pronounced than for CO, because of its smaller variability. Results for three different wavelength ranges are compared and show good agreement. The growing ice layer and the orbital variation of the dark signal show a systematic, but time-dependent effect on the retrieved CH4 and CO total columns, whereas the effect of the dead/bad pixels is rather unpredictable: some dead pixels show a random effect, some more systematic, and others no effect at all. The importance of accurate corrections for each of these instrument calibration issues is illustrated using examples where inaccurate corrections lead to a wrong interpretation of the results.

scholarly journals A tropical West Pacific OH minimum and implications for stratospheric composition

2014 ◽  
Vol 14 (9) ◽  
pp. 4827-4841 ◽  
Author(s):  
M. Rex ◽  
I. Wohltmann ◽  
T. Ridder ◽  
R. Lehmann ◽  
K. Rosenlof ◽  
...  
Keyword(s):  
Transport Model ◽  
Source Region ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
The West ◽  
Model Calculations ◽  
West Pacific ◽  
Stratospheric Composition ◽  
The Impact

Abstract. Most of the short-lived biogenic and anthropogenic chemical species that are emitted into the atmosphere break down efficiently by reaction with OH and do not reach the stratosphere. Here we show the existence of a pronounced minimum in the tropospheric column of ozone over the West Pacific, the main source region for stratospheric air, and suggest a corresponding minimum of the tropospheric column of OH. This has the potential to amplify the impact of surface emissions on the stratospheric composition compared to the impact when assuming globally uniform OH conditions. Specifically, the role of emissions of biogenic halogenated species for the stratospheric halogen budget and the role of increasing emissions of SO2 in Southeast Asia or from minor volcanic eruptions for the increasing stratospheric aerosol loading need to be reassessed in light of these findings. This is also important since climate change will further modify OH abundances and emissions of halogenated species. Our study is based on ozone sonde measurements carried out during the TransBrom cruise with the RV Sonne roughly along 140–150° E in October 2009 and corroborating ozone and OH measurements from satellites, aircraft campaigns and FTIR instruments. Model calculations with the GEOS-Chem Chemistry and Transport Model (CTM) and the ATLAS CTM are used to simulate the tropospheric OH distribution over the West Pacific and the transport pathways to the stratosphere. The potential effect of the OH minimum on species transported into the stratosphere is shown via modeling the transport and chemistry of CH2Br2 and SO2.

scholarly journals The 2019 Methane Budget And Uncertainties At 1 Degree Resolution And Each Country Through Bayesian Integration Of GOSAT Total Column Methane Data And A Priori Inventory Estimates

2021 ◽  
Author(s):  
John Worden ◽  
Daniel Cusworth ◽  
Zhen Qu ◽  
Yi Yin ◽  
Yuzhong Zhang ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Transport Model ◽  
Systematic Errors ◽  
Top Down ◽  
Bayesian Algorithm ◽  
Bottom Up ◽  
Fire Emissions ◽  
Bayesian Integration ◽  
The Impact ◽  
Total Column

Abstract. We present 2019 global methane (CH4) emissions and uncertainties, by sector, at 1-degree and country-scale resolution based on a Bayesian integration of satellite data and inventories. Globally, we find that agricultural and fire emissions are 227 +/− 19 Tg CH4/yr, waste is 50 +/− 7 Tg CH4/yr , anthropogenic fossil emissions are 82 +/− 12 Tg CH4/yr, and natural wetland/aquatic emissions are 180 +/− 10 Tg CH4/yr. These estimates are intended as a pilot dataset for the Global Stock Take in support of the Paris Agreement. However, differences between the emissions reported here and widely-used bottom-up inventories should be used as a starting point for further research because of potential systematic errors of these satellite based emissions estimates. Calculation of emissions and uncertainties: We first apply a standard optimal estimation (OE) approach to quantify CH4 fluxes using Greenhouse Gases Observing Satellite (GOSAT) total column CH4 concentrations and the GEOS-Chem global chemistry transport model. Second, we use a new Bayesian algorithm that projects these posterior fluxes to emissions by sector to 1 degree and country-scale resolution. This algorithm can also quantify uncertainties from measurement as well as smoothing error, which is due to the spatial resolution of the top-down estimate combined with the assumed structure in the prior emission uncertainties. Detailed Results: We find that total emissions for approximately 58 countries can be resolved with this observing system based on the degrees-of-freedom for signal (DOFS) metric that can be calculated with our Bayesian flux estimation approach. We find the top five emitting countries (Brazil, China, India, Russia, USA) emit about half of the global anthropogenic budget, similar to our choice of prior emissions. However, posterior emissions for these countries are mostly from agriculture, waste and fires (~129 Tg CH4/yr) with ~45 Tg CH4/yr from fossil emissions, as compared to prior inventory estimates of ~88 and 60 Tg CH4/yr respectively, primarily because the satellite observed concentrations are larger than expected in regions with substantive livestock activity. Differences are outside of 1-sigma uncertainties between prior and posterior for Brazil, India, and Russia but are consistent for China and the USA. The new Bayesian algorithm to quantify emissions from fluxes also allows us to “swap priors” if better informed or alternative priors and/or their covariances are available for testing. For example, recent bottom-up literature supposes greatly increased values for wetland/aquatic as well as fossil emissions. Swapping in priors that reflect these increased emissions results in posterior wetland emissions or fossil emissions that are inconsistent (differences greater than calculated uncertainties) with these increased bottom-up estimates, primarily because constraints related to the methane sink only allow total emissions across all sectors of ~560 Tg CH4/yr and because the satellite based estimate well constrains the spatially distinct fossil and wetland emissions. Given that this observing system consisting of GOSAT data and the GEOS-Chem model can resolve much of the different sectoral and country-wide emissions, with ~402 DOFS for the whole globe, our results indicate additional research is needed to identify the causes of discrepancies between these top-down and bottom-up results for many of the emission sectors reported here. In particular, the impact of systematic errors in the methane retrievals and transport model employed should be assessed where differences exist. However, our results also suggest that significant attention must be provided to the location and magnitude of emissions used for priors in top-down inversions; for example, poorly characterized prior emissions in one region and/or sector can affect top-down estimates in another because of the limited spatial resolution of these top-down estimates. Satellites such as the Tropospheric Monitoring Instrument (TROPOMI) and those in formulation such as the Copernicus CO2M, Methane-Sat, or Carbon Mapper offer the promise of much higher resolution fluxes relative to GOSAT assuming they can provide data with comparable or better accuracy, thus potentially reducing this uncertainty from poorly characterized emissions. These higher resolution estimates can therefore greatly improve the accuracy of emissions by reducing smoothing error. Fluxes calculated from other sources can also in principal be incorporated in the Bayesian estimation framework demonstrated here for the purpose of reducing uncertainty and improving the spatial resolution and sectoral attribution of subsequent methane emissions estimates.

scholarly journals Impact of International Shipping Emissions on Ozone and PM<sub>2.5</sub>: The Important Role of HONO and ClNO<sub>2</sub>

2021 ◽  
Author(s):  
Jianing Dai ◽  
Tao Wang
Keyword(s):  
Particulate Matter ◽  
Marine Boundary Layer ◽  
Transport Model ◽  
Fine Particulate Matter ◽  
Oxidative Capacity ◽  
Oh Radicals ◽  
Ship Emissions ◽  
Secondary Pollutants ◽  
Marine Areas ◽  
The Impact

Abstract. Ocean-going ships emit large amounts of air pollutants such as nitrogen oxide (NOx) and particulate matter. Ship-released NOx can be converted to nitrous acid (HONO) and nitryl chloride (ClNO2), which produce hydroxyl (OH) and chlorine (Cl) radicals and recycle NOx, thus affecting the oxidative capacity and production of secondary pollutants. However, these effects have not been quantified in previous investigations of the impacts of ship emissions. In this study, a regional transport model (WRF–Chem) revised to incorporate the latest HONO and ClNO2 processes was used to investigate their effects on the concentrations of ROx (RO2+HO2+OH) radicals, O3, and fine particulate matter (PM2.5) in Asia during summer. The results show that the ship-derived HONO and ClNO2 increased the concentration of ROx radicals by approximately two to three times in the marine boundary layer. The enhanced radicals then increased the O3 and PM2.5 concentrations in marine areas, with the ship contributions increasing from 9 % to 21 % and from 7 % to 10 %, respectively. The largest ROx enhancement was simulated over the remote ocean with the ship contribution increasing from 29 % to 50 %, which led to increases in ship-contributed O3 and PM2.5 from 21 % to 38 % and from 13 % to 19 %, respectively. In coastal cities, the enhanced levels of radicals also increased the maximum O3 and averaged PM2.5 concentrations from 5 % to 11 % and from 4 % to 8 % to 4 % to 12 %, respectively. These findings indicate that modeling studies without considering HONO and ClNO2 can significantly underestimate the impact of ship emissions on radicals and secondary pollutants. It is therefore important that these nitrogen compounds be included in future models of the impact of ship emissions on air quality.

scholarly journals Modeling lightning-NO<sub><i>x</i></sub> chemistry at sub-grid scale in a global chemical transport model

2015 ◽  
Vol 15 (23) ◽  
pp. 34091-34147 ◽  
Author(s):  
A. Gressent ◽  
B. Sauvage ◽  
D. Cariolle ◽  
M. Evans ◽  
M. Leriche ◽  
...  
Keyword(s):  
Large Scale ◽  
Transport Model ◽  
Chemical Transport ◽  
Horizontal Resolution ◽  
Parameter Estimates ◽  
Plume Dispersion ◽  
Chemical Transport Model ◽  
Tropical Regions ◽  
The Impact ◽  
Lightning Nox

Abstract. For the first time, a plume-in-grid approach is implemented in a chemical transport model (CTM) to parameterize the effects of the non-linear reactions occurring within high concentrated NOx plumes from lightning NOx emissions (LNOx) in the upper troposphere. It is characterized by a set of parameters including the plume lifetime, the effective reaction rate constant related to NOx-O3 chemical interactions and the fractions of NOx conversion into HNO3 within the plume. Parameter estimates were made using the DSMACC chemical box model, simple plume dispersion simulations and the mesoscale 3-D Meso-NH model. In order to assess the impact of the LNOx plume approach on the NOx and O3 distributions at large scale, simulations for the year 2006 were performed using the GEOS-Chem global model with a horizontal resolution of 2° × 2.5°. The implementation of the LNOx parameterization implies NOx and O3 decrease at large scale over the region characterized by a strong lightning activity (up to 25 and 8 %, respectively, over Central Africa in July) and a relative increase downwind of LNOx emissions (up to 18 and 2 % for NOx and O3, respectively, in July) are derived. The calculated variability of NOx and O3 mixing ratios around the mean value according to the known uncertainties on the parameter estimates is maximum over continental tropical regions with ΔNOx [−33.1; +29.7] ppt and ΔO3 [−1.56; +2.16] ppb, in January, and ΔNOx [−14.3; +21] ppt and ΔO3 [−1.18; +1.93] ppb, in July, mainly depending on the determination of the diffusion properties of the atmosphere and the initial NO mixing ratio injected by lightning. This approach allows (i) to reproduce a more realistic lightning NOx chemistry leading to better NOx and O3 distributions at the large scale and (ii) focus on other improvements to reduce remaining uncertainties from processes related to NOx chemistry in CTM.

Assessment of the impact of large changes in the ratio of photolysis rate of nitrate to that of gas nitric acid on HONO concentrations simulated by a 3-D chemical transport model

2021 ◽  
Author(s):  
Yitian Guo ◽  
Junling An ◽  
Jingwei Zhang
Keyword(s):  
Nitric Acid ◽  
Transport Model ◽  
Heterogeneous Reaction ◽  
Ground Surface ◽  
Chemical Transport ◽  
Field Studies ◽  
Chemical Transport Model ◽  
Substantial Impact ◽  
Photolysis Rate ◽  
The Impact

&lt;p&gt;Some studies show that photolysis of nitrate and deposited nitrate and gas nitric acid (HNO&lt;sub&gt;3&lt;/sub&gt;) on the ground surface is much faster than that of HNO&lt;sub&gt;3&lt;/sub&gt;. The former mechanism has been considered as a possible daytime HONO source and discussed in many laboratory and field studies. Although this mechanism is also coupled into some three-dimensional chemical transport models, the effect of large changes in the ratio of photolysis rate of nitrate to that of HNO&lt;sub&gt;3&lt;/sub&gt; (RAT) on HONO concentrations has not been assessed and will be discussed here by using the updated WRF-Chem model. Simulations indicate that in the morning, this mechanism only resulted in a HONO increase of a few ppt, while the heterogeneous reaction of NO&lt;sub&gt;2&lt;/sub&gt; enhanced HONO by about 150 ppt; in the afternoon, however, this mechanism led to a significant HONO increase, with its contribution to HONO concentrations being close to the contribution of the heterogeneous reaction of NO&lt;sub&gt;2&lt;/sub&gt;. In some heavily nitrate-polluted areas, this mechanism contributed more than 80% of HONO concentrations during the afternoon. Large changes in RAT produced a substantial impact on HONO concentrations. When RAT was altered from 15 to 100, increase of HONO concentrations was enhanced by about 6 times. Our results suggest that more laboratory and field studies on the photolysis rates of nitrate and deposited nitrate and HNO&lt;sub&gt;3&lt;/sub&gt; on the ground surface are still needed.&lt;/p&gt;

scholarly journals The impact of transport model differences on CO<sub>2</sub> surface flux estimates from OCO-2 retrievals of column average CO<sub>2</sub>

2018 ◽  
Vol 18 (10) ◽  
pp. 7189-7215 ◽  
Author(s):  
Sourish Basu ◽  
David F. Baker ◽  
Frédéric Chevallier ◽  
Prabir K. Patra ◽  
Junjie Liu ◽  
...  
Keyword(s):  
Transport Model ◽  
Co2 Flux ◽  
Surface Flux ◽  
Transport Models ◽  
Near Surface ◽  
Tropical Regions ◽  
Spatial Coverage ◽  
Global Transport ◽  
The Impact

Abstract. We estimate the uncertainty of CO2 flux estimates in atmospheric inversions stemming from differences between different global transport models. Using a set of observing system simulation experiments (OSSEs), we estimate this uncertainty as represented by the spread between five different state-of-the-art global transport models (ACTM, LMDZ, GEOS-Chem, PCTM and TM5), for both traditional in situ CO2 inversions and inversions of XCO2 estimates from the Orbiting Carbon Observatory 2 (OCO-2). We find that, in the absence of relative biases between in situ CO2 and OCO-2 XCO2, OCO-2 estimates of terrestrial flux for TRANSCOM-scale land regions can be more robust to transport model differences than corresponding in situ CO2 inversions. This is due to a combination of the increased spatial coverage of OCO-2 samples and the total column nature of OCO-2 estimates. We separate the two effects by constructing hypothetical in situ networks with the coverage of OCO-2 but with only near-surface samples. We also find that the transport-driven uncertainty in fluxes is comparable between well-sampled northern temperate regions and poorly sampled tropical regions. Furthermore, we find that spatiotemporal differences in sampling, such as between OCO-2 land and ocean soundings, coupled with imperfect transport, can produce differences in flux estimates that are larger than flux uncertainties due to transport model differences. This highlights the need for sampling with as complete a spatial and temporal coverage as possible (e.g., using both land and ocean retrievals together for OCO-2) to minimize the impact of selective sampling. Finally, our annual and monthly estimates of transport-driven uncertainties can be used to evaluate the robustness of conclusions drawn from real OCO-2 and in situ CO2 inversions.

scholarly journals The impact of SCIAMACHY near-infrared instrument calibration on CH<sub>4</sub> and CO total columns

2005 ◽  
Vol 5 (2) ◽  
pp. 1733-1770 ◽  
Author(s):  
A. M. S. Gloudemans ◽  
H. Schrijver ◽  
Q. Kleipool ◽  
M. M. P. van den Broek ◽  
A. G. Straume ◽  
...  
Keyword(s):  
Near Infrared ◽  
Transport Model ◽  
Random Effect ◽  
Model Calculations ◽  
Instrument Calibration ◽  
The Dead ◽  
The Impact ◽  
Dark Signal ◽  
Orbital Variation ◽  
Good Agreement

Abstract. The effects of three important SCIAMACHY near-infrared instrument calibration issues on the retrieved methane (CH4) and carbon monoxide (CO) total columns have been investigated: the effects of the growing ice layer on the near-infrared detectors, the effects of the orbital variation of the instrument dark signal, and the effects of the dead/bad detector pixels. Corrections for each of these instrument calibration issues have been defined. The retrieved CH4 and CO total columns including these corrections show good agreement with CO measurements from the MOPITT satellite instrument and with CH4 model calculations by the chemistry transport model TM3. Using a systematic approach, it is shown that all three instrument calibration issues have a significant effect on the retrieved CH4 and CO total columns, although the impact on the CH4 total columns is more pronounced than for CO. Results for three different wavelength ranges are compared and show good agreement. The growing ice layer and the orbital variation of the dark signal show a systematic, but time-dependent effect on the retrieved CH4 and CO total columns, whereas the dead/bad pixels show a more random effect. The importance of accurate corrections for each of these instrument calibration issues is illustrated using examples where inaccurate corrections lead to a wrong interpretation of the results.

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