Decreasing emissions of NOx relative to CO2 in East Asia inferred from satellite observations
Maximilian ReuterMichael BuchwitzAndreas HilbollAndreas RichterOliver SchneisingM. HilkerJ. HeymannH. BovensmannJohn P. Burrows
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Emission inventory
Chemical Transport Model
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One of the most important minor species in the atmosphere is nitrogen dioxide (NO2). The primary objective of the presented research was to propose a method to adjust emission inventories (emission fluxes) using tropospheric NO2 columns observed by OMI and SCIAMACHY instruments. Modified emission fluxes were used in a chemical weather model GEM-AQ. The GEM-AQ model results were compared with the monthly averaged satellite-derived column amount of NO2 over Europe for the 2008–2010 observing period. It was shown that the observed and modelled spatial distribution of high values of the NO2 column is highly correlated with the distribution of major anthropogenic sources in the modelling domain. The presented findings highlight the importance of the anthropogenic sources in the overall budget of NO2 in the polluted troposphere. Regions for which modelling results showed underestimation or overestimation compared with observations were constant for the whole analysis period. Thus, the NO2 column observations could be used for correcting emission estimates. The proposed emission correction method is based on the differences in modelled and satellite-derived NO2 columns. Modelling was done for 2011 using the original and adjusted emission inventories and compared with observed NO2 columns. The analysis was extended to compare modelling results with surface NO2 observations from selected air quality stations in Poland. A significant improvement in modelling results was obtained over regions with large overestimations in the control run for which the original emission fluxes were used.
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Emission inventory
Nitrogen dioxide
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SCIAMACHY
Emission inventory
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Abstract. A data assimilation system has been developed to estimate global nitrogen oxides (NOx) emissions using OMI tropospheric NO2 columns (DOMINO product) and a global chemical transport model (CTM), CHASER. The data assimilation system, based on an ensemble Kalman filter approach, was applied to optimize daily NOx emissions with a horizontal resolution of 2.8° during the years 2005 and 2006. The background error covariance estimated from the ensemble CTM forecasts explicitly represents non-direct relationships between the emissions and tropospheric columns caused by atmospheric transport and chemical processes. In comparison to the a priori emissions based on bottom-up inventories, the optimized emissions were higher over Eastern China, the Eastern United States, Southern Africa, and Central-Western Europe, suggesting that the anthropogenic emissions are mostly underestimated in the inventories. In addition, the seasonality of the estimated emissions differed from that of the a priori emission over several biomass burning regions, with a large increase over Southeast Asia in April and over South America in October. The data assimilation results were validated against independent data: SCIAMACHY tropospheric NO2 columns and vertical NO2 profiles obtained from aircraft and lidar measurements. The emission correction greatly improved the agreement between the simulated and observed NO2 fields; this implies that the data assimilation system efficiently derives NOx emissions from concentration observations. We also demonstrated that biases in the satellite retrieval and model settings used in the data assimilation largely affect the magnitude of estimated emissions. These dependences should be carefully considered for better understanding NOx sources from top-down approaches.
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Chemical Transport Model
Emission inventory
Microwave Limb Sounder
Seasonality
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Measurements of important reactive nitrogen species (NO, NO 2 , HNO 3 , PAN, PPN, NO 3 − , NO y ), C 1 to C 6 hydrocarbons, O 3 , chemical tracers (C 2 Cl 4 , CO), and meteorological parameters were made in the troposphere (0 to 12 km) over the western Pacific (0°–50°N) during the Pacific Exploratory Mission‐West A campaign (September–October 1991). Under clean conditions, mixing ratios of NO, NO 2 , NO y , and O 3 increased with altitude and showed a distinct latitudinal gradient. PAN showed a midtropospheric maximum, while nitric acid mixing ratios were generally highest near the surface. Measured NO y concentrations were significantly greater than the sum of individually measured nitrogen species (mainly NO x , PAN, and HNO 3 ), suggesting that a large fraction of reactive nitrogen present in the atmosphere is made up of hitherto unknown species. This shortfall was larger in the tropics (≈65%) compared to midlatitudes (≈40%) and was minimal in air masses with high HNO 3 mixing ratios (>100 ppt). A global three‐dimensional photochemical model has been used to compare observations with predictions and to assess the significance of major sources. It is possible that the tropical lightning source is much greater than commonly assumed, and both lightning source and its distribution remain a major area of uncertainty in the budgets of NO y and NO x . A large disagreement between measurement and theory exists in the atmospheric distribution of HNO 3 . It appears that surface‐based anthropogenic emissions provide nearly 65% of the global atmospheric NO y reservoir. Relatively constant NO x /NO y ratios imply that NO y and NO x are in chemical equilibrium and the NO y reservoir may be an important in situ source of atmospheric NO x . Data are interpreted to suggest that only about 20% of the upper tropospheric (7–12 km) NO x is directly attributable to its surface NO x source, and free tropospheric sources are dominant. In situ release of NO x from the NO y reservoir, lightning, direct transport of surface NO x , aircraft emissions, and small stratospheric input collectively maintain the NO x balance in the atmosphere. It is shown that atmospheric ratios of reactive nitrogen and sulfur species, along with trajectory analysis, can be used to pinpoint the source of Asian continental outflow. Compared to rural atmospheres over North America, air masses over the Pacific are highly efficient in net O 3 production. Sources of tropospheric NO x cannot yet be accurately defined due to shortcomings in measurements and theory.
Reactive nitrogen
Mixing ratio
Chemical Transport Model
Peroxyacetyl nitrate
Middle latitudes
Tropospheric ozone
Atmospheric chemistry
Lightning
Nitrogen dioxide
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We use observations from two aircraft during the ICARTT campaign over the eastern United States and North Atlantic during summer 2004, interpreted with a global 3‐D model of tropospheric chemistry (GEOS‐Chem) to test current understanding of regional sources, chemical evolution, and export of NO x . The boundary layer NO x data provide top‐down verification of a 50% decrease in power plant and industry NO x emissions over the eastern United States between 1999 and 2004. Observed NO x concentrations at 8–12 km altitude were 0.55 ± 0.36 ppbv, much larger than in previous U.S. aircraft campaigns (ELCHEM, SUCCESS, SONEX) though consistent with data from the NOXAR program aboard commercial aircraft. We show that regional lightning is the dominant source of this upper tropospheric NO x and increases upper tropospheric ozone by 10 ppbv. Simulating ICARTT upper tropospheric NO x observations with GEOS‐Chem requires a factor of 4 increase in modeled NO x yield per flash (to 500 mol/flash). Observed OH concentrations were a factor of 2 lower than can be explained from current photochemical models, for reasons that are unclear. A NO y ‐CO correlation analysis of the fraction f of North American NO x emissions vented to the free troposphere as NO y (sum of NO x and its oxidation products) shows observed f = 16 ± 10% and modeled f = 14 ± 9%, consistent with previous studies. Export to the lower free troposphere is mostly HNO 3 but at higher altitudes is mostly PAN. The model successfully simulates NO y export efficiency and speciation, supporting previous model estimates of a large U.S. anthropogenic contribution to global tropospheric ozone through PAN export.
Chemical Transport Model
Lightning
Outflow
Tropospheric ozone
Atmospheric chemistry
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The origin of NO x in the upper troposphere over the central United States is examined using aircraft observations obtained during the SUCCESS campaign in April–May of 1996. Correlations between NO y (sum of NO x and its oxidation products) and CO at 8–12 km altitude indicate that NO x originates primarily from convective transport of polluted boundary layer air. Lightning and aircraft emissions appear to be only minor sources of NO x . Chemical steady state model calculations constrained by local observations of NO underestimate the measured NO x /NO y concentration ratio at 8–12 km altitude by a factor of two on average. The magnitude of the underestimate is correlated with concentrations of condensation nuclei, which we take as a proxy for the age of air in the upper troposphere. We conclude that the NO x /NO y ratio is maintained above chemical steady state by frequent convective injections of fresh NO x from the polluted boundary layer and by the long lifetime of NO x in the upper troposphere (5–10 days). In contrast to previous studies, we find no evidence for fast heterogeneous recycling from HNO 3 to NO x in the upper troposphere.
Chemical Transport Model
Tropopause
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The global distribution of NO x in the troposphere is calculated using a simple three‐dimensional chemical tracer model. This model includes a simplified chemistry scheme for the tracers NO x ≡ NO + NO 2 and HNO 3 , which are redistributed by advection, dry and wet convection, and large‐scale diffusion. The sources of NO x considered are fossil fuel combustion, emissions from soil microbial activity, biomass burning, lightning discharges, emissions by aircraft, and downward transport from the stratosphere. Dry and wet deposition act as final sinks. At northern middle and high latitudes the calculated tropospheric NO x content is dominated by the surface sources, fossil fuel combustion in particular. In the tropical free troposphere, lightning discharges provide about 80% of the total NO x throughout the year. The zonally averaged fractional contribution of aircraft emissions strongly depends on the season. The largest contribution of this source, over 60%, occurs during January in the upper troposphere between 45°N and 60°N. The NO mixing ratios determined by the model show good overall agreement with vertical profiles measured during the Stratospheric Ozone Experiment (STRATOZ) III aircraft campaign.
TRACER
Chemical Transport Model
Mixing ratio
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Peroxyacetyl nitrate
Atmospheric chemistry
Nitrogen oxides
Chemical Transport Model
Mixing ratio
Tropospheric ozone
Emission inventory
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Chemical Transport Model
Lightning
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Abstract. Satellite observations of the tropospheric NO2 vertical column density (VCD) are closely correlated to surface NOx emissions and can thus be used to estimate the latter. In this study, the NO2 VCDs simulated by a regional chemical transport model with data from the updated Regional Emission inventory in ASia (REAS) version 2.1 were validated by comparison with multi-satellite observations (GOME, SCIAMACHY, GOME-2, and OMI) between 2000 and 2010. Rapid growth in NO2 VCD driven by expansion of anthropogenic NOx emissions was revealed above the central eastern China region, except during the economic downturn. In contrast, slightly decreasing trends were captured above Japan. The modeled NO2 VCDs using the updated REAS emissions reasonably reproduced the annual trends observed by multi-satellites, suggesting that the NOx emissions growth rate estimated by the updated inventory is robust. On the basis of the close linear relationship of modeled NO2 VCD, observed NO2 VCD, and anthropogenic NOx emissions, the NOx emissions in 2009 and 2010 were estimated. It was estimated that the NOx emissions from anthropogenic sources in China beyond doubled between 2000 and 2010, reflecting the strong growth of anthropogenic emissions in China with the rapid recovery from the economic downturn during late 2008 and mid-2009.
SCIAMACHY
Emission inventory
Chemical Transport Model
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