A new TROPOMI product for tropospheric NO<sub>2</sub> columns over East Asia with explicit aerosol corrections
Mengyao LiuJintai LinHao KongK. F. BoersmaHenk EskesYugo KanayaQin HeXin TianKai QinPinhua XieRobert SpurrRuijing NiYingying YanHongjian WengJingxu Wang
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Abstract. We present a new product with explicit aerosol corrections, POMINO-TROPOMI, for tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) over East Asia, based on the newly launched TROPOspheric Monitoring Instrument with an unprecedented high horizontal resolution. Compared to the official TM5-MP-DOMINO (OFFLINE) product, POMINO-TROPOMI shows stronger concentration gradients near emission source locations and better agrees with MAX-DOAS measurements (R2=0.75; NMB=0.8 % versus R2=0.68, NMB=-41.9 %). Sensitivity tests suggest that implicit aerosol corrections, as in TM5-MP-DOMINO, lead to underestimations of NO2 columns by about 25 % over the polluted northern East China region. Reducing the horizontal resolution of a priori NO2 profiles would underestimate the retrieved NO2 columns over isolated city clusters in western China by 35 % but with overestimates of more than 50 % over many offshore coastal areas. The effect of a priori NO2 profiles is more important under calm conditions.Keywords:
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A two‐dimensional transport model constrained to measured surface CO 2 concentrations was used to simulate the spatial and temporal variation of CO 2 in the atmosphere for the period from 1975 to 2004. We find that the amplitude, phase and shape of the CO 2 seasonal cycle vary as a function of both altitude and latitude. Cross tropopause exchanges, especially the downward branch of the Brewer‐Dobson circulation, which brings stratospheric air to the upper troposphere at middle and high latitudes, change the CO 2 concentration and seasonal cycle in the extra‐tropics. The model results match recent aircraft measurements of CO 2 in the upper troposphere ( Matsueda et al. , 2002) remarkably well. We conclude that upper tropospheric CO 2 volume mixing ratios will provide a valuable tool for validating vertical transport. The implications of the CO 2 variation caused by the stratosphere‐troposphere exchange for remote sensing of CO 2 are discussed.
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<p>The stratosphere and troposphere are the main layers that define a significant part of the atmospheric processes of our planet. They are demarcated by the tropopause - a layer that has a stable stratification and makes it difficult to exchange air between them. As a consequence, the composition of the air differs slightly in the stratosphere and troposphere. However, the tropopause is not a fully material impermeable surface and therefore the exchange of impurities between both layers occurs. Under the conditions of a changing climate, the composition of the air in the troposphere has also noticeably changed. Therefore, it is important to study the processes of air exchange between the troposphere and stratosphere in a warming climate, especially if we take into account that one of the proposed geoengineering methods assumes to affect climate-forming factors by means of spraying sulphate particles into the stratosphere.</p><p>Here, we present the results of airborne measurements of the size distribution and chemical composition of aerosols carried out at the tropopause level and in the upper troposphere and lower stratosphere (UTLS) using the 'Optik' Tu-134 aircraft laboratory as a research platform. For the analysis, we have chosen 14 flight segments when the aircraft crossed the tropopause, which level was determined by the temperature gradient (up to 2&#176;C/ km). All the selected profiles of atmospheric constituents were measured over the Russian Arctic seas or coastal areas, since the tropopause in the northern latitudes is much lower than in the middle ones.</p><p>Significant differences in the elemental composition of aerosol particles were revealed in the UTLS. Si was dominated in the composition of stratospheric particles, and Fe or Al in the tropospheric ones. The ionic composition of the LS aerosols was predominantly represented by sulfates (SO<sub>4</sub><sup>2-</sup>), while tropospheric ones by a group of different ions.</p><p>The particle number size distributions (PNSD) in both UT and LS were dominated by the Aitken mode (20-50 nm). At the same time, there were some differences in PNSD &#8211; in the stratosphere, the distribution curve was shifted towards larger sizes that suggests the older age of particles measured there. It is also important to note that the nucleation mode particles (3&#8211;20 nm) were also detected during some flights in the lower stratosphere. This indicates that, despite the low humidity and the very low content of ammonia here, the processes of the new particle formation (NPF) in the stratosphere were taking place. Taking into account the dominance of SO<sub>4</sub><sup>2-</sup> in the ionic composition, one can be assumed that sulfuric acid played a dominant role in the lower stratospheric NPF.</p><p>This work was supported by the grant of the Ministry of Science and Higher Education of the Russian Federation (Agreement No 075-15-2021-934).</p>
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Upper tropospheric NO x controls, in part, the distribution of ozone in this greenhouse sensitive region of the atmosphere. Many factors control NO x in this region. As a result it is difficult to assess uncertainties in anthropogenic perturbations to NO from aircraft, for example, without understanding the role of the other major NO x sources in the upper troposphere. These include in situ sources (lightning, aircraft), convection from the surface (biomass burning, fossil fuels, soils), stratospheric intrusions, and photochemical recycling from HNO 3 . This work examines the separate contribution to upper tropospheric “primary” NO x from each source category and uses two different chemical transport models (CTMs) to represent a range of possible atmospheric transport. Because aircraft emissions are tied to particular pressure altitudes, it is important to understand whether those emissions are placed in the model stratosphere or troposphere and to assess whether the models can adequately differentiate stratospheric air from tropospheric air. We examine these issues by defining a point‐by‐point “tracer tropopause” in order to differentiate stratosphere from troposphere in terms of NO x perturbations. Both models predict similar zonal average peak enhancements of primary NO x due to aircraft (≈10–20 parts per trillion by volume (pptv) in both January and July); however, the placement of this peak is primarily in a region of large stratospheric influence in one model and centered near the level evaluated as the tracer tropopause in the second. Below the tracer tropopause, both models show negligible NO x derived directly from the stratospheric source. Also, they predict a typically low background of 1‐20 pptv NO x when tropospheric HNO 3 is constrained to be 100 pptv of HNO 3 . The two models calculate large differences in the total background NO x (defined as the source of NO x from lightning + stratosphere + surface + HNO 3 ) when using identical loss frequencies for NO x . This difference is primarily due to differing treatments of vertical transport. An improved diagnosis of this transport that is relevant to NO x requires either measurements of a surface‐based tracer with a substantially shorter lifetime than 222 Rn or diagnosis and mapping of tracer correlations with different source signatures. Because of differences in transport by the two models we cannot constrain the source of NO x from lightning through comparison of average model concentrations with observations of NO x .
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A three‐dimensional global chemistry transport model is used to examine the impact of stratosphere to troposphere fluxes of ozone (O 3 ) and nitric acid (HNO 3 ) on tropospheric chemistry. The stratospheric fluxes are parameterized as a tropospheric source of O 3 and HNO 3 . The accuracy of the resulting model simulation is compared with measurements. The tropospheric impact of the stratospheric fluxes is examined through a parallel simulation that includes no stratospheric fluxes of O 3 and HNO 3 . Stratosphere‐troposphere exchange (STE) increases the global average tropospheric ozone column by only 11.5%, increasing it in the Northern Hemisphere by 10.5% and in the Southern Hemisphere by 13%. STE shifts the springtime ozone maximum ∼1 month earlier in the Northern Hemisphere. The portion of the O 3 distribution of stratospheric origin in the troposphere increases with altitude, from a maximum of 10–20% in the lower troposphere to 40–50% in the upper troposphere. The sensitivity of the tropospheric response to the spatiotemporal distribution of STE is also examined. On a hemispheric and annual scale the tropospheric composition is particularly sensitive to the temporal distribution of STE. The separate roles of stratospheric fluxes of O 3 and HNO 3 are also identified.
Tropospheric ozone
Atmospheric chemistry
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The effect on the modeled chemical climatology of the upper troposphere and lower stratosphere of including a limited set of nonmethane hydrocarbons in a two‐dimensional (2‐D) zonal average model is presented. Recent measurements of nitrogenated and oxygenated hydrocarbons in the upper troposphere and lower stratosphere have revealed the possibility of significant perturbation of this region. A zonally averaged 2‐D chemical transport model enhanced to represent tropospheric processes was used to explore the extent of this perturbation on global and regional spatial scales and on seasonal and annual average timescales. Acetone was shown to cause a significant increase in the HO x budgets of the upper troposphere in the midlatitude Northern Hemisphere during the winter and early spring months, with acetone photolysis providing the most significant source of HO x radicals. The tropical upper troposphere has a uniform increase in HO x of up to 20% throughout the year because of acetone photolysis. Including the hydrocarbons caused a net increase in ozone of 5 ppbv in the lower and middle troposphere and 5–10 ppbv in the upper troposphere for global and annual averages. The effect of including the hydrocarbons on the calculated model ozone response for the case of doubled surface mixing ratios of atmospheric CH 4 is also discussed. It is shown that including hydrocarbons in the model has a significant effect on the modeled ozone response to the methane increase.
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Tropospheric ozone
Atmospheric chemistry
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A global two‐dimensional time‐dependent model has been used to estimate the tropospheric distributions of sulfur compounds resulting from natural emissions of H 2 S or DMS and from man‐made emissions of SO 2 . Comparisons of observations of H 2 S, DMS, SO 2 , and SO 4 − in remote areas with the model estimates indicate that the global flux of H 2 S and DMS, taken together, amounts to at most a few tens of Tg S yr −1 . The present man‐made emissions Of SO 2 (about 80 Tg S yr −1 ) can account for a dominant part of the SO 2 and SO 4 − observed in the lower troposphere of the northern hemisphere. On the other hand, neither natural emissions of H 2 S and DMS at the surface nor man‐made emissions of SO 2 seem to be able to explain the relatively high values of SO 2 observed in the middle and upper troposphere in both hemispheres. Our calculations indicate that a relatively long‐lived precursor must be involved as a source for this SO 2 . The amount of SO 2 produced by the oxidation of CS 2 and OCS does not seem sufficiently high. Average residence times in the atmosphere for H 2 S, SO 2 , and SO 4 − have been estimated to about 1, 1.5, and 5 days, respectively. If only higher portions of the troposphere are considered, the residence times increase considerably.
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This paper investigates the impact of circulation changes in a changed climate on the exchange of ozone between the stratosphere and the troposphere. We have identified an increase in the net transport of ozone into the troposphere in the future climate of 37%, although a decreased ozone lifetime means that the overall tropospheric burden decreases. There are regions in the midlatitudes to high latitudes where surface ozone is predicted to increase in the spring. However, these increases are not significant. Significant ozone increases are predicted in regions of the upper troposphere. The general increase in the stratospheric contribution (O 3 s tracer) to tropospheric ozone in the climate changed scenario indicates that the stratosphere will play an even more significant role in the future.
Tropospheric ozone
Middle latitudes
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