Search

Our understanding of the processes that control the burden and budget of tropospheric ozone have changed dramatically over the last 60 years. Models are the key tools used to understand these changes and these underscore that there are many processes important in controlling the tropospheric ozone budget. In this critical review we assess our evolving understanding of these processes, both physical and chemical. We review model simulations from the IGAC Atmospheric Chemistry and Climate Model Intercomparison Project and Chemistry Climate Modelling Initiative (CCMI) to assess the changes in the tropospheric ozone burden and its budget from 1850-2010. Analysis of these data indicates that there has been significant growth in the ozone burden from 1850-2000 (~ 43±9%), but smaller growth between 1960-2000 (~16±10%) and that the models simulate burdens of ozone well within recent satellite estimates. The CCMI model ozone budgets indicate that the net chemical production of ozone in the troposphere plateaued in the 1990s and has not changed since then inspite of increases in the burden. There has been a shift in net ozone production in the troposphere being greatest in the Northern mid and high latitudes to the Northern tropics; driven by the regional evolution of precursor emissions. An analysis of the evolution of tropospheric ozone through the 21st century, as simulated by CMIP5 models, reveals a large source of uncertainty associated with models themselves (i.e. in the way that they simulate the chemical and physical processes that control tropospheric ozone). This structural uncertainty is greatest in the near term (two to three decades) but emissions scenarios dominate uncertainty in the longer-term (2050-2100) evolution of tropospheric ozone. This intrinsic model uncertainty prevents robust predictions of near-term changes in the tropospheric ozone burden, and we review how progress can be made to reduce this limitation.

53 pags., 19 figs., 1 tab., Our understanding of the processes that control the burden and budget of tropospheric ozone has changed dramatically over the last 60 years. Models are the key tools used to understand these changes, and these underscore that there are many processes important in controlling the tropospheric ozone budget. In this critical review, we assess our evolving understanding of these processes, both physical and chemical. We review model simulations from the International Global Atmospheric Chemistry Atmospheric Chemistry and Climate Model Intercomparison Project and Chemistry Climate Modelling Initiative to assess the changes in the tropospheric ozone burden and its budget from 1850 to 2010. Analysis of these data indicates that there has been significant growth in the ozone burden from 1850 to 2000 (approximately 43 ± 9%) but smaller growth between 1960 and 2000 (approximately 16 ± 10%) and that the models simulate burdens of ozone well within recent satellite estimates. The Chemistry Climate Modelling Initiative model ozone budgets indicate that the net chemical production of ozone in the troposphere plateaued in the 1990s and has not changed since then inspite of increases in the burden. There has been a shift in net ozone production in the troposphere being greatest in the northern mid and high latitudes to the northern tropics, driven by the regional evolution of precursor emissions. An analysis of the evolution of tropospheric ozone through the 21st century, as simulated by Climate Model Intercomparison Project Phase 5 models, reveals a large source of uncertainty associated with models themselves (i.e., in the way that they simulate the chemical and physical processes that control tropospheric ozone). This structural uncertainty is greatest in the near term (two to three decades), but emissions scenarios dominate uncertainty in the longer term (2050¿2100) evolution of tropospheric ozone. This intrinsic model uncertainty prevents robust predictions of near-term changes in the tropospheric ozone burden, and we review how progress can be made to reduce this limitation., ATA and PTG would like to acknowledge support from National Centre for Atmospheric Science. YE would like to acknowledge support from the National Science Foundation Atmospheric and Geospace Sciences awards # 1900795 and 1929368. TW acknowledges support from the Hong Kong Research Grants Council (T24-504/17-N) and the National Natural Science Foundation of China (91844301). ASL thanks European Executive Agency under the European Union’s Horizon 2020 Research Innovation programme (Project “ERC-2016-COG 726349 CLIMAHAL”). RH is supported by an NERC Independent Research Fellowship (NE/N014375/1). YMS is supported by an NERC PhD studentship. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

gibt's hier nicht

We present vertical soundings (2005–2015) of tropospheric water vapor (H2O) and its D ∕ H isotope ratio (δD) derived from ground-based solar Fourier transform infrared (FTIR) measurements at Zugspitze (47° N, 11° E, 2964 m a.s.l.). Beside water vapor profiles with optimized vertical resolution (degrees of freedom for signal, DOFS, = 2.8), {H2O, δD} pairs with consistent vertical resolution (DOFS = 1.6 for H2O and δD) applied in this study. The integrated water vapor (IWV) trend of 2.4 [−5.8, 10.6] % decade−1 is statistically insignificant (95 % confidence interval). Under this caveat, the IWV trend estimate is conditionally consistent with the 2005–2015 temperature increase at Zugspitze (1.3 [0.5, 2.1] K decade−1), assuming constant relative humidity. Seasonal variations in free-tropospheric H2O and δD exhibit amplitudes of 140 and 50 % of the respective overall means. The minima (maxima) in January (July) are in agreement with changing sea surface temperature of the Atlantic Ocean. Using extensive backward-trajectory analysis, distinct moisture pathways are identified depending on observed δD levels: low column-based δD values (δDcol δD values (δDcol > 95th percentile: 46° N, 4.6 km). Backward-trajectory classification indicates that {H2O, δD} observations are influenced by three long-range-transport patterns towards Zugspitze assessed in previous studies: (i) intercontinental transport from North America (TUS; source region: 25–45° N, 70–110° W, 0–2 km altitude), (ii) intercontinental transport from northern Africa (TNA; source region: 15–30° N, 15° W–35° E, 0–2 km altitude), and (iii) stratospheric air intrusions (STIs; source region: > 20° N, above zonal mean tropopause). The FTIR data exhibit significantly differing signatures in free-tropospheric {H2O, δD} pairs (5 km a.s.l.) – given as the mean with uncertainty of ±2 standard error (SE) – for TUS (VMRH2O = 2.4 [2.3, 2.6] × 103 ppmv, δD = −315 [−326, −303] ‰), TNA (2.8 [2.6, 2.9] × 103 ppmv, −251 [−257, −246] ‰), and STIs (1.2 [1.1, 1.3] × 103 ppmv, −384 [−397, −372] ‰). For TUS events, {H2O, δD} observations depend on surface temperature in the source region and the degree of dehydration having occurred during updraft in warm conveyor belts. During TNA events (dry convection of boundary layer air) relatively moist and weakly HDO-depleted air masses are imported. In contrast, STI events are associated with import of predominantly dry and HDO-depleted air masses. These long-range-transport patterns potentially involve the import of various trace constituents to the central European free troposphere, i.e., import of pollution from North America (e.g., aerosol, ozone, carbon monoxide), Saharan mineral dust, stratospheric ozone, and other airborne species such as pollen. Our results provide evidence that {H2O, δD} observations are a valuable proxy for the transport of such tracers. To validate this finding, we consult a database of transport events (TNA and STI) covering 2013–2015 deduced by data filtering from in situ measurements at Zugspitze and lidar profiles at nearby Garmisch. Indeed, the FTIR data related to these verified TNA events (27 days) exhibit characteristic fingerprints in IWV (5.5 [4.9, 6.1] mm) and δDcol (−266 [−284, −247] ‰), which are significantly distinguishable from the rest of the time series (4.3 [4.1, 4.5] mm, −316 [−324, −308] ‰). This holds true for 136 STI days considering uncertainties of ±1 SE (4.2 [4.0, 4.3] mm, −322 [−327, −316] ‰) with respect to the remainder (4.6 [4.5, 4.8] mm, −302 [−307, −297] ‰). Furthermore, deep stratospheric intrusions to the Zugspitze summit (in situ humidity and beryllium-7 data filtering) show a significantly lower mean value (−334 [−337, −330] ‰) of lower-tropospheric δD (3–5 km a.s.l.) than the rest of the 2005–2015 time series (−284 [−286, −282] ‰) considering uncertainty of ±2 SE. Our results show that consistent {H2O, δD} observations at Zugspitze can serve as an operational indicator for long-range-transport events potentially affecting regional climate and air quality, as well as human health in central Europe.

International audience; Standardized definitions of vertical resolution and a standardized approach for the definition, propagation and reporting of uncertainty in the ozone lidar profiles contributing to the Network for the Detection for Atmospheric Composition Change (NDACC) database were recently developed.Two standardized definitions that describe homogeneously and unequivocally the impact of vertical filtering were recommended. The first definition is based on the width of the response to a Finite Impulse-type perturbation. The second definition relates to the cut-off frequency of a digital filter. Both definitions yield approximately the same values. Numerical tools (routines written in several programming languages) were developed and distributed to lidar investigators in order to implement these standardized definitions within the entire network NDACC, as well as across the tropospheric ozone network TOLNet.The proposed approach for the introduction and propagation of uncertainty in the NDACC ozone DIAL algorithms relies on the careful selection of independent uncertainty components propagated in parallel through the data processing chain before being combined together into an ozone combined standard uncertainty. The uncertainty sources contributing to the uncertainty budget include detection noise, saturation correction, background noise extraction, the absorption cross-sections of ozone, NO2, SO2, and O2, the molecular extinction cross-sections, and the number densities of the air, NO2, and SO2.The network-wide implementation of the proposed standardized definitions and approaches now allows a clear interpretation of the effective vertical resolution of lidar profiles when compared to profiles measured by other instruments/techniques, and allows a clear understanding and interpretation of the quality and limitations of the lidar measurements within NDACC and TOLNet. A review of these definitions and approaches and the implication for future data intercomparisons will be presented at the Symposium.

Interest in stratospheric aerosol and its role in climate have increased over the last decade due to the observed increase in stratospheric aerosol since 2000 and the potential for changes in the sulfur cycle induced by climate change. This review provides an overview about the advances in stratospheric aerosol research since the last comprehensive assessment of stratospheric aerosol was published in 2006. A crucial development since 2006 is the substantial improvement in the agreement between in situ and space-based inferences of stratospheric aerosol properties during volcanically quiescent periods. Furthermore, new measurement systems and techniques, both in situ and space based, have been developed for measuring physical aerosol properties with greater accuracy and for characterizing aerosol composition. However, these changes induce challenges to constructing a long-term stratospheric aerosol climatology. Currently, changes in stratospheric aerosol levels less than 20% cannot be confidently quantified. The volcanic signals tend to mask any nonvolcanically driven change, making them difficult to understand. While the role of carbonyl sulfide as a substantial and relatively constant source of stratospheric sulfur has been confirmed by new observations and model simulations, large uncertainties remain with respect to the contribution from anthropogenic sulfur dioxide emissions. New evidence has been provided that stratospheric aerosol can also contain small amounts of nonsulfate matter such as black carbon and organics. Chemistry-climate models have substantially increased in quantity and sophistication. In many models the implementation of stratospheric aerosol processes is coupled to radiation and/or stratospheric chemistry modules to account for relevant feedback processes.

In July 2013 very strong boreal fire plumes were observed at the northern rim of the Alps by lidar and ceilometer measurements of aerosol, ozone and water vapour for about three weeks. In addition, some of the lower-tropospheric components of these layers were analyzed at the Global Atmosphere Watch laboratory at the Schneefernerhaus high-altitude research station (2650 m a.s.l., located a few hundred metres south-west of the Zugspitze summit). The high amount of particles confirms our hypothesis that fires in the Arctic regions of North America have a much stronger impact on the Central European atmosphere than the multitude of fires in the United States. This has been ascribed to the prevailing anticyclonic advection pattern during favourable periods and subsidence, in contrast to warm-conveyor-belt export, rainout and dilution frequently found for lower latitudes. A high number of the pronounced aerosol structures were positively correlated with elevated ozone. Chemical ozone formation in boreal fire plumes is known to be rather limited. Indeed, these air masses could be attributed to stratospheric air intrusions over remote high latitude regions obviously picking up the aerosol on their way across Canada. In one case subsidence from the stratosphere over Siberia over as many as 15 to 20 days without increase in humidity was observed although a significant amount of Canadian smoke was trapped. These coherent air streams lead to rather straight and rapid transport of the particles to Europe.

Water vapor is the most important greenhouse gas and its spatio-temporal variability strongly exceeds that of all other greenhouse gases. However, this variability has hardly been studied quantitatively so far. We present an analysis of a five-year period of water vapor measurements in the free troposphere above Mt. Zugspitze (2962 m a.s.l., Germany). Our results are obtained from a combination of measurements of vertically integrated water vapor (IWV), recorded with a solar Fourier Transform InfraRed (FTIR) spectrometer on the summit of Mt. Zugspitze and of water vapor profiles recorded with the nearby differential absorption lidar (DIAL) at the Schneefernerhaus research station. The special geometrical arrangement of one zenith-viewing and one sun-pointing instrument and the temporal resolution of both instruments allow for an investigation of the spatio-temporal variability of IWV on a spatial scale of less than one kilometer and on a time scale of less than one hour. The SD of differences between both instruments σIWV calculated for varied subsets of data serves as a measure of variability. The different subsets are based on various spatial and temporal matching criteria. Within a time interval of 20 min, the spatial variability becomes significant for horizontal distances above 2 km, but only in the warm season (σIWV = 0.35 mm). However, it is not sensitive to the horizontal distance during the winter season. The variability of IWV within a time interval of 30 min peaks in July and August (σIWV > 0.55 mm, mean horizontal distance = 2.5 km and has its minimum around midwinter (σIWV < 0.2 mm, mean distance > 5 km). The temporal variability of IWV is derived by selecting subsets of data from both instruments with optimal volume matching. For a short time interval of 5 min, the variability is 0.05 mm and increases to more than 0.5 mm for a time interval of 15 h. The profile variability of water vapor is determined by analyzing subsets of water vapor profiles recorded by the DIAL within time intervals from 1 to 5 h. For all altitudes, the variability increases with widened time intervals. The lowest relative variability is observed in the lower free troposphere around an altitude of 4.5 km. Above 5 km, the relative variability increases continuously up to the tropopause by about a factor of 3. Analysis of the covariance of the vertical variability reveals an enhanced variability of water vapor in the upper troposphere above 6 km. It is attributed to a more coherent flow of heterogeneous air masses, while the variability at lower altitudes is also driven by local atmospheric dynamics. By studying the short-term variability of vertical water vapor profiles recorded within a day, we come to the conclusion that the contribution of long-range transport and the advection of heterogeneous layer structures may exceed the impact of local convection by one order of magnitude even in the altitude range between 3 and 5 km.

SRef-ID: 1607-7962/gra/EGU05-A-08329. Geophys. Res. Abstracts