Quantifying Stratospheric Ozone in the Upper Troposphere with in Situ Measurements of HCl (original) (raw)
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Quantifying Stratospheric Ozone in the Upper Troposphere Using in Situ Measurements of HCl
Agu Fall Meeting Abstracts, 2003
A chemical ionization mass spectrometry (CIMS) technique has been developed for precise in situ measurements of hydrochloric acid (HCl). Aircraft measurements of HCl, ozone, and other gases were made in the summer of 2002 at subtropical latitudes in the upper troposphere and lower stratosphere. Significant abundances of HCl were found in many upper tropospheric air parcels as a result of stratosphere-to-troposphere transport. Minimum upper tropospheric HCl abundances are much lower than model mean estimates. Using the compact linear correlation of HCl with ozone in the lower stratosphere, the amount of stratospheric ozone in the upper troposphere can be uniquely distinguished from ozone that originated in the troposphere. This approach allows the processes affecting stratosphere to troposphere transport to be diagnosed in the atmosphere with greatly increased precision and accuracy.
Atmospheric Chemistry and Physics, 2013
Solar spectral fluxes (or irradiance) measured by the SOlar Radiation and Climate Experiment (SORCE) show different variability at ultraviolet (UV) wavelengths compared to other irradiance measurements and models (e.g. NRL-SSI, SATIRE-S). Some modelling studies have suggested that stratospheric/lower mesospheric O 3 changes during solar cycle 23 (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) can only be reproduced if SORCE solar fluxes are used. We have used a 3-D chemical transport model (CTM), forced by meteorology from the European Centre for Medium-Range Weather Forecasts (ECMWF), to simulate middle atmospheric O 3 using three different solar flux data sets (SORCE, NRL-SSI and SATIRE-S). Simulated O 3 changes are compared with Microwave Limb Sounder (MLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite data. Modelled O 3 anomalies from all solar flux data sets show good agreement with the observations, despite the different flux variations. The off-line CTM reproduces these changes through dynamical information contained in the analyses. A notable feature during this period is a robust positive solar signal in the tropical middle stratosphere, which is due to realistic dynamical changes in our simulations. Ozone changes in the lower mesosphere cannot be used to discriminate between solar flux data sets due to large uncertainties and the short time span of the observations. Overall this study suggests that, in a CTM, the UV variations detected by SORCE are not necessary to reproduce observed stratospheric O 3 changes during 2001-2010.
Attribution of stratospheric ozone trends to chemistry and transport: a modelling study
Atmospheric Chemistry and Physics, 2010
The decrease of the concentration of ozone depleting substances (ODS) in the stratosphere over the past decade raises the question to what extent observed changes in stratospheric ozone over this period are consistent with known changes in chemical composition and possible changes in atmospheric transport. Here we present a series 5 of ozone sensitivity calculations with a stratospheric chemistry transport model (CTM) driven with meteorological reanalyses from the European Centre for Medium Range Weather Forecast, covering the period 1978-2009. In order to account for the reversal in ODS trends, ozone trends are analysed in two periods, 1979-1999 and 2000-2009. Effects of ODS changes on the ozone chemistry are either accounted for or left out, 10 allowing for a distinct attribution of ozone trends to the different factors of variability, namely ODS acting via gas phase chemistry, ODS acting via polar heterogeneous chemistry, and changes in transport and temperature. Modeled column ozone trends are in excellent agreement with observed trends from the Total Ozone Mapping Spectrometer (TOMS) and Solar Backscatter UV (SBUV/2) as well as the Global Ozone
Journal of Geophysical Research, 1995
We present results of global tropospheric chemistry simulations with the coupled chemistry/atmospheric general circulation model ECHAM. Ultimately, the model will be used to study climate changes induced by anthropogenic influences on the chemistry of the atmosphere; meteorological parameters that are important for the chemistry, such as temperature, humidity, air motions, cloud and rain characteristics, and mixing processes are calculated on-line. The chemical part of the model describes background tropospheric CH4-CO-NOx-HOx photochemistry. Emissions of NO and CO, surface concentrations of CH4, and stratospheric concentrations of 03 and NOy are prescribed as boundary conditions. Calculations of the tropospheric 03 budget indicate that seasonal variabilities of the photochemical production and of injection from the stratosphere are represented realistically, although some aspects of the model still need improvement. Comparisons of calculated 03 surface concentrations and 03 profiles with available measurements show that the model reproduces 03 distributions in remote tropical and midlatitudinal sites. Also, the model matches typical profiles connected with deep convection in the Intertropical Convergence Zone (ITCZ). However, the model tends to underestimate 0 3 concentrations at the poles and in relatively polluted regions. These underestimates are caused by the poor representation of tropopause foldings in midlatitudes, which form a significant source of tropospheric 03 from the stratosphere, too weak transport to the poles, and the neglect of higher hydrocarbon chemistry. Also, mixing of polluted continental boundary layer air into the free troposphere may be underestimated. We discuss how these model deficiencies will be improved in the future. 20,983 20,984 ROELOFS AND LELIEVELD: TROPOSPHERIC O3 IN A CHEMISTRY GCM Institute for Meteorology in Hamburg, Germany [Roeckner et al. , 1992]. All meteorological data needed to evaluate chemical tracer concentrations in the atmosphere are calculated on-line by ECHAM with a time resolution of 40 min. As a result of the meteorology calculations, more CPU time is required than with an off-line model with the same spatial resolution and chemistry. In our model the calculations associated with chemical species (i.e., the processes described in section 2 and transport in the atmosphere) need approximately the same amount of CPU time as the meteorology calculations. However, the use of an off-line model requires substantial CPU time and memory to read and store data for the calculation of transport and the complex interactions between meteorological and chemical processes, whereas a large amount of data may be needed to cover different model resolutions. Further, a chemistry GCM interactively calculates concentrations of radiatively active species such as 03 that directly drive the radiation scheme and the GCM meteorology. When fully developed and tested, a coupled chemistry GCM is a powerful tool in the study of the intricate interactions between atmospheric chemistry and global climate.
Atmospheric Environment, 2011
Stratosphericetropospheric exchange (STE) processes contribute at both high and low-elevation monitoring sites to background ozone (O 3) concentrations. This study addresses the importance of stratospheric intrusions contributing to enhanced hourly average surface O 3 concentrations (i.e., !50 ppb) at 12 O 3 monitoring stations in the western and northern tier of the US for 2006, 2007, and 2008. The Lagrangian Analysis Tool (LAGRANTO) trajectory model identified specific days when stratosphere-to-troposphere transport was optimal to elevate surface O 3 levels. The coincidences between the number of days with a daily maximum hourly average O 3 concentration ! 50 ppb and stratosphere-to-troposphere transport to surface (STT-S > 0) were quantified. The high-elevation site at Yellowstone National Park (NP) in Wyoming exhibited the most coincidences (i.e., more than 19 days a month) during the spring and summer for hourly average O 3 concentrations ! 50 ppb with STT-S > 0 of the 12 monitoring sites. At this site, the daily maximum hourly springtime average O 3 concentrations were usually in the 60e70 ppb range. The maximum daily 8-h average concentrations mostly ranged from 50 to 65 ppb. At many of the lowerelevation sites, there was a preference for O 3 enhancements to be coincident with STT-S > 0 during the springtime, although summertime occurrences were sometimes observed. When statistically significant coincidences occurred, the daily maximum hourly average concentrations were mostly in the 50e65 ppb range and the daily maximum 8-h average concentrations were usually in the 50e62 ppb range. For many cases, the coincidences between the enhancements and the STT-S events occurred over a continuous multiday period. Supplementary observations, such as (1) the greater frequency of O 3 concentration enhancements occurring during the springtime versus other times of the year, (2) the elevation dependency of the frequency of enhancements, (3) the year-to-year variability, (4) the timing of the hour-byhour occurrences of the O 3 concentration enhancements within and across monitoring sites, and (5) the detailed analyses of O 3 enhancement events at specific sites, provide additional support for our modeling and statistical results. Our analysis provides an important step in better understanding the variability of natural background O 3 concentrations. The study has provided insight into stratospheric intrusions, with emphasis on the combined role of quasi-isentropic large-scale advection and mesoscale boundary layer turbulence for stratospheric air influencing enhanced surface O 3 .
A domain-filling, forward trajectory model originally developed for simulating stratospheric water vapor is used to simulate ozone (O 3 ) and carbon monoxide (CO) in the upper troposphere and lower stratosphere (UTLS). Trajectories are initialized in the upper troposphere, and the circulation is based on reanalysis wind fields. In addi-5 tion, chemical production and loss rates along trajectories are included using calculations from the Whole Atmosphere Community Climate Model (WACCM). The trajectory model results show good overall agreement with satellite observations from the Aura Microwave Limb Sounder (MLS) and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) in terms of spatial structure and seasonal variabil-10 ity. The trajectory model results also agree well with the Eulerian WACCM simulations. Analysis of the simulated tracers shows that seasonal variations in tropical upwelling exerts strong influence on O 3 and CO in the tropical lower stratosphere, and the coupled seasonal cycles provide a useful test of the transport simulations. Interannual variations in the tracers are also closely coupled to changes in upwelling, and the 15 trajectory model can accurately capture and explain observed changes during 2005-2011. This demonstrates the importance of variability in tropical upwelling in forcing chemical changes in the tropical UTLS. 25 1998; Wang and Dessler, 2012) all support this understanding. Back trajectory models 5992 ACPD 14, 5991-6025, 2014
Three-dimensional climatological distribution of tropospheric OH: Update and evaluation
Journal of Geophysical Research, 2000
A global climatological distribution of tropospheric OH is computed using distributions of O 3 , H 2 O, NO x , CO, hydrocarbons and cloud optical depth, specified from observations. Concentrations of OH are computed by forcing the system of kinetic equations to the periodic solution, with a period of 24 hours. The global annual mean concentration of OH is 1.16×10 6 mol cm −3 (integrated with respect to mass of air). Mean hemispheric concentrations of OH are within 1%. While the global mean OH increased by 33% compared to that from Spivakovsky et al. [1990], mean loss frequencies of CH 3 CCl 3 and CH 4 increased by only 23% because a lower fraction of the total OH resides in the lower troposphere in the present distribution. The value 277K used for determining lifetimes of HCFCs by scaling rate constants , is revised to 272K. The present distribution of OH is consistent within a few percent with the present budgets of CH 3 CCl 3 and HCFC-22. For CH 3 CCl 3 , it results in a lifetime of CH 3 CCl 3 of 4.7 years, including stratospheric and ocean sinks with atmospheric lifetimes of 43 and 78 years, respectively. For HCFC-22, the computed lifetime is 11.4, allowing for the stratospheric sink of 229 years. Industrial sources of CH 2 Cl 2 are sufficient for balancing its budget. Observed levels of CH 2 Cl 2 (annual means) suggest that no correction of hemispheric abundances of OH is necessary if the rate of interhemispheric mixing in the model is increased to the upper limit consistent with observations of CFCs and 85 Kr. If this rate is at its lower limit, an increase of OH in the northern hemisphere by 35% combined with a decrease in OH in the southern tropics by 60% is suggested by observations of CH 2 Cl 2 . However, such large corrections are inconsistent with observations for 14 CO in the tropics and for the interhemispheric gradient of CH 3 CCl 3 . The confluence of all available tests does not suggest significant discrepancies except for a possible underestimation of OH in the tropics in winter by 15-20%, and an overestimation in southern extratropics by ∼ 25%.