摘要:

A Lagrangian chemical model is used to simulate the formation of the Antarctic “ozone hole”: the decrease in high‐latitude southern hemisphere ozone between mid‐August and mid‐September of each year. The model benchmark simulation of HNO3, ClONO2, ClO, and ozone for September 17, 1992, is in good agreement with UARS observations. Simulations of the ozone column over the years 1979–1994 show quantitative agreement with the secular decline in Antarctic ozone and change in the area of the ozone hole as observed by the total ozone mapping spectrometer (TOMS). The model calculates that the Antarctic ozone loss and ozone hole area both increased linearly with time after the early 1970s until the early 1990s. After the early 1990s the growth of the area of the ozone hole slows as a result of the slowing of the growth rate of total inorganic chlorine. A hypothetical doubling of the 1992 atmospheric chlorine amount would expand the ozone hole to the very edge of the p

ISSN:0148-0227    

DOI:10.1029/96JD01707

年代:1996

数据来源: WILEY

摘要:

Ground‐based observations of stratospheric ClO, N2O, and HNO3were made almost continuously at McMurdo Station, Antarctica (77.9°S, 166.6°E), during the austral spring of 1994, using two separate microwave receivers. Vertical profiles of these trace gases have been retrieved from the pressure broadened emission spectra between September 4 and October 8, 1994. In early September, McMurdo was located well inside the polar vortex, and high mixing ratios of chlorine monoxide (up to 1.8 ppbv) were measured in the lower stratosphere. Because of vortex movement, later measurements were taken in edge regions, where ClO was found to be quite variable. This vortex movement also provided an opportunity to study relative changes between all three species. Almost no HNO3was seen below 20 km during the measurement period, indicating that stratospheric air had been efficiently denitrified by polar stratospheric cloud formation. A significant increase of the nitric acid column was observed only around September 20, when McMurdo was closer to the outer edge of the vortex. At the beginning of the measurements, the vertical profiles of the inert tracer N2O had already descended so far that very little N2O was present above 20 km. During the observation period, the N2O distribution did not show strong changes except for a slight downward trend which increased with altitude. This indicates, as noted in previous years, that subsidence continued in the stratosphere over McMurdo Station until at least early October, when measurements were stopped. The temporal correlations between the behavior of ClO, N2O, HNO3, altitude, and temperature at the 50‐hPa level, and of ozone measured by local ozonesondes show that changes in the atmospheric composition were partly due to dynamic effects. A backward trajectory analysis was performed to interpret the ClO data in an attempt to clarify some irregular

ISSN:0148-0227    

DOI:10.1029/96JD01701

年代:1996

数据来源: WILEY

摘要:

Although only 15 years of continuous global satellite data are available, existing measurements are consistent with a significant, in‐phase solar cycle variation of upper stratospheric ozone and temperature. Here we investigate the latitude and seasonal dependences of this variation using 15 years (1979–1993) of combined solar backscattered ultraviolet (SBUV) and SBUV/2 ozone profile measurements and 14 years (1980–1995) of National Meteorological Center (NMC) temperature analyses. These dependences are estimated by applying a multiple regression statistical model to monthly zonal mean time series extending from 60°S to 60°N latitude and approximately 25‐ to 50‐km altitude. Solar variability is represented in the statistical model by the Mg II index, a close proxy for solar UV variations at wavelengths that affect the photochemical production of ozone. In agreement with earlier studies, although an apparent solar cycle variation of both ozone and temperature is present in the upper stratosphere, no detectable solar cycle variation is present in the middle stratosphere (30‐ to 35‐km altitude). Ozone increases of 4 – 6% from solar minimum to solar maximum are found near 2 mbar at middle latitudes, with comparable amplitudes in both summer and winter hemispheres. While the presence of a large positive ozone response in the northern hemisphere during winter appears to be qualitatively consistent with theoretical predictions, the amplitude of the observed ozone variation is nearly twice as large as estimates based on current two‐dimensional models of the middle atmosphere. Temperature increases of 2.5 K are found near 1 mbar at low latitudes throughout the year, in addition to a seasonally varying temperature response of 2.5 – 3 K near 5 mbar at middle and high latitudes in the summer hemisphere. A one‐dimensional radiative model is used to calculate the expected change in equilibrium temperature associated with the observed solar cycle variability in the ozone profile under the assumption of fixed dynamical heating (FDH). Near the equatorial stratopause, the temperature response calculated with the FDH model is within 0.5 K of the observed response. At higher latitudes near 4 mbar, the FDH model cannot account for the large amplitudes and strong latitude dependences of the NMC‐derived temperature variation. This would suggest that changes in stratospheric dynamics over the 11‐year solar cycle may also be important for understanding the observed tempe

ISSN:0148-0227    

DOI:10.1029/96JD01817

年代:1996

数据来源: WILEY

摘要:

Absorption spectra of NO2measured at several temperatures between room temperature and 197 K are used to improve the analysis of zenith view, atmospheric absorption data in the 405–430 nm spectral range. The size of persistent features in the residual spectrum of the analysis is reduced by up to 50%, which in principle facilitates measurement of weakly absorbing species, such as OClO and IO. Details of the reduction algorithm are discusse

ISSN:0148-0227    

DOI:10.1029/96JD01699

年代:1996

数据来源: WILEY

摘要:

The uncertainty in computed species concentrations resulting from measurement imprecision in reaction rate components is investigated in two tropospheric photochemical models. In this study, which extendsThompson and Stewart[1991], we perform statistical analysis on reaction rate coefficients to focus on two aspects of model uncertainty: (1) the change in the magnitude of concentration uncertainty as temperature varies throughout a model grid and (2) the difference resulting from selection of mean, as opposed to median, rates for model calculations. Reaction rates are treated as realizations of random variables having statistical properties given by component terms and their imprecisions. These assumptions lead to expressions for probability distributions of bimolecular rates and for the high‐ and low‐pressure limits for termolecular and thermolytic processes. They also imply that bimolecular rates and high‐ and low‐pressure limits used in photochemical models correspond to median values taken from a lognormal distribution. We derive analytic expressions for mean values, which are always larger than the medians, an intrinsic property of lognormal variables. We suggest that comparison of species concentrations computed using median and mean rates can provide some measure of the effect of rate imprecision in multidimensional models. We also find that the temperature dependence derived for the imprecision in bimolecular rates differs from that given in standard references, with our expression giving a smaller increase in imprecision as temperatures deviate from 298 K. Results are illustrated using a box and a one‐dimensional (1

ISSN:0148-0227    

DOI:10.1029/96JD01708

年代:1996

数据来源: WILEY

摘要:

The development of the wake vortex system behind an airplane (B‐747) at cruising altitude (8–15 km) and the dispersion of the aircraft emissions due to this vortex system have been studied by means of a two‐dimensional numerical model. Simulation experiments are presented which examine the influence of atmospheric stratification and vertical wind shear on the combined vortex‐emission system. Although the development of the vortex wake system can be influenced by three‐dimensional effects (e.g., Crow instabilities), the undisturbed process can be approximated as a two‐dimensional phenomenon, which allows the study of details of the vortex structures at small scales (lengthL≈ 1 m) and the dispersion of engine exhausts at larger scales (L≈ 100 m). The results of simulation experiments show that the maximum lifetime of the wake vortices (120 s ≤Tv≲ 300 s) as well as the descending rate (1.2 m s−1≤wv≤ 2.4 m s−1) and the dispersion of the emitted substances depend on the atmospheric stratification as well as vertical wind shear, but buoyancy forces seem to dominate over shear forces. The overall dispersion of aircraft emissions due to the wake vortex system can be quantified by a vertical standard deviation for the entir

ISSN:0148-0227    

DOI:10.1029/96JD02013

年代:1996

数据来源: WILEY

摘要:

A 5‐year simulation of supersonic aircraft exhaust using a three‐dimensional transport model has been completed using winds from the NASA/Goddard data assimilation system. A tracer based on emission rates of reactive nitrogen species (NOy) for all forecasted flight routes is continuously injected into the model. A parameterized upper stratospheric loss mechanism and a tropospheric sink due to rainout approximately balance the nitrogen emissions after several years of integration. Maximum values for exhaust NOyoccur during the northern hemisphere (NH) summer months, and minimum values occur during winter. The pollutant is most zonally asymmetric during the NH summer. The peak values are never more than twice the zonal mean. This supports the use of zonally averaged two‐dimensional models to evaluate the impact of the exhaust on the lower stratospheric composition. Budget calculations from the transport model show that most exhaust released in the NH is transported downward into the troposphere, where it is destroyed. In the model, about 15–20% of exhaust released poleward of 30°N is transported into the tropics, where it is lofted. The stratospheric residence time for the exhaust is estimated to be 1

ISSN:0148-0227    

DOI:10.1029/96JD01700

年代:1996

数据来源: WILEY

摘要:

In July and August of 1989 the National Center for Atmospheric Research (NCAR) Sabreliner jet aircraft was used to probe electrically active and inactive convective storms over west central New Mexico to examine the production of odd nitrogen in the middle and upper troposphere by thunderstorms. In the anvil outflow or cloud top region of active and nonactive storms, the majority of flights showed that O3was reduced relative to the extracloud air owing to transport of ozone‐poor air from lower altitudes. A similar result was found for active nitrogen (NOx) and total odd nitrogen (NOy) in nonelectrically active storms, but the reduction in NOywas also enhanced by removal of soluble constituents during convective transport. Examples of efficient removal from the gas phase are described. There was no evidence of O3production by lightning discharges. Indeed, O3was a good tracer over the lifetime (∼1 hour) of the storms. During the active‐to‐mature stage of air mass thunderstorms, large enhancements in active nitrogen were observed in the anvil altitude region (9–11.8 km) and, in one case, in the midlevel outflow (near 7 km) of a dissipating thunderstorm. Two thunderstorms allow good estimates of the NOxproduction by lightning within or transport to the upper altitude region (8–11.8 km). Thunderstorms of August 12 and August 19 yield amounts in the range of 253–296 kg(N) and 263–305 kg(N), respectively. If, as an exercise, these amounts are extrapolated to the global scale on the basis of the number of cloud‐to‐ground and intracloud lightning flashes counted or estimated for each storm and a global flash frequency of 100 s−1the result is 2.4–2.7 and 2.0–2.2 Tg(N)/yr. Alternatively, an estimate for the two storms made on the basis of the average number of thunderstorms that occur per day globally (44,000) yields amounts in the range of 4.1–4.7 and 4.2–4.9 Tg(N)/yr, respectively. These estimates only apply to the production or transport of lightning‐generated NOxin or to the altitude region between 8 km and the top of the thunderstorm anvil (∼11.8 km in these studies). Since in some large‐scale models, lightning‐generated NOxis equally distributed by mass into each tropospheric layer, our estimates are roughly equivalent to those model runs that use a global source strength of about twice our estimate for the upper altitude region. In several flights where the region below the base of thunderstorms was examined, no large enhancements in odd nitrogen which could be clearly attributed to lightning were observed. Apparently, the aircraft was not in the right place at the right time. Thus no estimate of the NOxproduction by lightning t

ISSN:0148-0227    

DOI:10.1029/96JD01706

年代:1996

数据来源: WILEY

摘要:

The reactions of organic peroxy radicals with NO, HO2, organic peroxy radicals, and NO3along with the formation and decomposition of peroxyacetyl nitrate are all important for the modeling of atmospheric chemistry. Recent laboratory measurements of the rate constants for peroxy radical‐peroxy radical reactions show that there are large differences between these rate constants. We present methods of estimating organic peroxy radical self‐reaction rate constants from an empirical expression. These self‐reaction rate constants may be used to estimate the rates of peroxy radical cross reactions. There are also new data available on the rate constants for peroxyacetyl nitrate formation, decomposition, the reaction of acetyl peroxy radicals and other organic peroxy radicals with NO, and the reactions of NO3with organic peroxy radicals. To estimate the importance of these reactions, these new data along with revisions to the product yields for organic peroxy radical‐organic peroxy radical reactions were implemented in the mechanism ofStockwell et al.[1990]. The revised mechanism yields significantly different concentrations of peroxyacetyl nitrate, higher organic hydroperoxides and peroxyacetic acid concentrations. Nighttime concentrations of organic peroxy radicals, HO2, HO, and NO3are also strongly affected by organic peroxy radical‐organic peroxy radical reactions and the reactions of organic peroxy radicals with NO3. Our results suggest that the reactions of organic peroxy radicals with NO3are more important than organic peroxy radical‐organic peroxy radical reactions in the nighttime

ISSN:0148-0227    

DOI:10.1029/96JD01519

年代:1996

数据来源: WILEY

摘要:

The reactive uptake coefficients (γ) of NO3onto pure water and dilute solutions of NaCl, NaBr, and NaNO2were measured using a wetted‐wall flow‐tube setup combined with a long‐path absorption cell for the detection of NO3. The measured γ values were in the range 1.5 × 10−4– 6 × 10−3, depending on the salt concentration in the water. By measuring γ as a function of salt concentration, HD��0.5for NO3in water was determined to be (1.9 ± 0.4) × 10−3Matm−1cm s−0.5at 273 K, assuming that the rate coefficient for the reaction of NO3with Cl−is 2.76 × 106M−1s−1at 273 K. The Henry's law coefficient for NO3in water is estimated to be 0.6 ± 0.3Matm−1, assuming that the diffusion coefficient of NO3in water isD��= (1.0 ± 0.5) × 10−5cm2s−1. Uptake of NO3on pure water is interpreted as due to reaction of NO3(aq)with H2O(��)to produce HNO3and OH in the liquid phase. Implications of these findings to the chemistry of

ISSN:0148-0227    

DOI:10.1029/96JD01844

年代:1996

数据来源: WILEY