CH 4 AND N 2 O photochemical lifetimes in the upper stratosphere: In situ estimates using SAMS data (original) (raw)
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Correlations of stratospheric abundances of CH 4 and N 2 O derived from ATMOS measurements
Geophysical Research Letters, 1998
ATMOS measurements made over a wide range of altitudes and latitudes demonstrate compact correlations between mixing ratios of CH 4 and N20. Tight but distinct correlations are observed for the tropics, the springtime Arctic vortex, and the extra-tropics/extra-vortex regions, indicating dynamical isolation between these regions. Little variability is apparent in correlations between [CH4] and [N20] from measurements made in different years (1992, 1993, and 1994), seasons (March/April and November), and hemispheres. Introduction Lifetimes of long-lived trace species in the stratosphere vary substantially with photochemical environment, and the response to a change in environment is highly speciesdependent. The lifetime of CH4, for example, is controlled by the rate of oxidation via reactions with OH, O(•D), and C1, whereas the lifetime of N20 is determined by the rate at which it photolyzes or reacts with O(•D). Neither of these species has significant known sources in the stratosphere. Thus, their relative "instantaneous" lifetimes will vary with abundances of OH, C1, O(•D), and UV radiation, resulting in local relative concentrations that depend on the photochemical history of the air mass. In regions of the atmosphere where mixing occurs on time scales much shorter than these photochemical lifetimes, CH 4 and N20 distributions should be homogeneous, and correlations between them should collapse to a single value. Where horizontal mixing is rapid, correlations of these species should be compact, varying only with altitude [Plumb
Journal of Geophysical Research, 2000
Nitrous oxide (N20) and methane (CH4) were measured in the upper troposphere and lower stratosphere by multiple instruments aboard the NASA ER-2 aircraft during the 1995-1996 Stratospheric Tracers of Atmospheric Transport (STRAT) and 1997 Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) campaigns. Differences between coincidental, in situ measurements are examined to evaluate the agreement and variability in the agreement between these instruments during each flight. Mean N20 measurement differences for each flight were much smaller than limits calculated from quoted values of N20 measurement accuracy and for all but two flights were <8.7 ppb (3.5%). Mean CH 4 measurement differences for flights were similarly much smaller than calculated limits and for all but three flights were <65 ppb (4.4%). Typical agreement between instruments during flights averaged 6.2 ppb (2.5%) for N20 and 43 ppb (2.9%) for CH 4. In contrast, for about half of the flights, the variability of N20 and CH 4 measurement differences exceeded limits calculated from quoted values of measurement precision. The typical measurement difference variability (1 •) during a flight averaged _+8.0 ppb (3.2%) for N20 and _+43 ppb (2.9%) for CH 4. For some flights, large differences or variations in differences are attributable to the poor measurement accuracy or precision of one instrument. It is demonstrated that small offsets between the computer clocks of these instruments can result in significant differences between their "coincidental" N20 and CH 4 data, especially when there is high spatial variability in tracer abundance along a flight track.
Summertime photochemistry of the troposphere at high northern latitudes
Journal of Geophysical Research, 1992
The budgets of 03, NOx CNO+NO2), reactive nitrogen CNOy), and acetic acid in the 0-6 km column over western Alaska in summer are examined by photochemical modeling of aircraft and ground-based measurements from the Arctic Boundary Layer Expedition (ABLE 3A). It is found that concentrations of O3 in the region are regulated mainly by input from the stratosphere, and losses of comparable magnitude from photochemistry and deposition. The concentrations of NOx (10-50 ppt) are sufficiently high to slow down 03 photochemical loss appreciably relative to a NOx-free atmosphere; if no NOx were present, the lifetime of 03 in the 0-6 km column would decrease from 46 to 26 days because of faster photochemical loss. The small amounts of NOx present in the Arctic troposphere have thus a major impact on the regional 03 budget. Decomposition of peroxyacetyl nitrate (PAN) can account for most of the NOx below 4-km altitude, but for only 20% at 6-km altitude. Decomposition of other organic nitrates might supply the missing source of NOx. The lifetime of NOy in the ABLE 3A flight region is estimated at 29 days, implying that organic nitrate precursors of NOx could be supplied from distant sources including fossil fuel combustion at northem mid4atitudes. Biomass fire plumes sampled during ABLE 3A were only marginally enriched in 03; this observation is attributed in part to low NOx emissions in the fires, and in part to rapid conversion of NO• to PAN promoted by low atmospheric temperatures. It appears that fires make little contribution to the regional 03 budget. Only 30% of the acetic acid concentrations measured during ABLE 3A can be accounted for by reactions of CH3CO3 with HO2 and CH302. There remains a major unidentified source of acetic acid in the atmosphere. 1. INTRODUCTION ginally enriched in 03; and (3) high-O3 episodes were usually associated with stratospheric intrusions (documented by lidar). The The Arctic Boundary Layer Expedition (ABLE 3A) surveyed NO,• concentrations measured in ABLE 3A were in the range the composition of the North American Arctic and sub-Arctic troposphere from the surface to 6 km altitude during July-August 10-50 ppt [Sandholm et al., this issue], sufficiently low that photo-1988 [Harriss et al., this issue (a)]. Aircraft measurements in-chemistry should provide a net sink for 03. As discussed below, cluded concentrations of 03, NO, NO2, peroxyacetyl nitrate our analysis of the ABLE 3A data indicates thatO3 concentrations in the summertime Arctic troposphere represent largely a balance (PAN), HNO3, total reactive nitrogen (NO•), CO, non-methane between input from the stratosphere, and losses of comparable hydrocarbons (NMHCs), and organic acids. We examine in this paper the photochemical activity of the regional atmosphere docu-magnitude from photochemistry and deposition. A major point of the present paper is to show that anthropogenmented by the ABLE 3A data, with focus on the budgets of 03, NO• (NO+NO2), and NO•. ic influence on O3 levels in the Arctic may manifest itself not by Our principal objective is to explain the-1% yr-x rise of 03 long-range transport of pollution-derived 03, but rather by a decrease of the regional photochemical sink due to the presence of concentrations observed in the Arctic troposphere over the past two decades [Logan, 1985; Oltmans and Kornhyr, 1986]. This rise is most pronounced in summer, averaging 3% yr-x at Barrow in July for the period 1973-1984 [Oltrnans and Kornhyr, 1986]. Anthropogenic influence would provide a logical explanation. However, the ABLE 3A data clearly point to a stratospheric rather than to a pollution origin for O3 in the region [Browell et al., this issue; Gregory et al., this issue]. This source attribution is based on three pieces of evidence: (1) concentrations of O3 in the middle troposphere were anticorrelated with concentrations of aerosol, H20, and CO; (2) well-defined layers of pollution were only mar
Journal of Geophysical Research, 1992
Partitioning of the major components of the reactive nitrogen and inorganic chlorine reservoirs is derived from aircraft measurements in the lower stratosphere during the winter season in both hemispheres at latitudes of about 60 ø to 80 ø . The goal of this work is to exercise the power of the correlated set of measurements from polar missions of the NASA ER-2 to extend what can be leamed from looking at the measurements individually. The results provide a consistent method for comparing distributions, and hence the controlling processes, between different areas of the near-polar regions. The analysis provides clear evidence of the effects of heterogeneous processes in the atmosphere. Values for NO 2, C1ONO2, N205, and C1202 are derived in a simplified steady state model based on in situ NO, C10, O 3, temperature, and pressure measurements; laboratory-measured reaction rates; and modeled photodissociation rates. Values for the reservoir totals are independently derived from measurements of N 20, organic chlorine, and total reactive nitrogen. The relative abundances of the measured and derived species within the reservoirs are calculated, and the longer-lived species HC1 and HNO 3 are estimated as the residuals of their respective reservoirs. The resulting latitude distributions in the Arctic outside the vortex agree reasonably well with predictions of a two-dimensional photochemical model, indicating that partitioning in this region is largely controlled by standard homogeneous gas phase chemistry. Inside the Arctic vortex a large fraction of the HC1 has been converted to reactive chlorine species C10 and C1202, consistent with the extensive action of known heterogeneous reactions, presumably occurring on the surfaces of polar stratospheric clouds formed in the cold temperatures of the vortex. The partitioning in the Antarctic suggests that nearly the entire range of latitudes sampled by the ER-2 is affected by heterogeneous processes in situ, including that portion of the "collar" region equatorward of the nominal chemically perturbed region (CPR).
Atmospheric Chemistry and Physics, 2013
Long lived halogen-containing compounds are important atmospheric constituents since they can act both as a source of chlorine radicals, which go on to catalyse ozone loss, and as powerful greenhouse gases. The long term impact of these species on the ozone layer is dependent on their stratospheric lifetimes. Using observations from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) we present calculations of the stratospheric lifetimes of CFC-12, CCl 4 , CH 4 , CH 3 Cl and N 2 O. The lifetimes were calculated using the slope of the tracer-tracer correlation of these species with CFC-11 at the tropopause. The correlation slopes were corrected for the changing atmospheric concentrations of each species based on age of air and CFC-11 measurements from samples taken aboard the Geophysica aircraftalong with the effective linear trend of the VMR from tropical ground-based AGAGE sites. Stratospheric lifetimes were calculated using a CFC-11 lifetime of 45 yr. These calculations produced values of 113 + (−)26(18) yr (CFC-12), 35 + (−)11(7) yr (CCl 4), 195 + (−)75(42) yr (CH 4), 69 + (−)65(23) yr (CH 3 Cl) and 123 + (−)53(28) yr (N 2 O). The errors on these values are the weighted 1-σ non-systematic errors. The stratospheric lifetime of CH 3 Cl represents the first calculations of the stratospheric lifetime of CH 3 Cl using data from a space based instrument. ACPD 13, 4221-4287, 2013 Stratospheric lifetimes of CFC-12, CCl 4 , CH 4 , CH 3 Cl and N 2 O A. T. Brown et al.
Journal of Geophysical Research, 1999
A model of atmospheric photochemistry and transport has been developed and applied toward investigating global tropospheric chemistry. The Model of Atmospheric Transport and Chemistry - Max-Planck-Institute for Chemistry version (MATCH-MPIC) is described and key characteristics of its global simulation are presented and compared to available observations. MATCH-MPIC is an "offline" model which reads in gridded time-dependent values for the most basic meteorological parameters (e.g., temperature, surface pressure, horizontal winds), then uses these to compute further meteorological parameters required for atmospheric chemistry simulations (convective transport, cloud microphysics, etc.). The meteorology component of MATCH-MPIC simulates transport by advection, convection, and dry turbulent mixing, as well as the full tropospheric hydrological cycle (water vapor transport, condensation, evaporation, and precipitation). The photochemistry component of MATCH-MPIC represents the major known sources (e.g., industry, biomass burning), transformations (chemical reactions and photolysis), and sinks (e.g., wet and dry deposition) which affect the O3hyphen;HOx-NOy-CH4-CO photochemical framework of the "background" troposphere. The results of two versions of the model are considered, focusing on the more recent version. O3 is in relatively good agreement with observed soundings, although it is generally underestimated at low levels and overestimated at high levels, particularly for the more recent version of the model. We conclude that the simulated stratosphere-troposphere flux of O3 is too large, despite the fact that the total flux is 1100 Tg(O3)/yr, whereas the upper limit estimated in recent literature is over 1400 Tg(O3)/yr. The OH distribution yields a tropospheric CH4 lifetime of 10.1 years, in contrast to the lifetime of 7.8 years in the earlier model version, which nearly spans the range of current estimates in the literature (7.5-10.2 years). Surface CO mixing ratios are in good agreement with observations. NO is generally underestimated, a problem similar to what has also been found in several other recent model studies. HNO3 is also considerably underestimated. H2O2 and CH3OOH, on the other hand, are in relatively good agreement with available observations, though both tend to be underestimated at high concentrations and overestimated at low concentrations. Possible reasons for these differences are considered.
Abstract. Long lived halogen-containing compounds are important atmospheric constituents since they can act both as a source of chlorine radicals, which go on to catalyse ozone loss, and as powerful greenhouse gases. The long-term impact of these species on the ozone layer is dependent on their stratospheric lifetimes. Using observations from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) we present calculations of the stratospheric lifetimes of CFC-12, CCl4, CH4, CH3Cl and N2O. The lifetimes were calculated using the slope of the tracer–tracer correlation of these species with CFC-11 at the tropopause. The correlation slopes were corrected for the changing atmospheric concentrations of each species based on age of air and CFC-11 measurements from samples taken aboard the Geophysica aircraft – along with the effective linear trend of the volume mixing ratio (VMR) from tropical ground based AGAGE (Advanced Global Atmospheric Gases Experiment) sites. Stratospheric lifetimes were calculated using a CFC- 11 lifetime of 45 yr. These calculations produced values of 113 + (−) 26 (18) yr (CFC-12), 35 + (−) 11 (7) yr (CCl4), 69 + (−) 65 (23) yr (CH3Cl), 123 + (−) 53 (28) yr (N2O) and 195 + (−) 75 (42) yr (CH4). The errors on these values are the weighted 1 non-systematic errors. Systematic errors were estimated by recalculating lifetimes using VMRs which had been modified to reflect differences between ACE-FTS retrieved VMRs and those from other instruments. The results of these calculations, including systematic errors, were as follows: 113 + (−) 32 (20) for CFC-12, 123 + (−) 83 (35) for N2O, 195 + (−) 139 (57) for CH4, 35 + (−) 14 (8) for CCl4 and 69 + (−) 2119 (34) yr for CH3Cl. For CH3Cl & CH4 this represents the first calculation of the stratospheric lifetime using data from a space based instrument.
Journal of Geophysical Research, 1998
Correlations are presented for [NOy] relative to [N20] and [03] derived from measurements from the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument from a wide rmlge of altitudes mid latitudes, including the tropics for which previous analyses have not extended above ~20 km. Relationships for [03] versus [N20] are also given. The results are shown to be in good agreement with aircraft-mid balloon-based observations. Distinct con'elations are obse•wed for the tropics, the springtime polar vortex, and the extratropics-extravortex regions. These con'elations demonstrate rapid production of NOy and 03 in the tropical middle stratosphere and episodic export of air from this region to higher latitudes. Isolation of air within the developing polar vortices in the fall is also shown. Arctic vortex data from April 1993 appear to indicate denitrification of 25-30%, which is evident as a 3.0-4.5 ppb deficit in [NOy] when the vortex [NOy]: [N20] con'elation is compared with the extravortex con'elation. A mixtm-e of air descended fi'om above 40 km with air from lower altitudes can fully account tbr this deficit in [NOy], in addition to approximately half of rul apparent Arctic ozone loss of 50-60%, as infen'ed by compm'ison of the vortex and extravortex [O3]:[N:O] correlations. Comparison of Antarctic vortex and extravortex con'elations from November 1994 similm'ly show a 60-80% deficit in [NOy] and 80-100% deficit in [OLd]: at least half of this apparent denitrification and ozone loss can be attributed to mixing of air descended from higher altitudes with air fi'om lower altitudes. ] ([Z] = mixing ratio of species Z). Although the relationship between [NOy] and [03] has also been used to identify chemically perturbed vortex air [ProJ[}'tt et at., 1989; Kondo et at., 1992, 1994; Weinheimer et al., 1993], this correlation has recently been used in investiga-the combined set of [NOy]'[N20] and [O3]'[N20] correlations has been used to estilnate mass flux of stratospheric air into the troposphere [Murphy and Fahey, 1994]. Although highly accurate and precise in situ tracer observations are uniquely suited for such detailed studies, these measurements are spatially restricted either to the lower stratosphere (below •20 kin) by the current altitude limitations of stratospheric aircraft or to midlatitudes and high latitudes because of complications associated with deploying stratospheric balloons in the tropics. Observations made by the Atmospheric Trace Molecule Spectroscopy instrument (ATMOS), although not as well suited to detailed studies of transport in the lower stratosphere and upper troposphere, allow the altitude/latitude coverage for N Oy species to extend well beyond the range currently attainable with in situ methods, particularly in the tropics. We report here tracer correlations derived from measurements from the Atmospheric Laboratory for Applications and Science (ATLAS) missions, for which ATMOS Version 2 data are available [Abrams et al., 1996a; Gunson et al., 1996]. Mixing ratios of 03 are presented relative to those of N20. Total reactive nitrogen, [NO,,], as derived from the sum of the major constituents, is shown relative to [N20 ] and [03]. The corre-28,347 28,348 MICHELSEN ET AL.' CORRELATIONS OF STRATOSPHERIC NOy, 03, N20, AND CH4 lations are demonstrated to be internally consistent and in agreement with previous observations. Polynomial fits to the correlations are given in addition to expressions for deriving [N20 ] froin xneasured [CH4]. These fits are useful for comparison with other measurements and multidimensional model predictions. In addition, they can be used to infer [NOy] from measured [N20 ], [O3], or [CH4] throughout the stratosphere and to aid in the identification of air masses recently transported between regions within the stratosphere. Furthermore, trends in the relative abundances of these species are small (<1%/yr [World Meteorological Organization, 1995]) and/or coupled (since NOy is predominantly produced by reaction of O(•D) with N:O, a small increase in [03] will lead to a proportional increase in [NOy] and decrease in [N20]), yielding little 1V[ICHELSEN ET AL.: CORRELATIONS OF STRATOSPHERIC NOy, 03, N20, AND CH4 28,349 a 05, ß © AT-3: 3-10øN © AT-3: 28-46øN o AT-2: 63-69øN ß AT-3:Proto-vortex [:3 AT-2:Arctic vortex ""'0 1" b .. + AT-1' •' x AT-1' Piesch, Spatial m•d temporal variability of C1ONO2, HNO3, and 03 in the Arctic winter of 1992/1993 as obtained by airborne infrared emission spectroscopy, J. Geophys. Res., 100, 9101-9114, 1995. Brasseur, G., and S. Solomon, Aeronomy of the Middle Atmosphere, 2nd ed., D. Reidel, Norwell, Mass., 1986. Bregman, A., et al., Aircraft measurements of 03, HNO3, and N20 in the winter Arctic lower stratosphere during the Stratosphere-Troposphere Experiment by Aircraft Measurements (STREAM) 1, J. Geophys. Res., 100, 11,245-11,260, 1995. Bregman, A.,, M. van den Broek, K. S. Carslaw, R. Mtiller, T. Peter, M. P. Scheele, and J. Lelieveld, Ozone depletion in the late winter lower Arctic stratosphere: Observations and model results, J. Geophys. Res., 102, 10,815-10,828, 1997. Chang, A. Y., et al., A comparison of measurements from ATMOS and 28,358 MICHELSEN ET AL.: CORRELATIONS OF STRATOSPHERIC NOy, 03, N20, AND CH4 instruments aboard the ER-2 aircraft' Tracers of atmospheric transport, Geophys. Res. Lett., 23, 2389-2392, 1996. Crewell, S., D. Cheng, R. S. de 7•afra, and C. Trimble, Millimeter wave spectroscopic measurements over the South Pole, 1, A study of stratospheric dynamics using N20 observations, J. Geopttys. Res., A diagnostic for denitrification in the winter polar stratospheres, Nature, 345, 698-702, 1990. Fahey, D. W., et al., In situ observations of NOy, 03, and the NOy/O3 ratio in the lower stratosphere, Geophys. Res. Lett., 23, 1653-1656, 1996. Garcia, R. R., and S. Solomon, A new numerical model of the middle atmosphere, 2, Ozone and related species, J. Geophys. Res., 99, 12,937-12,951, 1994. Grant, W. B., E. V. Browell, C. S. Long, L. L. Stowe, R. G. Grainger, and A. Lambert, Use of volcanic aerosols to study the tropical stratospheric reservoir, Laminae in the tropical middle stratosphere: Origin and age estimation, Geophys. Res. Lett., in press, 1998. J Kawa, S. R., R. A. Plumb, and U. Schmidt, Simultaneous observations of long-lived species, in Ttte Atmospheric Effects of Stratospheric Aircraft: Report of the 1992 Models and Measurements Workshop, edited by M. J. Prather and E. E. Remsberg Chapter H, NASA Ref. Pub., 1292, 1993. Keim, E. R., et al., Measurements of the NOy-N20 correlation in the lower stratosphere: Latitudinal and seasonal changes and model comparisons, concentration of ozone in one-dimensional and two-dimensional models, J. Geophys. Res., 94, 9889-9896, 1989.
Evaluation of source gas lifetimes from stratospheric observations
Journal of Geophysical Research: Atmospheres, 1997
Simultaneous in situ measurements of the long-lived trace species N20, CH4, CFC-12, CFC-113, CFC-11, CC14, CH3CC13, H-1211, and SF6 were made in the lower stratosphere and upper troposphere on board the NASA ER-2 high-altitude aircraft during the 1994 campaign Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft. The observed extratropical tracer abundances exhibit compact mutual correlations that show little interhemispheric difference or seasonal variability except at higher altitudes in southern hemisphere spring. The environmental impact of the measured source gases depends, among other factors, on the rate at which they release ozone-depleting chemicals in the stratosphere, that is, on their stratospheric lifetimes. We calculate the mean age of the air from the SF 6 measurements and show how stratospheric lifetimes of the other species may be derived semiempirically from their observed gradients with respect to mean age at the extratropical tropopause. We also derive independent stratospheric lifetimes using the CFC-11 lifetime and the slopes of the tracer' s correlations with CFC-11. In both cases, we correct for the influence of tropospheric growth on stratospheric tracer gradients using the observed mean age of the air, time series of observed tropospheric abundances, and model-derived estimates of the width of the stratospheric age spectrum. Lifetime results from the two methods are consistent with each other. Our best estimates for stratospheric lifetimes are 122 + 24 years for N2 ¸, 93 + 18 years for CH4, 87 + 17 years for CFC-12, 100 + 32 years for CFC-113, 32 + 6 years for CC14, 34 + 7 years for CH3CC13, and 24 + 6 years for H-1211. Most of these estimates are significantly smaller than currently recommended lifetimes, which are based largely on photochemical model calculations. Because the derived stratospheric lifetimes are identical to atmospheric lifetimes for most of the species considered, the shorter lifetimes would imply a faster recovery of the ozone layer following the phaseout of industrial halocarbons than currently predicted. 1. Introduction Source gases of natural and/or anthropogenic origin may influence the environment in two ways. First, they affect the chemical composition of the atmosphere, most importantly stratospheric ozone levels by providing sources of halogen, hydrogen, and nitrogen in the stratosphere. When these source gases are decomposed in the stratosphere, usually by photolysis and reactions with O(1D) or OH, the degradation products Ibrm reactive species that participate in the catalytic destruction of ozone [Crutzen, 1970; Molina and Rowland, 1974]. Second, most source gases are also very efficient "greenhouse gases"; that
Journal of Geophysical Research, 1995
Aircraft sampling has provided extensive in situ and flask measurements of organic chlorine species in the lower stratosphere. The recent Airborne Arctic Stratospheric Expedition II (AASE II) included two independent measurements of organic chlorine species using whole air sample and real-time techniques. From the whole air sample measurements we derive directly the burden of total organic chlorine (CCly) in the lower stratosphere. From the more limited real-time measurements we estimate the CCly burden using mixing ratios and growth rates of the principal CCly species in the troposphere in conjunction with results from a two-dimensional photochemical model. Since stratospheric chlorine is tropospheric in origin and tropospheric mixing ratios are increasing, it is necessary to establish the average age of a stratospheric air parcel to assess its total chlorine (C1Total) abundance. Total inorganic chlorine (Cly) in the parcel is then estimated by the simple difference, Cly-C1Tota 1-CCly. The consistency of the results from these two quite different techniques suggests that we can determine the CCly and Cly in the lower stratosphere with confidence. Such estimates of organic and inorganic chlorine are crucial in evaluating the photochemistry controlling chlorine partitioning and hence ozone loss processes in the lower stratosphere.