Very short-lived brominated substances (VSLBr) are an important source of stratospheric bromine, an effective ozone destruction catalyst. However, the accurate estimation of the organic and inorganic ...partitioning of bromine and the input to the stratosphere remains uncertain. Here, we report near-tropopause measurements of organic brominated substances found over the tropical Pacific during the NASA Airborne Tropical Tropopause Experiment campaigns. We combine aircraft observations and a chemistry–climate model to quantify the total bromine loading injected to the stratosphere. Surprisingly, despite differences in vertical transport between the Eastern and Western Pacific, VSLBr (organic + inorganic) contribute approximately similar amounts of bromine ∼6 (4–9) parts per thousand to the stratospheric input at the tropical tropopause. These levels of bromine cause substantial ozone depletion in the lower stratosphere, and any increases in future abundances (e.g., as a result of aquaculture) will lead to larger depletions.
We report observations of stratospheric CO 2 that reveal surprisingly large anomalous enrichments in 17 O that vary systematically with latitude, altitude, and season. The triple isotope slopes ...reached 1.95 ± 0.05(1σ) in the middle stratosphere and 2.22 ± 0.07 in the Arctic vortex versus 1.71 ± 0.03 from previous observations and a remarkable factor of 4 larger than the mass-dependent value of 0.52. Kinetics modeling of laboratory measurements of photochemical ozone–CO 2 isotope exchange demonstrates that non–mass-dependent isotope effects in ozone formation alone quantitatively account for the 17 O anomaly in CO 2 in the laboratory, resolving long-standing discrepancies between models and laboratory measurements. Model sensitivities to hypothetical mass-dependent isotope effects in reactions involving O 3 , O( 1 D), or CO 2 and to an empirically derived temperature dependence of the anomalous kinetic isotope effects in ozone formation then provide a conceptual framework for understanding the differences in the isotopic composition and the triple isotope slopes between the laboratory and the stratosphere and between different regions of the stratosphere. This understanding in turn provides a firmer foundation for the diverse biogeochemical and paleoclimate applications of 17 O anomalies in tropospheric CO 2 , O 2 , mineral sulfates, and fossil bones and teeth, which all derive from stratospheric CO 2 .
When will the Antarctic ozone hole recover? Newman, Paul A.; Nash, Eric R.; Kawa, S. Randolph ...
Geophysical research letters,
June 2006, Letnik:
33, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The Antarctic ozone hole demonstrates large‐scale, man‐made affects on our atmosphere. Surface observations now show that human produced ozone‐depleting substances (ODSs) are declining. The ozone ...hole should soon start to diminish because of this decline. We demonstrate a parametric model of ozone hole area that is based upon a new algorithm for estimating chlorine and bromine levels over Antarctica and late spring Antarctic stratospheric temperatures. This model explains 95% of the ozone hole area's variance. We then use future ODS levels to predict ozone hole recovery. Full recovery to 1980 levels will occur around 2068 and the area will very slowly decline between 2001 and 2017. Detection of a statistically significant decrease of area will not occur until about 2024. We further show that nominal Antarctic stratospheric greenhouse gas forced temperature change should have a small impact on the ozone hole.
We use the GEOS-Chem global 3-D atmospheric chemistry transport model to interpret atmospheric observations of bromoform (CHBr3) and dibromomethane (CH2Br2) collected during the CAST and CONTRAST ...aircraft measurement campaigns over the western Pacific, January–February 2014. We use a new linearized, tagged version of CHBr3 andCH2Br2, allowing us to study the influence of emissions from specific geographical regions on observed atmospheric variations. The model describes 32 %–37 % of CHBr3 and 15 %–45 % ofCH2Br2 observed variability during CAST and CONTRAST, reflecting model errors in vertical transport. The model has a mean positive bias of 30 % that is larger near the surface, reflecting errors in the poorly constrained prior emission estimates. We find using the model that observed variability of CHBr3 and CH2Br2 is driven by open ocean emissions where there is deep convection. Atmospheric variability above6 km includes a significant contribution from coastal oceans, but it is still dominated by emissions from the open ocean and by older air masses that originate upwind. In the absence of reliable ocean emission estimates, we use a new physical age-of-air simulation to determine the relative abundance of halogens delivered by CHBr3 and CH2Br2 to the tropical transition layer (TTL). We find that 76 % (92 %) of air masses that originate from the ocean reach the TTL within two (three) atmospherice-folding lifetimes of CHBr3 and almost all of them reach the TTL within one e-folding lifetime of CH2Br2. Over the duration of CAST and CONTRAST, and over our study region, oceans delivered a mean (range)CHBr3 and CH2Br2 mole fraction of 0.46 (0.13–0.72) and 0.88 (0.71–1.01) pptv, respectively, to the TTL, and a mean (range) Bry mole fraction of 3.14 (1.81–4.18) pptv from source gases to the upper troposphere.
Fluxes of halogenated volatile organic compounds (VOCs) over the Southern Ocean remain poorly understood, and few atmospheric measurements exist to constrain modeled emissions of these compounds. We ...present observations of CHBr3, CH2Br2, CH3I, CHClBr2, CHBrCl2, and CH3Br during the O2∕N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study and the second Atmospheric Tomography mission (ATom-2) in January and February of 2016 and 2017. Good model–measurement correlations were obtained between these observations and simulations from the Community Earth System Model (CESM) atmospheric component with chemistry (CAM-Chem) for CHBr3, CH2Br2, CH3I, and CHClBr2 but all showed significant differences in model : measurement ratios. The model : measurement comparison for CH3Br was satisfactory and for CHBrCl2 the low levels present precluded us from making a complete assessment. Thereafter, we demonstrate two novel approaches to estimate halogenated VOC fluxes; the first approach takes advantage of the robust relationships that were found between airborne observations of O2 and CHBr3, CH2Br2, and CHClBr2. We use these linear regressions with O2 and modeled O2 distributions to infer a biological flux of halogenated VOCs. The second approach uses the Stochastic Time-Inverted Lagrangian Transport (STILT) particle dispersion model to explore the relationships between observed mixing ratios and the product of the upstream surface influence of sea ice, chl a, absorption due to detritus, and downward shortwave radiation at the surface, which in turn relate to various regional hypothesized sources of halogenated VOCs such as marine phytoplankton, phytoplankton in sea-ice brines, and decomposing organic matter in surface seawater. These relationships can help evaluate the likelihood of particular halogenated VOC sources and in the case of statistically significant correlations, such as was found for CH3I, may be used to derive an estimated flux field. Our results are consistent with a biogenic regional source of CHBr3 and both nonbiological and biological sources of CH3I over these regions.
We infer surface fluxes of bromoform (CHBr3) and
dibromoform (CH2Br2) from aircraft observations over the western
Pacific using a tagged version of the GEOS-Chem global 3-D atmospheric
chemistry ...model and a maximum a posteriori inverse model. Using GEOS-Chem (GC) as
an intermediary, we find that the distribution of a priori ocean
emissions of these gases are reasonably consistent with observed atmospheric
mole fractions of CHBr3 (r=0.62) and CH2Br2
(r=0.38). These a priori emissions result in a positive model bias
in CHBr3 peaking in the marine boundary layer, but reproduce
observed values of CH2Br2 with no significant bias by virtue of
its longer atmospheric lifetime. Using GEOS-Chem, we find that observed
variations in atmospheric CHBr3 are determined equally by sources
over the western Pacific and those outside the study region, but observed
variations in CH2Br2 are determined mainly by sources outside
the western Pacific. Numerical closed-loop experiments show that the spatial
and temporal distribution of boundary layer aircraft data have the potential
to substantially improve current knowledge of these fluxes, with improvements
related to data density. Using the aircraft data, we estimate aggregated
regional fluxes of 3.6±0.3×108 and 0.7±0.1×108 g month−1 for CHBr3 and CH2Br2 over
130–155∘E and 0–12∘ N, respectively, which represent
reductions of 20 %–40 % of the prior inventories by Ordóñez
et al. (2012) and substantial spatial deviations from different a
priori inventories. We find no evidence to support a robust linear
relationship between CHBr3 and CH2Br2 oceanic
emissions, as used by previous studies. We find that over regions with dense
observation coverage, our choice of a priori inventory does not
significantly impact our reported a posteriori flux estimates.
The distribution of isotopes within O2 molecules can be rapidly altered when they react with atomic oxygen. This mechanism is globally important: while other contributions to the global budget of O2 ...impart isotopic signatures, the O(3P) + O2 reaction resets all such signatures in the atmosphere on subdecadal timescales. Consequently, the isotopic distribution within O2 is determined by O3 photochemistry and the circulation patterns that control where that photochemistry occurs. The variability of isotopic ordering in O2 has not been established, however. We present new measurements of 18O18O in air (reported as delta36 values) from the surface to 33 km altitude. They confirm the basic features of the clumped-isotope budget of O2: Stratospheric air has higher delta36 values than tropospheric air (i.e., more 18O18O), reflecting colder temperatures and fast photochemical cycling of O3. Lower delta36 values in the troposphere arise from photochemistry at warmer temperatures balanced by the influx of high-delta36 air from the stratosphere. These observations agree with predictions derived from the GEOS-Chem chemical transport model, which provides additional insight. We find a link between tropical circulation patterns and regions where delta36 values are reset in the troposphere. The dynamics of these regions influences lapse rates, vertical and horizontal patterns of O2 reordering, and thus the isotopic distribution toward which O2 is driven in the troposphere. Temporal variations in delta36 values at the surface should therefore reflect changes in tropospheric temperatures, photochemistry, and circulation. Our results suggest that the tropospheric O3 burden has remained within a +/-10 percent range since 1978.
A chemical ionization mass spectrometer was used to measure BrO and HOBr+Br2 over the Tropical West Pacific Ocean within the altitude range of 1 to 15km, during the CONvective TRansport of Active ...Species in the Tropics (CONTRAST) campaign in 2014. Isolated episodes of elevated BrO (up to 6.6pptv) and/or HOBr+Br2 (up to 7.3pptv) were observed in the tropical free troposphere (TFT) and were associated with biomass burning. However, most of the time we did not observe significant BrO or HOBr+Br2 in the TFT and the tropical tropopause layer (TTL) above our limits of detection (LOD). The 1min average LOD for BrO ranged from 0.6 to 1.6pptv and for HOBr+Br2 ranged from 1.3 to 3.5pptv. During one flight, BrO observations from the TTL to the extratropical lowermost stratosphere were used to infer a profile of inorganic bromine (Bry). Based on this profile, we estimated the product gas injection of bromine species into the stratosphere to be 2pptv. Analysis of Bry partitioning further indicates that BrO levels are likely very low in the TFT environment and that future studies should target the measurement of HBr or atomic Br. Key Points BrO observations throughout the tropics from 1 to 15km were typically below a limit of detection of 1pptv and were compatible with zero BrO and HOBr were observed at significant levels in biomass burning plumes in the tropical free troposphere Model calculations indicate that BrO is a minor constituent of Bry in the tropics and highlight the importance of measuring HBr in the future
Particle size distributions and gas‐phase particle precursors and tracer species were measured aboard an aircraft in the plumes downwind from industrial and urban sources in the vicinity of Houston, ...TX during the daytime in late August and early September 2000. Plumes originating from the Parish gas‐fired and coal‐fired power plant, petrochemical industries along the Houston ship channel, the petrochemical facilities near the Gulf coast, and the urban center of Houston were studied. Most of the particle mass flux advected downwind of Houston came from the industries and electrical utilities at the periphery of the city rather than from sources in the urban core. In SO2‐rich plumes that did not contain elevated concentrations of volatile organic compounds (VOCs), particle volume increased with increasing plume oxidation (age) at a rate consistent with condensation and neutralization of the gas‐phase oxidation products of SO2. In plumes that were rich in both SO2 and VOCs, observed particle growth greatly exceeded that expected from SO2 oxidation, indicating the formation of organic particulate mass. In plumes that were enhanced in VOCs but not in SO2, and in the plume of the Houston urban center, no particle volume growth with increasing plume oxidation was detected. Since substantial particle volume growth was associated only with SO2‐rich plumes, these results suggest that photochemical oxidation of SO2 is the key process regulating particle mass growth in all the studied plumes in this region. However, uptake of organic matter probably contributes substantially to particle mass in petrochemical plumes rich in both SO2 and VOCs. Quantitative studies of particle formation and growth in photochemical systems containing nitrogen oxides (NOx = NO + NO2), VOCs, and SO2 are recommended to extend those previously made in NOx–VOC systems.
Current stratospheric models have difficulties in fully explaining the observed midlatitude ozone depletion in the lowermost stratosphere, particularly near the tropopause. Such models assume that ...only long‐lived source gases provide significant contributions to the stratospheric halogen budget, while all the short‐lived compounds are removed in the troposphere, the products being rained out. Here we show this assumption to be flawed. Using bromine species as an example, we show that in the lowermost stratosphere, where the observed midlatitude ozone trend maximizes, bromoform (CHBr3) alone likely contributes more inorganic bromine than all the conventional long‐lived sources (halons and methyl bromide) combined.
PDF
