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1.
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2.
This study examines the processes controlling the diurnal variability of ozone (O3) in the marine boundary layer of the Kwajalein Atoll, Republic of the Marshall Islands (latitude 8° 43′ N, longitude 167° 44′ E), during July to September 1999. At the study site, situated in the equatorial Pacific Ocean, O3 mixing ratios remained low, with an overall average of 9–10 parts per billion on a volume basis (ppbv) and a standard deviation of 2.5 ppbv. In the absence of convective storms, daily O3 mixing ratios decreased after sunrise and reached minimum during the afternoon in response to photochemical reactions. The peak-to-peak amplitude of O3 diurnal variation was approximately 1–3 ppbv. During the daytime, O3 photolysis, hydroperoxyl radicals, hydroxyl radicals, and bromine atoms contributed to the destruction of O3, which explained the observed minimum O3 levels observed in the afternoon. The entrainment of O3-richer air from the free troposphere to the local marine boundary layer provided a recovery mechanism of surface O3 mixing ratio with a transport rate of 0.04 to 0.2 ppbv per hour during nighttime. In the presence of convection, downward transport of O3-richer tropospheric air increased surface O3 mixing ratios by 3–12 ppbv. The magnitude of O3 increase due to moist convection was lower than that observed over the continent (as high as 20–30 ppbv). Differences were ascribed to the higher O3 levels in the continental troposphere and weaker convection over the ocean. Present results suggest that moist convection plays a role in surface-level O3 dynamics in the tropical marine boundary layer.  相似文献   

3.
Reactive halogen species (RHS = X, XO, HOX, OXO; X = Cl, Br, I) are known to have an important influence on the chemistry in the polar boundary layer (BL), where they are responsible for ozone depletion events in spring. Recent field campaigns at Mace Head, Ireland, and the Dead Sea, Israel, identified for the first time iodine oxide (IO) at mixing ratios of up to 6.6 ppt and 90 ppt bromine oxide (BrO), respectively, by DOAS also at lower latitudes. These results intensified the discussion about the role of the RHS in the mid-latitude BL.Photochemical box model calculations show that the observed IO mixing ratios can destroy ~0.45 ppb ozone per hour. This is comparable to the rates of the known O3-loss processes in the boundary layer. The model studies also reveal that IO, at these levels, has a strong influence on the BL photochemistry, increasing the OH/HO2- and the NO2/NO - ratios. In combination these changes lead to a reduction of the photochemical ozone formation, which - in addition - reduces ozone mixing ratios by up to 0.15 ppb/h.The studies for the Dead Sea case give no information on the heterogeneous process responsible for the bromine release, but they show that a total of 2 – 4 ppb of total bromine have to be released to explain the observed complete depletion of 60 ppb ozone in 2 – 3 hours.  相似文献   

4.
Chemical amplification, CA, a method commonly used for the detection of peroxy radicals, HO2 and RO2, was found to be sensitive towards ClOx (Cl+ClO+OClO) as well. ClOx is reduced by NO to Cl atoms which react with carbon monoxide in the presence of O2. The reaction sequence thus initiated oxidizes CO to CO2 and NO to NO2, with a chain length of 300 ± 60. This allows the atmospheric ClOx content to be measured under ambient conditions with a detection limit of better than 1 ppt. In parallel peroxy radicals are indicated with a chain length of 160 ± 15. Chemical amplification is not specific and does not indicate which radical chain it is seeing. Identification relies solely on plausibility. During the ARCtic Tropospheric Ozone Chemistry (ARCTOC) campaign in spring 1995 and 1996 the CA technique was used at Ny-Ålesund. ClOx at mixing ratios of up to 2 ppt were found in the boundary layer under certain conditions. The low concentrations of ClOx indicate that the arctic boundary ozone depletion is mainly driven by bromine.  相似文献   

5.
The seasonal and diurnal variations of ozone mixing ratios have been observed at Niwot Ridge. Colorado. The ozone mixing ratios have been correlated with the NO x (NO+NO2) mixing ratios measured concurrently at the site. The seasonal and diurnal variations in O3 can be reasonably well understood by considering photochemistry and transport. In the winter there is no apparent systematic diurnal variation in the O3 mixing ratio because there is little diurnal change of transport and a slow photochemistry. In the summer, the O3 levels at the site are suppressed at night due to the presence of a nocturnal inversion layer that isolated ozone near the surface, where it is destroyed. Ozone is observed to increase in the summer during the day. The increases in ozone correlate with increasing NO x levels, as well as with the levels of other compounds of anthropogenic origin. We interpret this correlation as in-situ or in-transit photochemical production of ozone from these precursors that are transported to our site. The levels of ozone recorded approach 100 ppbv at NO x mixing ratios of approximately 3 ppbv. Calculations made using a simple clean tropospheric chemical model are consistent with the NO x -related trend observed for the daytime ozone mixing ratio. However, the chemistry, which does not include nonmethane hydrocarbon photochemistry, underestimates the observed O3 production.  相似文献   

6.
The inability to explain the observedoxygen suppression of chlorine photosensitized ozoneloss remains a gap in our understanding of thephotochemistry responsible for depletion of thestratospheric ozone layer. It has been suggested thatthe presence of a weakly bound ClO·O2complexcould explain this effect. The existence of thiscomplex would alter the chlorine budget of thestratosphere, perhaps reducing the chlorine availablefor catalytic ozone destruction. On the other hand,the chemistry of ClO·O2 provides two newpathwaysfor ClO dimer formation, which could increase the rateof catalytic ozone loss. In this paper, we constrainthe kinetic rate system of ClO·O2 tomatch themeasured Cly budget. It is shown thatClO·O2cannot be both fairly stable and rapidly form the ClOdimer, or the resulting partitioning of chlorinebecomes incompatible with observations of both ClO andtotal available chlorine. These constraints allow thateither: (1) the ClO·O2 is fairly stable,but doesnot significantly enhance ClO dimer formation andtherefore has a negligible effect on ozone loss rates,or (2) the ClO·O2 complex is only veryweaklystable, but does rapidly form the ClO dimer, andtherefore can influence stratospheric ozone depletion.Even at the ClO·O2 mixing ratios allowedunderthe assumption of weak stability, 0.1 to 0.2 ppbv,significant ozone loss rate enhancements werecalculated. Of course, the chlorine budget constraintalso allows for a thirdpossibility; that ClO·O2 is neither verystablenor forms Cl2O2 very rapidly. Measuredlimits on the reaction rates for ClO·O2to form the ClO dimer would greatly aid the resolution of thisissue. Since the uncertainties aboutClO·O2chemistry are so large, a potential role forClO·O2 in stratospheric ozone loss cannotbe ruled out at this time.  相似文献   

7.
Abstract

To evaluate future climate change in the middle atmosphere and the chemistry–climate interaction of stratospheric ozone, we performed a long-term simulation from 1960 to 2050 with boundary conditions from the Intergovernmental Panel on Climate Change A1B greenhouse gas scenario and the World Meteorological Organization Ab halogen scenario using the chemistry–climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC). In addition to this standard simulation we performed five sensitivity simulations from 2000 to 2050 using the rerun files of the simulation mentioned above. For these sensitivity simulations we used the same model setup as in the standard simulation but changed the boundary conditions for carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone-depleting substances (ODS). In the first sensitivity simulation we fixed the mixing ratios of CO2, CH4, and N2O in the boundary conditions to the amounts for 2000. In each of the four other sensitivity simulations we fixed the boundary conditions of only one of CO2, CH4, N2O, or ODS to the year 2000.

In our model simulations the future evolution of greenhouse gases leads to significant cooling in the stratosphere and mesosphere. Increasing CO2 mixing ratios make the largest contributions to this radiative cooling, followed by increasing stratospheric CH4, which also forms additional H2O in the upper stratosphere and mesosphere. Increasing N2O mixing ratios makes the smallest contributions to the cooling. The simulated ozone recovery leads to warming of the middle atmosphere.

In the EMAC model the future development of ozone is influenced by several factors. 1) Cooler temperatures lead to an increase in ozone in the upper stratosphere. The strongest contribution to this ozone production is cooling due to increasing CO2 mixing ratios, followed by increasing CH4. 2) Decreasing ODS mixing ratios lead to ozone recovery, but the contribution to the total ozone increase in the upper stratosphere is only slightly higher than the contribution of the cooling by greenhouse gases. In the polar lower stratosphere a decrease in ODS is mainly responsible for ozone recovery. 3) Higher NOx and HOx mixing ratios due to increased N2O and CH4 lead to intensified ozone destruction, primarily in the middle and upper stratosphere, from additional NOx; in the mesosphere the intensified ozone destruction is caused by additional HOx. In comparison to the increase in ozone due to decreasing ODS, ozone destruction caused by increased NOx is of similar importance in some regions, especially in the middle stratosphere. 4) In the stratosphere the enhancement of the Brewer-Dobson circulation leads to a change in ozone transport. In the polar stratosphere increased downwelling leads to additional ozone in the future, especially at high northern latitudes. The dynamical impact on ozone development is higher at some altitudes in the polar stratosphere than the ozone increase due to cooler temperatures. In the tropical lower stratosphere increased residual vertical upward transport leads to a decrease in ozone.  相似文献   

8.
利用南京地面站点2016—2017年黑碳气溶胶(Black Carbon, BC)和臭氧(O_3)逐小时观测资料,对比分析了不同季节BC与近地面O_3的关系。结果表明,高BC(高于平均值)影响下的O_3质量浓度值明显比低BC(低于平均值)影响下的O_3质量浓度值低,这种抑制作用在秋冬季明显高于春夏季,且BC与O_3的负相关性在秋冬季显著高于春夏季,而PM_(2.5)与O_3的负相关性不显著。利用WRF-Chem模式,对2017年12月个例开展BC反馈效应对O_3影响的数值模拟,结果再次证实BC对O_3存在负反馈影响。其影响机制是:BC可通过抑制边界层发展,使近地面NO_x积聚,从而减少臭氧的化学生成(VOCs控制区);BC可通过抑制边界层垂直湍流交换,减少边界层上部高O_3向下的湍流输送,从而减少近地面O_3;BC可通过减小近地面风速,减少O_3的平流输入,从而减少地面O_3。不同个例的主要控制因子不同。  相似文献   

9.
As part of the LBA-CLAIRE-98 experiment, ground level atmosphericconcentrations of O3, CO, hydroperoxides and organic acids weremeasured in the rainforest region in Surinam. Measurements of CO andO3 were also made at a coastal site.The results suggest that a significant consumption of `boundary layer' ozoneoccurs over the forested region of Surinam, with an estimated net ozoneconsumption of about 5% hr–1 during daytime. Thiswould be mainly explained by a low photochemical production and high drydeposition to the forest vegetation. Compared to other tropical sites, lowerlevels of H2O2 were observed at the rainforest site,with an average boundary layer concentration of 0.55± 0.2 nmolmol–1. Also acetic and formic acids showed relatively lowaverage boundary layer mixing ratios; 1.1± 0.4 nmolmol–1 and 1.4± 0.5 nmol mol–1,respectively. Significant correlations were found between both acids andbetween the acids and hydrogen peroxide, suggesting an atmospheric source forthe acids.From the available observations we discuss possible implications of ourmeasurements for the O3, HO2, and NOx budgetsand concentrations in the boundary layer. We conclude that, despite the highsolar irradiation, relatively low levels of O3,H2O2, HCOOH and CH3COOH are observed in theboundary layer of the rainforest of Surinam, probably due to low levels ofNOx and high levels of VOCs, which leads to loss of OH andHO2 radicals. Additionally, high deposition rates of these gasesoccur to the forest vegetation.  相似文献   

10.
A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the mesoscale evolution of the daily cycle of CO2 and related tracers in the atmospheric boundary layer (ABL) and its relation to ABL dynamics and nearby natural and anthropogenic sources and sinks. A 2-μm heterodyne Doppler differential absorption lidar, which combines measurements of, (1) structure of the atmosphere, (2) radial velocity, and (3) CO2 differential absorption was a particularly unique element of the observational array. We analyse the differences in the diurnal cycle of CO, CO2, lidar reflectivity (a proxy for aerosol content) and H2O using the lidar, airborne measurements in the free troposphere and ground-based measurements made at two sites located few kilometres apart. We demonstrate that vertical mixing dominates the early morning drawdown of CO and aerosol content trapped in the former nocturnal layer but not the H2O and CO2 mixing ratio variations. Surface fluxes, vertical mixing and advection all contribute to the ABL CO2 mixing ratio decrease during the morning transition, with the relative importance depending on the rate and timing of ABL rise. We also show evidence that when the ABL is stable, small-scale (0.1-km vertical and 1-km horizontal) gradients of CO2 and CO are large. The results illustrate the complexity of inferring surface fluxes of CO2 from atmospheric budgets in the stable boundary layer.  相似文献   

11.
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12.
Continuous in-situ measurements of surface ozone (O3), carbon monoxide (CO) and oxides of nitrogen (NOx) were conducted at Udaipur city in India during April 2010 to March 2011. We have analyzed the data to investigate both diurnal and seasonal variations in the mixing ratios of trace gases. The diurnal distribution of O3 showed highest values in the afternoon hours and lower values from evening till early morning. The mixing ratios of CO and NOx showed a sharp peak in the morning hours but lowest in the afternoon hours. The daily mean data of O3, CO and NOx varied in the ranges of 5–51 ppbv, 145–795 ppbv and 3–25 ppbv, respectively. The mixing ratios of O3 were highest of 28 ppbv and lowest 19 ppbv during the pre-monsoon and monsoon seasons, respectively. While the mixing ratios of both CO and NOx showed highest and lowest values during the winter and monsoon seasons, respectively. The diurnal pattern of O3 is mainly controlled by the variations in photochemistry and planetary boundary layer (PBL) depth. On the other hand, the seasonality of O3, CO and NOx were governed by the long-range transport associated mainly with the summer and winter monsoon circulations over the Indian subcontinent. The back trajectory data indicate that the seasonal variations in trace gases were caused mainly by the shift in long-range transport pattern. In monsoon season, flow of marine air and negligible presence of biomass burning in India resulted in lowest O3, CO and NOx values. The mixing ratios of CO and NOx show tight correlations during winter and pre-monsoon seasons, while poor correlation in the monsoon season. The emission ratio of ?CO/?NOx showed large seasonal variability but values were lower than those measured over the Indo Gangetic Plains (IGP). The mixing ratios of CO and NOx decreased with the increase in wind speed, while O3 tended to increase with the wind speed. Effects of other meteorological parameters in the distributions of trace gases were also noticed.  相似文献   

13.
Summary Vertical profiles of H2O, CO2, O3, NO and NO2 were measured during the Hartheim Experiment (HartX) to develop and calibrate a multi-layer resistance model to estimate deposition and emission of the cited gaseous species. The meteorological and gas concentration data were obtained with a 30 m high telescopic mast with 7 gas inlets located at 5 m intervals and meteorological sensors at 5, 15 and 30 m above ground; a complete gas profile was obtained every 9 min 20 s. Measured profiles were influenced by several exchange processes, namely evapotranspiration, dewfall, assimilation of CO2 in the tree crowns, soil respiration, deposition of NO2 and O3 to the soil and advection of NOx from the nearby highway. Surprisingly, no decrease in O3 concentration was observed in the crown layer during daytime, probably due to the relatively low density of foliage elements and strong turbulent mixing.The advantage of measuring in-canopy profiles is that turbulent exchange coefficients need not be estimated as a prerequisite to obtaining vertical flux estimates. In recent years, flux-gradient relationships in canopies have been subject to many criticisms. If fluxes are calculated at several heights considering only the transfers between the turbulent air and the interacting surfaces at a certain height, and those fluxes are then integrated vertically in a subsequent step, then exchange estimates (deposition or emission) can be obtained independent of turbulent exchange conditions.Typical estimated deposition velocities calculated for a 3-day period are between 4 and 10 mm/s for NO2 and about 4–9 mm/s for O3 (day and night values respectively). This leads to deposition rates of about 20–40 ng N/m2s for NO2 and about 30–40 mg O3/m2 deposited daily under the conditions encountered during HartX. Sensitivity tests done with the best available and most realistic values for model parametrization have shown that sensitivity is large with respect to the soil and cuticula resistances as well as for gas-phase ozone destruction and that more research is required to describe the effectiveness of cuticula and soil in modifying sink characteristics for NO2 and O3.With 12 Figures  相似文献   

14.
The paper presents a coupled chemical-radiative one-dimensional model which is used to assess the steady-state and time-dependent composition and temperature changes in relation to the release in the atmosphere of chemicals such as CO2, N2O, CH4, NO x and chlorofluorocarbons.The model indicates that a doubling in CO2 leads to an increase in temperature of 12.7 K near the stratopause and to an increase in total ozone of 3.3% with a local enhancement of 17% at 40 km altitude. Additional release of N2O leads to an ozone reduction in the middle stratosphere. The reduction in the ozone column is predicted to be equal to 8.8% when the amount of N2O is doubled. The chemical effect of CH4 on ozone is particularly important in the troposphere. A doubling in the mixing ratio of this gas enhances the O3 concentration by 11% at 5 km. The predicted increase of the ozone column is equal to 1.4%. A constant emission of CFCl3 (230 kT/yr) and CF2Cl2 (300 kT/yr) leads to a steady-state reduction in the ozone column of 1.9% compared to the present-day situation. The effect of some uncertainties in the chemical scheme as well as the impact of a high chlorine perturbation are briefly discussed.Finally the results of a time dependent calculation assuming a realistic scenario for the emission of chemical species are presented and analyzed.  相似文献   

15.
Measurements of NOx,y were made at Alert, Nunavut, Canada (82.5° N, 62.3° W) during surface layer ozone depletion events. In spring 1998, depletion events were rare and occurred under variable actinic flux, ice fog, and snowfall conditions. NOy changed by less than 10% between normal, partially depleted, and nearly completely depleted ozone air masses. The observation of a diurnal variation in NOx under continuous sunlight supports a source from the snowpack but with rapid conversion to nitrogen reservoirs that are primarily deposited to the surface or airborne ice crystals. It was unclear whether NOx was reduced or enhanced in different stages of the ozone depletion chemistry because of variations in solar and ambient conditions. Because ozone was depleted from 15–20 ppbv to less than 1 ppbv in just over a day in one event it is apparent that the surface source of NOx did not grossly inhibit the removal of ozone. In another case ozone was shown to be destroyed to less than the 0.5 ppbv detection limit of the instrument. However, simple model calculations show that the rate of depletion of ozone and its final steady-state abundance depend sensitively on the strength of the surface source of NOx due to competition from ozone production involving NOx and peroxy radicals. The behavior of the NO/NO2 ratio was qualitatively consistent with enhanced BrO during the period of active ozone destruction. The model is also used to emphasize that the diurnal partitioning of BrOx during ozone depletion events is sensitive to even sub ppbv variations in O3.  相似文献   

16.
We have developed a simple, steady-state, one-dimensional second-order closure model to obtain continuous profiles of turbulent fluxes and mean concentrations of non-conserved scalars in a convective boundary layer without shear. As a basic tool we first set up a model for conserved species with standard parameterizations. This leads to formulations for profiles of the turbulent diffusivity and the ratio of temperature-scalar covariance to the flux of the passive scalar. The model is then extended to solving, in terms of profiles of mean concentrations and fluxes, the NO x –O3 triad problem. The chemical reactions involve one first-order reaction, the destruction of NO2 with decay time τ, and one second-order reaction, the destruction of NO and O3 with the reaction constant k. Since the fluxes of the sum concentrations of NO x = NO + NO2 and O3 + NO2 turn out to be constant throughout the boundary layer, the problem reduces to solving two differential equations for the concentration and the flux of NO2. The boundary conditions are the three surface fluxes and the fluxes at the top of the boundary layer, the last obtained from the entrainment velocity, and the concentration differences between the free troposphere and the top of the boundary layer. The equations are solved in a dimensionless form by using 1/(kτ) as the concentration unit, the depth h of the boundary layer as the length unit, the convective velocity scale w * as the velocity unit, and the surface temperature flux divided by w * as the temperature unit. Special care has been devoted to the inclusion of the scalar–scalar covariance between the concentrations of O3 and NO. Sample calculations show that the fluxes of the reactive species deviate significantly from those of non-reactive species. Further, the diffusivities, defined by minus the flux divided by the concentration gradient may become negative for reactive species in contrast to those of non-reactive species, which in the present model are never negative.  相似文献   

17.
The concentration of gas-phase peroxides has been measured almost continuously at the Cape Grim baseline station (41° S) over a period of 393 days (7702 h of on-line measurements) between February 1991 and March 1992. In unpolluted marine air a distinct seasonal cycle in concentration was evident, from a monthly mean value of>1.4 ppbv in summer (December) to <0.2 ppbv in winter (July). In the summer months a distinct diurnal cycle in peroxides was also observed in clean marine air, with a daytime build-up in concentration and decay overnight. Both the seasonal and diurnal cycles of peroxides concentration were anticorrelated with ozone concentration, and were largely explicable using a simple photochemical box model of the marine boundary layer in which the central processes were daytime photolytic destruction of ozone, transfer of reactive oxygen into the peroxides under the low-NOx ambient conditions that favour self-reaction between peroxy radicals, and continuous heterogeneous removal of peroxides at the ocean surface. Additional factors affecting peroxides concentrations at intermediate timescales (days to a week) were a dependence on air mass origin, with air masses arriving at Cape Grim from higher latitudes having lower peroxides concentrations, a dependence on local wind speed, with higher peroxides concentrations at lower wind speeds, and a systematic decrease in peroxides concentration during periods of rainfall. Possible physical mechanisms for these synoptic scale dependencies are discussed.  相似文献   

18.
Measurements of the sum of peroxy radicals [HO2 + RO2],NOx (NO + NO2) and NOy (the sum of oxidisednitrogen species) made at Mace Head, on the Atlantic coast of Ireland in summer 1996 and spring 1997 are presented. Together with a suite of ancillary measurements, including the photolysis frequencies of O3 O(1D)(j(O1D)) and NO2 (j(NO2)), the measured peroxy radicals are used to calculate meandailyozone tendency (defined as the difference of the in-situphotochemical ozone production and loss rates); these values are compared with values derived from the photochemical stationary state (PSS) expression. Although the correlation between the two sets of values is good, the PSS values are found to be significantly larger than those derived from the peroxy radical measurements, on average, in line with previous published work. Possible sources of error in these calculations are discussed in detail. The data are further divided up into five wind sectors, according to the instantaneous wind direction measured at the research station. Calculation of mean ozone tendencies by wind sector shows that ozone productivity was higher during spring (April–May) 1997 than during summer (July–August) 1996across all airmasses, suggesting that tropospheric photochemistry plays an important role in the widely-reported spring ozone maximum in the Northern Hemisphere. Ozone tendencies were close to zero for the relatively unpolluted south-west, west and north-west wind sectors in the summer campaign, whereas ozone productivity was greatest in the polluted south-east sector for both campaigns. Daytime weighted average ozone tendencies were +(0.3± 0.1) ppbv h–1 for summer 1996 and +(1.0± 0.5) ppbvh–1 for spring 1997. These figures reflect the higher mixing ratios of ozone precursors in spring overall, as well as the higher proportion of polluted air masses from the south-east arriving at the site during the spring campaign. The ozone compensation point, where photochemical ozone destruction and production processes are in balance, is calculated to be ca. 14 pptv NO for both campaigns.  相似文献   

19.
Measurements of NO2, HCHO, and H2O2 were made by the highly specific method of mid infra-red absorption spectroscopy using tunable diode lasers (TDLAS) during the 1988 Polarstern expedition. The TDLAS data are compared to those obtained during the cruise using less direct methods. Southern Hemisphere NO2 levels suggest nett photochemical destruction of O3 in the boundary layer. Northern Hemisphere HCHO averaged 0.47±0.2 ppbv; the HCHO measurements are used in a simple calculation to estimate OH noontime maxima of 3–6×106 cm-3.  相似文献   

20.
A 2-D global chemistry-transport model is set up in this paper.The model simulates the atmospheric ozone distributions well with specified dynamical conditions.The analysis of ozone variation mechanism shows that ozone is chemically in quasi-equilibrium except for the polar night region where the variation of ozone concentration is under the control of dynamical processes,that the oxygen atoms which produce ozone are mainly provided by the photolysis of O2 in the upper stratosphere and by the photolysis of NO2 in the lower stratosphere and the troposphere.and that the ozone is destroyed mainly by NOx:the reactions between NOx and O3 and the odd oxygen cycle contribute 80% to more than 90% of the ozone destruction.  相似文献   

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