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1.
The chemically induced ozone loss inside the Arctic vortex during the winter 1994/95 has been quantified by coordinated launches of over 1000 ozonesondes from 35 stations within the Match 94/95 campaign. Trajectory calculations, which allow diabatic heating or cooling, were used to trigger the balloon launches so that the ozone concentrations in a large number of air parcels are each measured twice a few days apart. The difference in ozone concentration is calculated for each pair and is interpreted as a change caused by chemistry. The data analysis has been carried out for January to March between 370 K and 600 K potential temperature. Ozone loss along these trajectories occurred exclusively during sunlit periods, and the periods of ozone loss coincided with, but slightly lagged, periods where stratospheric temperatures were low enough for polar stratospheric clouds to exist. Two clearly separated periods of ozone loss show up. Ozone loss rates first peaked in late January with a maximum value of 53 ppbv per day (1.6 % per day) at 475 K and faster losses higher up. Then, in mid-March ozone loss rates at 475 K reached 34 ppbv per day (1.3 % per day), faster losses were observed lower down and no ozone loss was found above 480 K during that period. The ozone loss in hypothetical air parcels with average diabetic descent rates has been integrated to give an accumulated loss through the winter. The most severe depletion of 2.0 ppmv (60 %) took place in air that was at 515 K on 1 January and at 450 K on 20 March. Vertical integration over the levels from 370 K to 600 K gives a column loss rate, which reached a maximum value of 2.7 Dobson Units per day in mid-March. The accumulated column loss between 1 January and 31 March was found to be 127 DU (36 %).  相似文献   

2.
The total ozone reduction in the Arctic during the winters of 1993/94 and 1994/95 has been evaluated using the ground-based total ozone measurements of five SAOZ spectrometers distributed in the Arctic and from number density profiles of a balloon-borne version of the instrument. The ozone change resulting from transport has been removed using a 3D Chemistry Transport Model (CTM) run without chemistry. A cumulative total ozone depletion at the end of winter in March of 18% ± 4% in 1994 and of 32% ± 4% in 1995 was observed within the polar vortex, and of 15% ± 4% in both years outside the vortex. This evaluation is not sensitive to the vertical transport in the model. The periods, locations and altitudes at which ozone loss occurred were tightly connected to temperatures lower than NAT condensation temperature. The maximum loss was observed at 50 hPa in 1994 and lower, 60-80 hPa, in 1995. Half of the depletion in 1994 and three quarters in 1995 occurred during the early winter, showing that a late final warming is not a prerequisite for large ozone destruction in the northern hemisphere. The timing, the geographical location and the altitude of the ozone losses are well captured by the 3D CTM photochemical model using current chemistry, but its amplitude at low sun during the early winter, is underestimated. The model simulations also capture the early season reductions observed outside the vortex. This suggests that the losses occurred in situ in the early winter, when low temperatures are frequent, and not later in March, when ozone is most reduced inside the vortex, which would be the case if leakage from the vortex was the cause of the depletion.  相似文献   

3.
Ozone evolution and diabatic descent in the Arctic polar vortex in winter 1995/1996 was studied with a newly developed diabatic trajectory–chemistry model (DTCM). To study the chemical and dynamic evolution of the species in the polar vortex, 400 diabatic trajectories were calculated in the vortex core and edge region by using three-dimensional (3-D) wind data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). The averaged diabatic descending motion and ozone behavior were obtained for particles started from the core and from the edge region of the vortex. The difference in ozone-loss rates as well as the difference in descending rates between the vortex core and the vortex-edge region was not statistically significant. The average cumulative ozone loss of 65 ± 16% in the vortex core obtained from the model calculations was consistent with the estimates obtained with a different method (Match experiment). The model results for the vortex core were compared with those obtained using trajectories with the vertical winds calculated on the basis of radiative cooling rates as used by the SLIMCAT 3-D chemical transport model. Although the trajectories based on cooling rates exhibited lower descending rates than those based on 3-D analyzed wind data, the ozone behavior was similar for both types of trajectory. Ozonesonde data from two stations (Ny-Alesund in the vortex core and Yakutsk in the vortex edge) were compared with the model results. For Lagrangian estimation of the ozone loss at these stations, the descending rates obtained by the diabatic trajectory calculations were used. Good agreements were obtained between the model results and observations for both the vortex core and edge region. These results suggest that strong ozone depletion occurred not only in the core, but also in the edge region of the vortex, and that air masses from the mid-latitudes did not appreciably affect the degree of ozone depletion in this winter–spring period. The sensitivity of the model to different descending rates and to the presence of large nitric acid trihydrate (NAT) particles was also examined.  相似文献   

4.
Local ozone production and loss rates for the arctic free troposphere (58–85° N, 1–6 km, February–May) during the TroposphericOzone Production about the Spring Equinox (TOPSE) campaign were calculated using a constrained photochemical box model. Estimates were made to assess the importance of local photochemical ozone production relative to transport in accounting for the springtime maximum in arctic free tropospheric ozone. Ozone production and loss rates from our diel steady-state box model constrained by median observations were first compared to two point box models, one run to instantaneous steady-state and the other run to diel steady-state. A consistent picture of local ozone photochemistry was derived by all three box models suggesting that differences between the approaches were not critical. Our model-derived ozone production rates increased by a factor of 28 in the 1–3 km layer and a factor of 7 in the 3–6 kmlayer between February and May. The arctic ozone budget required net import of ozone into the arctic free troposphere throughout the campaign; however, the transport term exceeded the photochemical production only in the lower free troposphere (1–3 km) between February and March. Gross ozone production rates were calculated to increase linearly with NOx mixing ratiosup to 300 pptv in February and for NOx mixing ratios up to 500 pptv in May. These NOx limits are an order of magnitude higher thanmedian NOx levels observed, illustrating the strong dependence ofgross ozone production rates on NOx mixing ratios for the majority of theobservations. The threshold NOx mixing ratio needed for netpositive ozone production was also calculated to increase from NOx 10pptv in February to 25 pptv in May, suggesting that the NOx levels needed to sustain net ozone production are lower in winter than spring. This lower NOx threshold explains how wintertime photochemical ozone production can impact the build-up of ozone over winter and early spring. There is also an altitude dependence as the threshold NOx neededto produce net ozone shifts to higher values at lower altitudes. This partly explains the calculation of net ozone destruction for the 1–3 km layerand net ozone production for the 3–6 km layer throughout the campaign.  相似文献   

5.
Ozone measurements, performed since 1987, at the Swedish TOR/EUROTRACstation Åreskutan (lat. 63.4° N, long. 13.1° E, 1250 m abovesea level) are analyzed. The annual average ozone concentration at the sitehas increased by about 0.4 ppbv (1%) per year during the period1987–1994. The corresponding trends for individual months show adecrease during April–September and an increase during the rest of theyear. The ozone budget at Åreskutan has been investigated using backtrajectories of the air parcels, and the cosmogenic radionuclide7Be as a tracer of stratospheric air. From a simple diagnosticmodel, it is estimated that the contribution of stratospheric ozone to theconcentrations measured at Åreskutan is 5 ppbv (or 14% of themeasured values) on average, reaching a maximum of 23 ppbv (50%),during the episodes of direct stratospheric influence. In spring, thestratospheric contribution to ozone budget at Åreskutan is at itsmaximum, and approximately equal to the net photochemical ozone productionin the air mass affecting the site, whereas in winter, it is compensated byozone chemical sink during the transport of air masses from pollutedEuropean regions, to Scandinavia.  相似文献   

6.
We have investigated the effect of the export of Arctic ozone loss, or`dilution', on mid-latitude ozone depletion during the 1990s, and its relation tointerannual meteorological variability. A stratospheric chemical-transport modelincorporated a simple gas-phase ozone scheme with the addition of a parameterisation ofpolar depletion which depended only on temperature and duration of sunlight. Themodel was forced with the U.K. Meteorological Office analyses from 1991 to 1999 covering eight Northern Hemisphere winters. The modelled Arctic ozone column losses wereabout half the magnitude of those in the Antarctic and showed a considerablevariation from year to year. The northern middle latitudes (40°–60° N)were mainly affected through dilution and experienced a variable 5–20%depletion. Year-round there is a depletion of about 1% in northern middle latitudes due toactivation at the pole but there is no evidence that this depletion increases with timeduring this integration. A series of inert tracer experiments for the winters from 1996 to 1999 showed that the dilution occurs primarily at the 560 K and 465 K isentropic levels where up to 30% of the airoriginating northward of 67° N on 1 March is found at 47° N later in spring. Thestrength and persistence of the Arctic vortex were crucial in determining the severity and the timing of the ozone dilution every year by influencing, respectively, the magnitude of the high-latitude depletion and the effectiveness of mixing to lower latitudes. This spring dilution was correlated with the winter/spring planetary wave activity indicating the important role of dynamical processes in regulating the polar-driven mid-latitude ozone depletion.  相似文献   

7.
Estimates of the Chemical Budget for Ozone at Waliguan Observatory   总被引：6，自引：0，他引：6  
Waliguan Observatory (WO) is an in-land Global Atmosphere Watch (GAW) baseline station on the Tibetan plateau. In addition to the routine GAW measurement program at WO, measurements of trace gases, especially ozone precursors, were made for some periods from 1994 to 1996. The ozone chemical budget at WO was estimated using a box model constrained by these measured trace gas concentrations and meteorological variables. Air masses at WO are usually affected by the boundary layer (BL) in the daytime associated with an upslope flow, while it is affected by the free troposphere (FT) at night associated with a downslope flow. An anti-relationship between ozone and water vapor concentrations at WO is found by investigating the average diurnal cycle pattern of ozone and water vapor under clear sky conditions. This relationship implies that air masses at WO have both the FT and BL characteristics. Model simulations were carried out for clear sky conditions in January and July of 1996, respectively. The chemical characteristics of mixed air masses (MC) and of free tropospheric air masses (FT) at WO were investigated. The effects of the variation in NOx and water vapor concentrations on the chemical budget of ozone at WO were evaluated for the considered periods of time. It was shown that ozone was net produced in January and net destroyed in July for both FT and MC conditions at WO. The estimated net ozone production rate at WO was –0.1 to 0.4 ppbv day–1 in FT air of January, 0.0 to 1.0 ppbv day–1 in MC air of January, –4.9 to –0.2 ppbv day–1 in FT air of July, and –5.1 to 2.1 ppbv day–1 in MC air of July.  相似文献   

8.
Simultaneousindependent measurements of NOy and NOx(NOx= NO + NO2) by high-sensitivitychemiluminescence systems and of PAN (peroxyacetylnitrate) and PPN (peroxypropionyl nitrate) by GC-ECDwere made at Spitsbergen in the Norwegian Arcticduring the first half year of 1994. The average mixingratio of the sum of PAN and PPN (denoted PANs)increased from around 150 pptv in early winter to amaximum of around 500 pptv in late March, whereasepisodic peak values reached 800 pptv. This occurredsimultaneously with a maximum in ozone which increasedto 45–50 ppbv in March–April. The average NOxmixing ratio was 27 pptv and did not show any cyclethrough the period. The NOy mixing ratio showeda maximum in late March, while the difference betweenNOy and PAN decreased during spring. This is anindication of the dominance of PAN in the NOybudget in the Arctic, but possible changes in theefficiency of the NOy converter could alsocontribute to this. Although most PAN in theArctic is believed to be due to long range transport,the observations indicate local loss and formationrates of up to 1–2 pptv h-1 in April–May.Measurements of carbonyl compounds suggest thatacetaldehyde was the dominant, local precursor ofPAN.Now at 1.  相似文献   

9.
Detailed studies have been made of the behaviour of gases and radicals involved in the production of oxidants at the Weybourne Atmospheric Observatory in both summertime and wintertime conditions. In June 1995 the range of meteorological conditions experienced varied such that ozone destruction was observed in clean northerly air flows reaching Weybourne down the North Sea from the Arctic, and ozone production was observed in varying degrees in air with different loadings of nitrogen oxides and other precursors. The transition point for ozone destruction to ozone production occurred at a nitric oxide concentration of the order of 50 pptv. Plumes of polluted air from various urban areas in the U.K. were experienced in the June campaign at Weybourne. Quantitative studies of ozone production in a plume from the Birmingham conurbation on 18 June 1995 showed that the measurement of ozone production agreed well with calculated production rates from the product of the nitric oxide and peroxy radical concentrations (r2=0.9). In wintertime conditions (October–November 1994) evidence was also found for oxidant production, defined as the sum of O3+NO2. At this time of year the peroxy radical concentrations (RO2) were much lower than observed in the summertime and the nitric oxide (NO) was much higher. There was still sufficient RO2 during the day, however, for a slow accumulation of oxidant. Confirmatory evidence for this comes from the diurnal co-variance of (O3+NO2) with PAN, an excellent tracer of tropospheric photochemistry. The same type of covariance occurs in summer between PAN and ozone. The results obtained in these series of measurements are pertinent to understanding the measures necessary to control production of regional photochemical air pollution, and to the production of ozone throughout the northern hemisphere in winter.  相似文献   

10.
Measurements of NOx (NO +NO2) and the sum of reactive nitrogenconstituents, NOy, were made near the surface atAlert (82.5°N), Canada during March and April1998. In early March when solar insolation was absentor very low, NOx mixing ratios were frequentlynear zero. After polar sunrise when the sun was abovethe horizon for much or all of the day a diurnalvariation in NOx and NOy was observed withamplitudes as large as 30–40 pptv. The source ofactive nitrogen is attributed to release from the snowsurface by a process that is apparently sensitized bysunlight. If the source from the snowpack is a largescale feature of the Arctic then the diurnal trendsalso require a competing process for removal to thesurface. From the diurnal change in the NO/NO2ratio, mid-April mixing ratios for the sum of peroxyand halogen oxide radicals of 10 pptv werederived for periods when ozone mixing ratios were inthe normal range of 30–50 ppbv. Mid-day ozoneproduction and loss rates with the active nitrogensource were estimated to be 1–2 ppbv/day and in nearbalance. NOy mixing ratios which averaged only295±66 pptv do not support a large accumulation inthe high Arctic surface layer in the winter and springof 1998. The small abundance of NOy relative tothe elevated mixing ratios of other long-livedanthropogenic constituents requires that reactivenitrogen be removed to the surface during transport toor during residence within the high Arctic.  相似文献   

11.
Airborne measurements of stratospheric ozone and N2O from the SCIAMACHY (Scanning Imaging Absorption Spectrometer) Validation and Utilization Experiment (SCIA-VALUE) are presented. The campaign was conducted in September 2002 and February–March 2003. The Airborne Submillimeter Radiometer (ASUR) observed stratospheric constituents like O3 and N2O, among others, spanning a latitude from 5°S to 80°N during the survey. The tropical ozone source regions show high ozone volume mixing ratios (VMRs) of around 11 ppmv at 33 km altitude, and the altitude of the maximum VMR increases from the tropics to the Arctic. The N2O VMRs show the largest value of 325 ppbv in the lower stratosphere, indicating their tropospheric origin, and they decrease with increasing altitude and latitude due to photolysis. The sub-tropical and polar mixing barriers are well represented in the N2O measurements. The most striking seasonal difference found in the measurements is the large polar descent in February–March. The observed features are interpreted with the help of SLIMCAT and Bremen Chemical Transport Model (CTMB) simulations. The SLIMCAT simulations are in good agreement with the measured O3 and N2O values, where the differences are within 1 ppmv for O3 and 15 ppbv for N2O. However, the CTMB simulations underestimate the tropical middle stratospheric O3 (1–1.5 ppmv) and the tropical lower stratospheric N2O (15–30 ppbv) measurements. A detailed analysis with various measurements and model simulations suggests that the biases in the CTMB simulations are related to its parameterised chemistry schemes.  相似文献   

12.
Simulations of polar ozone losses were performed using the three-dimensional high-resolution (1∘ × 1∘) chemical transport model MIMOSA-CHIM. Three Arctic winters 1999–2000, 2001–2002, 2002–2003 and three Antarctic winters 2001, 2002, and 2003 were considered for the study. The cumulative ozone loss in the Arctic winter 2002–2003 reached around 35% at 475 K inside the vortex, as compared to more than 60% in 1999–2000. During 1999–2000, denitrification induces a maximum of about 23% extra ozone loss at 475 K as compared to 17% in 2002–2003. Unlike these two colder Arctic winters, the 2001–2002 Arctic was warmer and did not experience much ozone loss. Sensitivity tests showed that the chosen resolution of 1∘ × 1∘ provides a better evaluation of ozone loss at the edge of the polar vortex in high solar zenith angle conditions. The simulation results for ozone, ClO, HNO3, N2O, and NO y for winters 1999–2000 and 2002–2003 were compared with measurements on board ER-2 and Geophysica aircraft respectively. Sensitivity tests showed that increasing heating rates calculated by the model by 50% and doubling the PSC (Polar Stratospheric Clouds) particle density (from 5 × 10−3 to 10−2 cm−3) refines the agreement with in situ ozone, N2O and NO y levels. In this configuration, simulated ClO levels are increased and are in better agreement with observations in January but are overestimated by about 20% in March. The use of the Burkholder et al. (1990) Cl2O2 absorption cross-sections slightly increases further ClO levels especially in high solar zenith angle conditions. Comparisons of the modelled ozone values with ozonesonde measurement in the Antarctic winter 2003 and with Polar Ozone and Aerosol Measurement III (POAM III) measurements in the Antarctic winters 2001 and 2002, shows that the simulations underestimate the ozone loss rate at the end of the ozone destruction period. A slightly better agreement is obtained with the use of Burkholder et al. (1990) Cl2O2 absorption cross-sections.  相似文献   

13.
Zenith sky observations of O3, NO2, OClO and BrO are reported, which were performed at Kiruna (67.9°N, 21.1°E) within the SESAME winters 1993/1994 and 1994/95. For both winters large total amounts of OClO were observed inside the polar vortex at twilight, indicating the degree and the temporal variation of the halogen activation of the polar stratosphere. Occasionally OClO could also be observed outside the polar vortex, most likely due to export of halogen activated vortex air masses into the ambient stratosphere. BrO could also be detected in winter 1994/95, with the largest slant column amounts (5·1014/cm2) occuring in the polar vortex in mid-winter. Similar abundances of stratospheric BrO were observed at dusk and dawn, for both, air masses inside and outside the vortex. This observation is in reasonable agreement with previous studies on stratospheric BrO (observations and models) of Wahner et al. (1992), Arpag et al. (1994), Krug et al. (1996), and Lary et al. (1996a,b), but partly in disagreement with those of Solomon et al. (1989), Fish et al. (1995), and Sessler et al. (1996).  相似文献   

14.
In the present study, an attempt has been made to examine the governing photochemical processes of surface ozone (O3) formation in rural site. For this purpose, measurements of surface ozone and selected meteorological parameters have been made at Anantapur (14.62°N, 77.65°E, 331 m asl), a semi-arid zone in India from January 2002 to December 2003. The annual average diurnal variation of O3 shows maximum concentration 46 ppbv at noon and minimum 25 ppbv in the morning with 1σ standard deviation. The average seasonal variation of ozone mixing ratios are observed to be maximum (about 60 ppbv) during summer and minimum (about 22 ppbv) in the monsoon period. The monthly daytime and nighttime average surface ozone concentration shows a maximum (55 ± 7 ppbv; 37 ± 7.3 ppbv) in March and minimum (28 ± 3.4 ppbv; 22 ± 2.3 ppbv) in August during the study period. The monthly average high (low) O3 48.9 ± 7.7 ppbv (26.2 ± 3.5 ppbv) observed at noon in March (August) is due to the possible increase in precursor gas concentration by anthropogenic activity and the influence of meteorological parameters. The rate of increase of surface ozone is high (1.52 ppbv/h) in March and lower (0.40 ppbv/h) in July. The average rate of increase of O3 from midnight to midday is 1 ppbv/h. Surface temperature is highest (43–44°C) during March and April months leading to higher photochemical production. On the other hand, relative humidity, which is higher during the rainy season, shows negative correlation with temperature and ozone mixing ratio. It can be seen that among the two parameters are measured, correlation of surface ozone with wind speed is better (R 2=0.84) in compare with relative humidity (R 2=0.66).  相似文献   

15.
The effects of deep convection on the potential for forming ozone (ozone production potential) in the free troposphere have been simulated for regions where the trace gas composition is influenced by biomass burning. Cloud dynamical and photochemical simulations based on observations in 1980 and 1985 Brazilian campaigns form the basis of a sensitivity study of the ozone production potential under differing conditions. The photochemical fate of pollutants actually entrained in a cumulus event of August 1985 during NASA/GTE/ABLE 2A (Case 1) is compared to photochemical ozone production that could have occurred if the same storm had been located closer to regions of savanna burning (Case 2) and forest burning (Case 3). In each case studied, the ozone production potential is calculated for a 24-hour period following convective redistribution of ozone precursors and compared to ozone production in the absence of convection. In all cases there is considerably more ozone formed in the middle and upper troposphere when convection has redistributed NOx, hydrocarbons and CO compared to the case of no convection.In the August 1985 ABLE 2A event, entrainment of a layer polluted with biomass burning into a convective squall line changes the free tropospheric cloud outflow column (5–13 km) ozone production potential from net destruction to net production. If it is assumed that the same cloud dynamics occur directly over regions of savanna burning, ozone production rates in the middle and upper troposphere are much greater. Diurnally averaged ozone production following convection may reach 7 ppbv/day averaged over the layer from 5–13 km-compared to typical free tropospheric concentrations of 25–30 ppbv O3 during nonpolluted conditions in ABLE 2A. Convection over a forested region where isoprene as well as hydrocarbons from combustion can be transported into the free troposphere leads to yet higher amounts of ozone production.  相似文献   

16.
Three independent methods have been used to sort the ozone, carbonmonoxide, and other radiatively important trace gases measured at Mace Head,Ireland, and thereby distinguish clean air masses transported over the NorthAtlantic from the more polluted air masses which have recently travelledfrom the European continent. Over the period April 1987–June 1995 theNorthern Hemisphere surface ozone baseline concentrations exhibited a meanconcentration of 34.8 ppb, with a small positive trend (+0.19 ppbyr-1), while the corresponding trend in air originating fromthe polluted European areas was negative (–0.39 ppbyr-1). Carbon monoxide measurements from March 1990 toDecember 1994 showed negative trends for both the unpolluted (–0.17ppb yr-1) and polluted data (–13.6 ppbyr-1). Overall the continent of Europe was shown to be a smallnet sink of 2.6 ppb for all occasions when European air was transported tothe North Atlantic.  相似文献   

17.
Summary An analysis of correlation coefficients for climatological data covering the period 1901–1994 or 1931–1994 for six locations in Switzerland has been made in order to highlight the relationships between temperature, precipitation (rain and snow) and snow in summer and in winter. The results show that colder summers tend to be associated with more precipitation, mainly in terms of the frequency of occurrence of precipitation, but also in terms of its abundancy. In winter, sites located at lower altitudes behave differently from those at higher elevations. At lower altitudes, warmer winters tend to be rainier and to have less snow (only a small part of winter precipitation falls in the form of snow). Above 1000–1500 m, correlations between temperature on the one hand, and precipitation or snow on the other, tend to be weaker than at lower elevations; warmer winters are associated with less snow but also with less precipitation in general, while the relationship between precipitation and snow is stronger.These results confirm that during cold periods of the past, such as Löbben Phase (1400 BC — 1230 BC) cold summers were probably linked to frequent and abundant precipitation. These conditions led to increased mortality as well as to population migrations. In terms of potential future global warming, if the current temperature/precipitation relationships remain unchanged, then warmer summers will likely be linked to a decrease in precipitation. Higher winter temperatures can be expected to lead to a general decrease of snow and to a decrease in precipitation, but only at higher elevations; warmer winters would conversely be associated with an increase in precipitation at lower altitudes.With 4 Figures  相似文献   

18.
In part two of this series of papers on the IMS model, we present the chemistry reaction mechanism usedand compare modelled CH4, CO, and O3 witha dataset of annual surface measurements. The modelled monthly and 24-hour mean tropospheric OH concentrationsrange between 5–22 × 105 moleculescm–3, indicating an annualaveraged OH concentration of about 10 × 105 moleculescm–3. This valueis close to the estimated 9.7 ± 0.6 × 105 moleculescm–3 calculated fromthe reaction of CH3CCl3 with OH radicals.Comparison with CH4 generally shows good agreementbetween model and measurements, except for the site at Barrow where modelledwetland emission in the summer could be a factor 3 too high.For CO, the pronounced seasonality shown in the measurements is generally reproduced by the model; however, the modelled concentrations are lower thanthe measurements. This discrepancy may due to lower the CO emission,especially from biomass burning,used in the model compared with other studies.For O3, good agreement between the model and measurements is seenat locations which are away from industrial regions. The maximum discrepancies between modelled results and measurementsat tropical and remote marine sites is about 5–10 ppbv,while the discrepancies canexceed 30 ppbv in the industrial regions.Comparisons in rural areas at European and American continental sites arehighly influenced by the local photochemicalproduction, which is difficult to model with a coarse global CTM.The very large variations of O3 at these locations vary from about15–25 ppbv in Januaryto 55–65 ppbv in July–August. The observed annual O3amplitude isabout 40 ppbv compared with about 20 ppbv in the model. An overall comparison of modelled O3 with measurements shows thatthe O3seasonal surface cycle is generally governed bythe relative importance of two key mechanisms that drivea springtime ozone maximum and asummertime ozone maximum.  相似文献   

19.
Gaseous formic and acetic acids in the atmosphere of Yokohama,Japan   总被引：1，自引：1，他引：0  
Gaseous formic acid (HCOOHg) and acetic acid (CH3COOHg) were measured every 30 minutes during a 10 hour daylight period in August, and a 24 hour period in October, 1990 in the urban atmosphere of Yokohama, Japan. An aqueous nebulizer sampler and ion-chromatography exclusion (ICE) were used for the measurements. In the August experiment (0800–1800 local time) the mean HCOOHg concentration was found to be 7.3±2.5 ppbv. The mean CH3COOHg concentration was 3.8±1.2 ppbv. In the 24 hour experiment in October, concentrations of both acids were lower between 0800–1800 than during the same time-period in August (mean HCOOHg=4.4±2.7 ppbv, mean CH3COOHg=1.4±0.5 ppbv). In October, concentrations of both acids were higher in daylight hours than at night; sporadic high HCOOHg concentrations were observed. In both experiments the ratio HCOOHg/CH3COOHg of individual samples was usually 2.0 (mean ratio of 2.0 in August, 3.1 in October).  相似文献   

20.
Vertical column abundances of HCl, ClONO2, HF and HNO3 have been obtained from infrared solar absorption measurements made at Aberdeen, UK (57°N, 2°W) during the periods January 13 1994 - May 8 1994 and November 23 1994 - April 19 1995. The measurements reveal the partitioning of inorganic chlorine (Cly) inside and outside the polar vortex during these two winter and spring periods. Stratospheric temperatures within the northern polar vortex during 1993/94 were not cold throughout January and most of February. The measurements reported here suggest that following a brief period of chlorine activation in late February and early March, the active chlorine within the vortex recovered rapidly to form ClONO2 resulting in in-vortex ClONO2 columns of 7 × 1015 molecules cm-2. In contrast, measurements during January 1995 suggest extensive invortex activation with in-vortex HCl + ClONO2 as low as 3.6×1015 molecules cm-2. High day-to-day variability in the ClONO2 columns observed during February is evidence for the transport of ClONO2 rich air from high to mid latitudes during the late winter. The implications for mid latitude O3 loss are discussed. A preliminary comparison of the HCl, ClONO2, and HNO3 column data from winter 94/95 with a three-dimensional chemical transport model shows that the model generally reproduces well the day-to-day variability and absolute magnitude of the observed columns, especially for HNO3 outside of the vortex.  相似文献   

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