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1.
The manual harvest of sugar cane requires the burning of its foliage. This burning has strongly increased in Brazil after the National Alcohol Program was started which substituted automobile gasoline engines for alcohol engines. Presently, the source strength per unit area of this rural pollution is comparable to the well-known biomass burning source in Amazonia. The observed concentrations of CO and O3 in the rural area of the state of São Paulo during the 1988 burning season were twice as large as those reported from an aircraft experiment of 1985 for biomass burnings of the tropical rain forest. Results are reported from airplane measurements and from three fixed ground stations. Mixing ratios of ozone and carbon monoxide in the height range below 6 km are normally less than 40 and 100 ppbv, (parts per billion by volume), respectively, in the absence of burnings. A strong O3 and CO layer was observed during the burning period with peak concentrations of 80 ppbv of ozone and 580 ppbv of CO at about 2 km. The concentrations of CH4 and CO2 were also large, 1756 ppbv and 409 ppmv, respectively, at 1500 m. During the dry season period of the experiment, the ground based O3 average diurnal variations obtained at the rural sites were practically identical to the typical urban variation observed at São José dos Campos, with daytime ozone values between 45 and 60 ppbv. A second three-day airplane excursion to the surgar cane fields in the wet season of 1989 has produces results to be contrasted with the dry (burning) season of 1988 and 1989. Carbon monoxide concentrations were below 100 ppbv at all heights and ozone concentrations were around 30–40 ppbv. The maximum daytime concentrations at the ground station Bauru was 25 ppbv of O3, and at Jaboticabal it was 35 ppbv of O3, only one half of what was observed in the dry season.Universidade Estadual de São Paulo.  相似文献   

2.
Abstract

Carbonyl sulphide (OCS) is an important precursor of sulphate aerosols and consequently a key species in stratospheric ozone depletion. The SPectromètre InfraRouge d'Absorption à Lasers Embarqués (SPIRALE) and shortwave infrared (SWIR) balloon-borne instruments have flown in the tropics and in the polar Arctic, and ground-based measurements have been performed by the Qualité de l'Air (QualAir) Fourier Transform Spectrometer in Paris. Partial and total columns and vertical profiles have been obtained to study OCS variability with altitude, latitude, and season. The annual total column variation in Paris reveals a seasonal variation with a maximum in April–June and a minimum in November–January. Total column measurements above Paris and from SWIR balloon-borne instrument are compared with several MkIV measurements, several Network for the Detection of Atmospheric Composition Change (NDACC) stations, aircraft, ship, and balloon measurements to highlight the OCS total column decrease from tropical to polar latitudes. OCS high-resolution in situ vertical profiles have been measured for the first time in the altitude range between 14 and 30?km at tropical and polar latitudes. OCS profiles are compared with Atmospheric Chemistry Experiment (ACE) satellite measurements and show good agreement. Using the correlation between OCS and N2O from SPIRALE, the OCS stratospheric lifetime has been accurately determined. We find a stratospheric lifetime of 68?±?20 years at polar latitudes and 58?±?14 years at tropical latitudes leading to a global stratospheric sink of 49?±?14?Gg?S?y?1.  相似文献   

3.
Ozone loss rates from ozonesonde data reported in the Match experiments of winters 1994/95 and 1995/96 inside the Arctic polar vortex are compared with simulations of the same winters performed using the SLIMCAT 3D chemistry and transport model. For 1994/95 SLIMCAT reproduces the location and timing of the diagnosed ozone destruction, reaching 10 ppbv/sunlit hour in late January as observed. SLIMCAT underestimates the loss rates observed in February and March by 1–3 ppbv/sunlit hour. By the end of March, SLIMCAT ozone exceeds the observations by 25–35%. In January 1995 the ozonesonde-derived loss rates at levels above 525 K are not chemical in origin but due to poor conservation of air parcels. Correcting temperature biases in the model forcing data significantly improved the agreement between the model and observed ozone at the end of winter 1994/95, increasing ozone destruction in SLIMCAT in February and March. The SLIMCAT simulation of winter 1995/96 does not reproduce the maximum ozone loss rates diagnosed by Match of 13 ppbv/sunlit hour. Comparing the data for the two winters reveals that the SLIMCAT photochemistry is least able to reproduce observed losses at low temperatures or when low temperatures coincide with high solar zenith angles (SZA). When cold (T = 192 K), high SZA (90°)matches are excluded from the 1995/96 analysis, agreement between the diagnoses and SLIMCAT is better with ozone loss rates of up to 6 ppbv/sunlit hour. For the rest of the winter SLIMCAT consistently underestimates the Match rates of ozone loss by 1–3 ppbv/sunlit hour. In March 1996 the monthly mean SLIMCAT ozone is 50% greater than observations at 430–540 K. In both winters, ozone destruction rates peaked more rapidly and declined more slowly in the Match observations than in the SLIMCAT simulations. The differences between the observed and modelled cumulative ozone losses demonstrate that the total ozone destruction by the end of the winter is sensitive to errors in the instantaneous ozone loss rates of 1–3 ppbv/sunlit hour.  相似文献   

4.
Factors influencing the18O content of stratospheric H2O are reviewed in order to provide a theoretical framework for the interpretation of measurements of this quantity, which are now becoming available. Depletions in18O of 5–10% in stratospheric H2O are expected based on the known correlation between that of D and18O in tropospheric H2O and observed measurements of large (typically 50%) depletions of D in stratospheric H2O. H2O formed in the stratosphere as a result of oxidation of CH4 can be expected to reflect primarily the18O content of stratospheric O2, which is the same as that of tropospheric O2 (slightly enhanced with respect to standard mean ocean water). Thus, a reduction in the18O depletion is expected with increasing altitude, but not a large enhancement in18O in upper stratospheric H2O as found in recent far infrared measurements. The observed large enhancement of18O in stratospheric O3 is not expected to be reflected in stratospheric H2O. Necessary laboratory data for the improved quantification of these effects are reviewed.  相似文献   

5.
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   

6.
In July 1974 an NO/O3 chemiluminescent instrument was used to obtain measurements of NO in the stratosphere during two balloon flights launched from Churchill (59°N, 95°W). On the first flight, an altitude profile was obtained in which the NO volume mixing ratio was observed to increase from 0.3 to 2.7 ppbv between 19 and 29.5 km. On the second flight, the mixing ratio was observed to increase from 0.25 to 2.7 ppbv between 19 and 29 km and to remain almost constant at about 2.7 ppbv from 29 to 34.5 km. On this flight, the sunset decay of NO was also obtained while the payload was at a constant float altitude of 34.5 km. These decay measurements are compared satisfactorily with the results obtained from a time dependent stratospheric model.  相似文献   

7.
We have studied long-term changes in tropospheric NO2 over South India using ground-based observations, and GOME and OMI satellite data. We have found that unlike urban regions, the region between Eastern and Western Ghat mountain ranges experiences statistically significant decreasing trend. There are few ground-based observatories to verify satellite based trends for rural regions. However, using a past study and recent measurements we show a statistically significant decrease in NOX and O3 mixing ratio over a rural location (Gadanki; 13.48° N, 79.18° E) in South India. In the ground-based records of surface NOX, the concentration during 2010–11 is found to be lower by 0.9 ppbv which is nearly 60 % of the values observed during 1994–95. Small but statistically significant decrease in noon-time peak ozone concentration is also observed. Noon-time peak ozone concentration has decreased from 34?±?13 ppbv during 1993–96 to 30?±?15 ppbv during 2010–11. NOX mixing ratios are very low over Gadanki. In spite of low NOX values (0.5 to 2 ppbv during 2010–11), ozone mixing ratios are not significantly low compared to many cities with high NOX. The monthly mean ozone mixing ratio varies from 9 ppbv to 37 ppbv with high values during Spring and low values during late Summer. Using a box-model, we show that presence of VOCs is also very important in addition to NOX in determining ozone levels in rural environment and to explain its seasonal cycle.  相似文献   

8.
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   

9.
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   

10.
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   

11.
《大气与海洋》2013,51(4):283-299
Abstract

The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) series of high‐altitude balloon flights is being undertaken to investigate changes in the concentrations of northern hemisphere mid‐latitude stratospheric ozone, and of nitrogen and chlorine compounds that play a role in ozone chemistry. Four campaigns have been carried out to date, all from Vanscoy, Saskatchewan, Canada (52°01'N, 107°02'W, 511.0 m). The first MANTRA mission took place in August 1998, with the balloon flight on 24 August 1998 being the first Canadian launch of a large high‐altitude balloon in about fifteen years. The balloon carried a payload of instruments to measure atmospheric composition, and made measurements from a float altitude of 32–38 km for one day. Three of these instruments had been flown on the Stratoprobe flights of the Atmospheric Environment Service (now the Meteorological Service of Canada) in the 1970s and early 1980s, providing a link to historical data predating the onset of mid‐latitude ozone loss.

The primary measurements obtained from the balloon‐borne instruments were vertical profiles of ozone, NO2, HNO3, HCl, CFC‐11, CFC‐12, N2O, CH4, temperature, and aerosol backscatter. Total column measurements of ozone, NO2, SO2, and aerosol optical depth were made by three ground‐based spectrometers deployed during the campaign. Regular ozonesonde and radiosonde launches were also conducted during the two weeks prior to the main launch in order to characterize the local atmospheric conditions (winds, pressure, temperature, humidity) in the vicinity of the primary balloon flight. The data have been compared with the Model for Evaluating oZONe Trends (MEZON) chemical transport model, the University of California at Irvine photochemical box model, and the Canadian Middle Atmosphere Model (CMAM) to test our current understanding of model photochemistry and mid‐latitude species correlations. This paper provides an overview of the MANTRA 1998 mission, and serves as an introduction to the accompanying papers in this issue of Atmosphere‐Ocean that describe specific aspects and results of this campaign.  相似文献   

12.
Abstract

A coupled 1‐D radiative‐convective and photochemical diffusion model is used to study the influence of ozone photochemistry on changes in the vertical temperature structure and surface climate resulting from the doubling of atmospheric CO2, N2O, CH4 and increased stratospheric aerosols owing to the El Chichón volcanic eruption. It is found when CO2 alone is doubled, that the total ozone column increases by nearly 6% and the resulting increase in the solar heating contributes a smaller temperature decrease in the stratosphere (up to 4 K near the stratopause level). When the concentration of CO2, N2O and CH4 are simultaneously doubled, the total ozone column amount increases by only 2.5% resulting in a reduced temperature recovery in the stratosphere. Additional results concerning the effect of the interaction of ozone photochemistry with the stratospheric aerosol cloud produced by the El Chichón eruption show that it leads to a reduction in stratospheric ozone, which in turn has the effect of increasing the cooling at the surface and above the cloud centre while causing a slight warming below in the lower stratosphere.  相似文献   

13.
利用中尺度大气化学模式WRF/Chem对2013年3月6日华南地区一次平流层入侵事件及其对对流层低层臭氧的影响进行模拟研究。通过加入UBC（Upper Boundary Condition）上边界处理方案,弥补WRF/Chem模式未考虑平流层臭氧化学反应的不足。结合臭氧探空廓线资料、地面O3、CO、NOx、相对湿度、温度和风速等观测资料以及再分析资料对模拟结果进行定量评估,结果表明模式能较为真实地模拟本次平流层入侵过程。模拟分析进一步揭示:（1）副热带高空急流是本次平流层入侵的主要原因。当华南地区处在副热带急流入口区左侧下沉区域时,平流层入侵将富含臭氧的干燥空气输送到对流层中低层。（2）本次平流层入侵对对流层低层臭氧收支有重要影响,导致香港地区近地层臭氧体积混合比浓度明显上升,如塔门站夜间臭氧浓度升高21.3 ppb（1 ppb=1×10-9）。地面气象场和化学物种的分析进一步确认了平流层入侵的贡献。（3）采用动力学对流层顶高度时零维箱式模型和Wei公式计算得到的平流层入侵通量相当,分别为-1.42×10-3 kg m-2 s-1和-1.59×10-3 kg m-2 s-1,这一结果与前人研究相吻合,且与采用热力学对流层顶高度计算所得到的结果具有可比性。  相似文献   

14.
Effects of tropical deforestation on global and regional atmospheric chemistry   总被引：10，自引：0，他引：10  
A major portion of tropospheric photochemistry occurs in the tropics. Deforestation, colonization, and development of tropical rain forest areas could provoke significant changes in emissions of radiatively and photochemically active trace gases. A brief review of studies on trace-gas emissions in pristine and disturbed tropical habitats is followed by an effort to model regional tropospheric chemistry under undisturbed and polluted conditions. Model results suggest that changing emissions could stimulate photochemistry leading to enhanced ozone production and greater mineral acidity in rainfall in colonized agricultural regions. Model results agree with measurements made during the NASA ABLE missions. Under agricultural/pastoral development scenarios, tropical rain forest regions could export greater levels of N2O, CH4, CO, and photochemical precursors of NO y and O3 to the global atmosphere with implications for climatic warming.  相似文献   

15.
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   

16.
Continuous measurements of surface ozone (O3), NOx (NO + NO2) and meteorological parameters have been made in Kannur (11.9?°N, 75.4?°E, 5?m asl), India from November 2009 to October 2010. It was observed that O3 and NOx showed distinct diurnal and seasonal variabilities at this site. The annual average diurnal profile of O3 showed a peak of (30.3?±?10.4) ppbv in the late afternoon and a minimum of (3.2?±?0.7) ppbv in the early morning. The maximum value of O3 mixing ratio was observed in winter (44?±?3.1) ppbv and minimum during monsoon (18.46?±?3.5) ppbv. The rate of production of O3 was found to be higher in December (10.1?ppbv/h) and lower in July (1.8?ppbv/h) during the time interval 0800?C1000?h. A correlation coefficient of 0.52 for the relationship between O3 and [NO2]/[NO] reveals the role of NO2 photolysis that generates O3 at this site. The correlation between O3 and meteorological parameters indicate the influence of seasonal changes on O3 production. Investigations were further extended to explore the week day weekend variations in O3 mixing ratio at an urban site reveals the enhancement of O3. The variations of O3 mixing ratio with seasonal air mass flows were elucidated with the aid of backward air trajectories. This study also indicates how vapor phase organic species present in the ambient air at this location may influence the complex chemistry involving (VOCs) that enhances the production of O3 at this location.  相似文献   

17.
The paper discusses the potential effects on the ozone layer of gases released by the engines of proposed high altitude supersonic aircraft. The major problem arises from the emissions of nitrogen oxides which have the potential to destroy significant quantities of ozone in the stratosphere. The magnitude of the perturbation is highly dependent on the cruise altitude of the aircraft. Furthermore, the depletion of ozone is substantially reduced when heterogeneous conversion of nitrogen oxides into nitric acid on sulfate aerosol particles is taken into account in the calculation. The sensitivity of the aerosol load on stratospheric ozone is investigated. First, the model indicates that the aerosol load induced by the SO2 released by aircraft is increased by about 10–20% above the background aerosols at mid-high latitude of the Northern Hemisphere at 15 km for the NASA emission scenario A (the NASA emission scenarios are explained in Tables I to III). This increase in aerosol has small effects on stratospheric ozone. Second, when the aerosol load is increased following a volcanic eruption similar to the eruption of El Chichon (Mexico, April 1982), the ozone column in spring increases by as much as 9% in response to the injection of NO x from the aircraft with the NASA emission scenario A. Finally, the modeled suggests that significant ozone depletion could result from the formation of additional polar stratospheric clouds produced by the injection of H2O and HNO3 by the aircraft engines.  相似文献   

18.
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19.
Tropospheric distributions of ozone (O3) and water vapor (H2O) have been presented based on the Measurements of OZone and water vapor by Airbus In-Service AirCraft (MOZAIC) data over the metro and capital city of Delhi, India during 1996–2001. The vertical mixing ratios of both O3 and H2O show strong seasonal variations. The mixing ratios of O3 were often below 40 ppbv near the surface and higher values were observed in the free troposphere during the seasons of winter and spring. In the free troposphere, the high mixing ratio of O3 during the seasons of winter and spring are mainly due to the long-range transport of O3 and its precursors associated with the westerly-northwesterly circulation. In the lower and middle troposphere, the low mixing ratios of ∼20–30 ppbv observed during the months of July–September are mainly due to prevailing summer monsoon circulation over Indian subcontinent. The summer monsoon circulation, southwest (SW) wind flow, transports the O3-poor marine air from the Arabian Sea and Indian Ocean. The monthly averages of rainfall and mixing ratio of H2O show opposite seasonal cycles to that of O3 mixing ratio in the lower and middle troposphere. The change in the transport pattern also causes substantial seasonal variation in the mixing ratio of H2O of 3–27 g/kg in the lower troposphere over Delhi. Except for some small-scale anomalies, the similar annual patterns in the mixing ratios of O3 and H2O are repeated during the different years of 1996–2001. The case studies based on the profiles of O3, relative humidity (RH) and temperature show distinct features of vertical distribution over Delhi. The impacts of long range transport of air mass from Africa, the Middle East, Indian Ocean and intrusions of stratospheric O3 have also been demonstrated using the back trajectory model and remote sensing data for biomass burning and forest fire activities.  相似文献   

20.
中国部分清洁地区大气中N2O的浓度   总被引：11，自引：0，他引：11  
１９９３年４月—１９９５年８月对中国部分清洁地区大气的Ｎ２Ｏ浓度进行了现场观测，结果表明：农田（玉米田和麦田）大气的Ｎ２Ｏ平均浓度高达３２２．１－３４３．４ｐｐｂｖ，这是土壤排放Ｎ２Ｏ的结果；临安、龙风山和瓦里关山大气本底观测站（ＷＭＯ／ＧＡＷ）Ｎ２Ｏ的平均浓度分别为３１８．８±８．４ｐｐｂｖ，３１７．４±４．７ｐｐｂｖ和３１４．０±４．２ｐｐｂｖ。在此基础上，分析了大气Ｎ２Ｏ的分布及变化特征。另外，还对现场取样及Ｎ２Ｏ浓度测量技术作了初步分析和评价  相似文献   

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