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1.
Atmospheric oxidation of monoterpenes contributes to formation of tropospheric ozone and secondary organic aerosol, but their products are poorly characterized. In this work, we report a series of outdoor smog chamber experiments to investigate both gaseous and particulate products in the ozone oxidation of four monoterpenes: -pinene, -pinene, 3-carene, and sabinene. More than ten oxygenated products are detected and identified in each monoterpene/O3 reaction by coupling derivatization techniques and GC/MS detection. A denuder/filter pack sampling system is used to separate and simultaneously collect gas and aerosol samples. The identified products, consisting of compounds containing carbonyl, hydroxyl, and carboxyl functional groups, are estimated to account for about 34–50%, 57%, 29–67%, and 24% of the reacted carbon mass for -pinene, sabinene, -pinene, and 3-carene, respectively. The identified individual products account for >83%, 100%, >90%, and 61% of the aerosol mass produced in the ozone reaction of -pinene, sabinene, -pinene, and 3-carene. The uncertainty in the yield data is estimated to be ±50%. Many of the products partition between gas and aerosol phases, and their gas-aerosol partitioning coefficients are determined and reported here. Reaction schemes are suggested to account for the products observed.  相似文献   

2.
Formation of Organic Aerosols from the Oxidation of Biogenic Hydrocarbons   总被引：15，自引：0，他引：15  
Measurements of aerosol formation during thephotooxidation of -pinene, -pinene,d-3-carene, d-limonene, ocimene, linalool, terpinene-4-ol, andtrans-caryophyllene were conducted in anoutdoor smog chamber. Daylight experiments in thepresence of and dark experiments withelevated ozone concentrations were performed. Theevolution of the aerosol was simulated by theapplication of a gas/particle absorption model inconnection with a chemical reaction mechanism. Thefractional aerosol yield is shown to be a function ofthe organic aerosol mass concentration andtemperature. Ozone and, for selected hydrocarbons, theNO3 reaction of the compounds were found torepresent efficient routes to the formation ofcondensable products. For initial hydrocarbon mixingratios of about 100 ppb, the fractional aerosol yieldsfrom daylight runs have been estimated to be 5%for open-chain hydrocarbons, such as ocimene andlinalool, 5–25% for monounsaturated cyclicmonoterpenes, such as -pinene, d-3-carene, orterpinene-4-ol, and 40% for a cyclic monoterpenewith two double bonds like d-limonene. For the onlysesquiterpene investigated, trans-caryophyllene, afractional aerosol yield of close to 100% wasobserved. The majority of the compounds studied showedan even higher aerosol yield during dark experimentsin the presence of ozone.  相似文献   

3.
This paper shows a comparative study of particle and surface ozone concentration measurements undertaken simultaneously at two distinct semi-urban locations distant by 4 km at Saint-Denis, the main city of La Réunion island (21.5° S, 55.5° E) during austral autumn (May 2000). Black carbon (BC) particles measured at La Réunion University, the first site situated in the suburbs of Saint-Denis, show straight-forward anti-correlation with ozone, especially during pollution peaks ( 650 ng/m3 and 15 ppbv, for BC and ozone respectively) and at night-time (90 ng/m3 and 18.5 ppbv, for BC and ozone respectively). NOx (NO and NO2) and PM10 particles were also measured in parallel with ozone at Lislet Geoffroy college, a second site situated closer to the city centre. NOx and PM10 particles are anti-correlated with ozone, with noticeable ozone destruction during peak hours (mean 6 and 9 ppbv at 7 a.m. and 8 p.m. respectively) when NOx and PM10 concentrations exhibit maximum values. We observe a net daytime ozone creation (19 ppbv, O3 +4.5 ppbv), following both photochemical and dynamical processes. At night-time however, ozone recovers (mean 11 ppbv) when anthropogenic activities are lower ([BC] 100 ng/m3). BC and PM10 concentration variation obtained during an experiment at the second site shows that the main origin of particles is anthropogenic emission (vehicles), which in turn influences directly ozone variability. Saint-Denis BC and ozone concentrations are also compared to measurements obtained during early autumn (March 2000) at Sainte-Rose (third site), a quite remote oceanic location. Contrarily to Saint-Denis observations, a net daytime ozone loss (14.5 ppbv at 4 p.m.) is noticed at Sainte-Rose while ozone recovers (17 ppbv) at night-time, with however a lower amplitude than at Saint-Denis. Preliminary results presented here are handful data sets for modelling and which may contribute to a better comprehension of ozone variability in relatively polluted areas.  相似文献   

4.
Six locations across mainland Portugal were selected for exposing Parmelia sulcata, for a one-year period (8 months for one site), with simultaneous measurement of total (dry + wet) deposition (one-month periods). The exposed lichens and the total (dry + wet) deposition were analysed for cobalt contents by INAA (instrumental neutron activation analysis) and ICP-MS (inductively coupled plasma mass spectroscopy), respectively. The designated wet deposition was evaluated through the collected water volume; the designated dry deposition was assessed after the (dried) residual mass of the wet deposition. An excellent agreement between Co contents in exposed lichens and the cumulative (1) Co contents in the dry deposition, (2) dry deposition, and (3) wet deposition has been found for the locations with alternate drought and precipitation months, high dry deposition, and high Co contents in the latter. Continuous rainfall was found to hinder the Co accumulation in the lichen due to its release from the lichen and/or lower Co contents in the dry deposition. At three locations, P. sulcata Co contents, after subtraction of the background (before exposure), equalled or exceeded the Co contents in the cumulative dry deposition at the end of the exposure time. The optimal exposure period for this species likely depends on the exposure conditions.  相似文献   

5.
Flux Footprints Within and Over Forest Canopies   总被引：8，自引：1，他引：7  
The characteristics of turbulence within a forest arespatially heterogeneous and distinct from thoseassociated with the surface boundary layer. Consequently, the size and probability distribution offlux footprints emanating from sources below aforest canopy have the potential to differ from thoseobserved above forests.A Lagrangian random walk model was used toinvestigate this problem since no analytical solutionof the diffusion equation exists. Model calculations suggest that spatialcharacteristics of flux footprint probabilitydistributions under forest canopies are muchcontracted, compared to those evaluated in the surfaceboundary layer. The key factors affecting thestatistical spread of the flux footprint, and theposition of the peak of its probability distribution,are horizontal wind velocity and the standarddeviations of vertical and horizontal velocityfluctuations. Consequently, canopies, which attenuatemean horizontal wind speed, or atmospheric conditions,which enhance vertical velocity fluctuations, willcontract flux footprint distributions mostly near thefloor of a forest. It was also found that theprobability distributions of the flux footprint arenarrower when horizontal wind velocity fluctuationsare considered, instead of the simpler case that considers only vertical velocity fluctuations and meanhorizontal wind velocity.  相似文献   

6.
Upto 13% of -pinene and 3-carene had reacted after 213 s in this dark experimental set-up, where O3, NO and NO2 were mixed with terpenes at different relative humidities (RHs). The different experiments were planned according to an experimental design, where O3, NO2, NO, RH and reaction time were varied between high and low settings (25 and 75 ppb, 15 and 42%, 44 and 213 s). An increased amount of -pinene and 3-carene reacted in the chamber was observed, when the level of O3, NO and reaction time was increased and RH was decreased. In the study, it was found that different interactions affected the amount of terpene reacted as well. These interactions were between O3 and NO, O3 and reaction time, NO and RH, and between NO and reaction time.  相似文献   

7.
The formation yields of nine carbonyl products are reported from the gas-phase OH radical-initiated reactions (in the presence of NO x ) and the O3 reactions with seven monoterpenes. The products were identified using GC/MS and GC-FTIR and quantified by GC-FID analyses of samples collected on Tenax solid adsorbent cartridges. The identities of products from camphene, limonene and -pinene were confirmed by comparison with authentic standards. Sufficient quantities of products from the 3-carene, limonene, -pinene, sabinene and terpinolene reactions were isolated to allow structural confirmation by proton NMR spectroscopy. The measured total carbonyl formation yields ranged from non-detectable for the OH radical reaction with camphene and the O3 reactions with 3-carene and limonene to 0.5 for the OH radical reaction with limonene and the O3 reaction with sabinene.  相似文献   

8.
We implemented the windbreak model of Wang and Takle to investigate whythose authors could have obtained better agreement with the Bradley andMulhearn wind reduction measurements in the far lee of a fence, than wasobtained by Wilson using a very similar model. According to our experiencethe improvement of the Wang-Takle simulations (relative to Wilson's)largely arises from their having used a too-shallow computational domain(8H, versus Wilson's 47H; H being the windbreak height).  相似文献   

9.
Summary Mechanisms associated with Alpine lee cyclogenesis during the early phase of their generation are investigated using a variational quasigeostrophic filter technique. It was possible to extract the quasigeostrophic signal from the available analyzed real data set.The results presented here are for the 11–12 March 1982, an example of so-called orographically induced lee cyclogenesis. Non-quasigeostrophic fields, calculated as a difference between observations and the quasigeostrophic fields, show significant magnitudes indicating the possible importance of non-quasigeostrophic processes. A dipole structure in the residual geopotential field was observed, similar to the results of numerical model experiments. Also, a strong upper-level non-quasigeostrophic divergence was found in the Alpine region 24 hours prior to lee cyclogenesis, lasting for 6–12 hours. On the other hand, quasigeostrophic results indicate only a local effect of mountain slopes, suggesting possibly a dominant role of the low-level blocking. A hypothetical scenario of Alpine lee cyclogenesis is proposed, based on results obtained here.With 14 Figures  相似文献   

10.
The paper considers a puff diffusion in its inertial stage when particle separation obeys the laws of the inertial subrange and depends only on eddy energy dissipation rate . The can be determined in the surface layer by the turbulent kinetic energy equation. Similarity equations connect with diffusion measure .A simple analytical model has been deduced to estimate pollutants diffusion during calms.  相似文献   

11.
A Comparative Analysis of Transpiration and Bare Soil Evaporation   总被引：4，自引：0，他引：4  
Transpiration Ev and bare soil evaporation Eb processes are comparatively analysed assuming homogeneous and inhomogeneous areal distributions of volumetric soil moisture content . For a homogeneous areal distribution of we use a deterministic model, while for inhomogeneous distributions a statistical-deterministic diagnostic surface energy balance model is applied. The areal variations of are simulated by Monte-Carlo runs assuming normal distributions of .The numerical experiments are performed for loam. In the experiments we used different parameterizations for vegetation and bare soil surface resistances and strong atmospheric forcing. According to the results theEv()-Eb() differences are great, especially in dry conditions. In spite of this, the available energy flux curves of vegetation Av() and bare soil Ab() surfaces differ much less than the Ev() and Eb() curves. The results suggest that Ev is much more non-linearly related to environmental conditions than Eb. Both Ev and Eb depend on the distribution of , the wetness regime and the parameterization used. With the parameterizations, Eb showed greater variations than Ev. These results are valid when there are no advective effects or mesoscale circulation patterns and the stratification is unstable.  相似文献   

12.
Summary The performance of evaporation schemes with and approach and their combination within resistance representation of evaporation from bare soil surface is discussed. For this purpose nine schemes, based on different functions of or , on the ratio of the volumetric soil moisture content and its saturated value are used.The quality of the chosen schemes has been evaluated using the results of time integration by the coupled soil moisture and surface temperature prediction model, BARESOIL, using in situ data. A sensitivity analysis was made using two sets of data derived from the volumetric soil moisture content of the top soil layer. One with values below the wilting point (0.17 m3m–3) and the second with values above 0.20m3m–3. Data sets were obtained at the experimental site Rimski anevi, Yugoslavia, from the bare surface of a chernozem soil.With 4 Figures  相似文献   

13.
E- turbulence model predictions of the neutralatmospheric boundary layer (NABL) are reinvestigated to determine thecause for turbulence overpredictions found in previous applications. Analytical solutions to the coupled E and equations for the case of steady balance between transport and dissipation terms, the dominant balance just below the NABL top, are derived. It is found that analytical turbulence profiles laminarizeat a finite height only for values of closure parameter ratio c 2 /e equal toor slightly greater than one, with laminarization as z for greater . The point = 2 is additionally foundthat where analytical turbulent length scale (l) profilesmade a transition from ones ofdecreasing ( < 2) to increasing ( > 2)values with height. Numerically predicted profiles near the NABL topare consistent with analytical findings. The height-increasingvalues of l predicted throughout the NABL with standard values ofclosure parameters thus appear a consequence of 2.5(> 2), implied by these values (c 2 = 1.92, = 1.3, e = 1). Comparison of numericalpredictions with DNS data shows that turbulence overpredictions obtained with standard-valued parameters are rectifiedby resetting and e to 1.1 and 1.6, respectively, giving, with c 2 = 1.92, 1.3, and laminarization of the NABL's cappingtransport-dissipation region at a finite height.  相似文献   

14.
Emissions of volatile organic compounds (VOCs) from sunflower (Helianthus annuus L. cv. giganteus) were measured in a continuously stirred tank reactor. The compounds predominantly emitted from sunflower were: isoprene, the monoterpenes -pinene, -pinene, sabinene, 3-carene and limonene, an oxygenated terpene, not positively identified so far and the sesquiterpene -caryophyllene. Emission rates ranged from 0.8 x 10–16 to 4.3 x 10 –15 mol cm–2 s–1 at a temperature of 25°C and at a light intensity of 820 µEm–2 s–1. A dependence of the emission rates on temperature as well as on light intensity was observed. The emission rates of -pinene, sabinene and thujene from beech (Fagus sylvatica L.) were also affected by temperature as well as by light intensity. Our results suggest that an emission algorithm for all compounds emitted from sunflower and beech has to consider temperature and light intensity simultaneously. The observations strongly indicate that the emissions of VOCs from sunflower and beech are in part closely coupled to the rate of biosynthesis and in part originate from diffusion out of pools. The emission rates can be described by an algorithm that combines the model given by Tingey and coworkers with the algorithm given by Guenther and coworkers after slight modification.  相似文献   

15.
The gas and particle phase reaction products of a mixture of the atmospherically important terpenes -pinene and -pinene with the atmospheric oxidants O3 and OH/NOx were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of a mixture of -pinene and -pinene in the presence of O3/air, and the daytime oxidation of a mixture of -pinene + -pinene with NOx air in the presence of natural sunlight were carried out in the University of North Carolina's large outdoor smog chamber (190 m3) located in Chatham County, North Carolina. Mass balances for gaseous and aerosol reaction products are reported over the course of the reaction. More than twenty-nine products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for 74 to 80% of the reacted -pinen/-pinene mixture carbon. Measurements show that a number of reaction products were found in both O3 and NOx system [pinonaldehyde, pinic acid, pinonic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxy-nopinone, 3-hydroxy-nopinone, and nopinone]. Pinonic acid, pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, and 10-hydroxypinonic acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols.  相似文献   

16.
Wintertime observations of mesoscale cellular convection (MCC) over the East China Sea have resulted in criteria that have a remarkable similarity to those reported by Woodcock (1975) in the study of thermals and gull flight behavior. It has been determined that the surface wind speed (V) and the air-sea temperature difference (T) prescribe unique and compatible conditons for both the occurrence of MCC and soaring by sea gulls. Specifically, the onset of MCC when V is between 5 and 9 m s–1 is inversely proportional to T in the range 5 to 7 °C. Elsewhere, the onset of MCC occurs under conditions of direct proportionality between V and T. Necessary conditions for the occurrence of MCC due to heating from below are T 5 °C and V 5 m s–1. The boundaries of the convective regime for MCC are discussed and interpreted in accordance with the regime for sea-gull soaring and similarity concepts.  相似文献   

17.
A dynamical model for the late-Quaternary global variations of 18O, mean ocean surface tempeature , ice mass I, deep ocean temperature , and atmospheric carbon dioxide concentration , is constructed. This model consists of two diagnostic equations (for 18O and ), and three prognostic equations (for I, , and ) of a form studied extensively in previous articles. The carbon dioxide equation includes forcing by a representation of the Milankovitch earth-orbital radiation effects, and contains a basic instability that drives a free oscillation of period near 100,000 years. The system is constrained to conserve mass and energy, contain physically plausible feedbacks including a system time constant no greater than 10.000 years, and be robust (i. e., structurally stable in the presence of expected noise levels and uncertainties in values of coefficients). Within the limits of these constraints, coefficients are chosen such that (i) the solution gives a good fit to the observed SPECMAP 18O variations, and (ii) the ice mass variations are qualitatively similar to the 18O variations. The predicted long term variations of sea surface temperature and atmospheric carbon dioxide are in reasonably good agreement with the limited observational evidence available for these quantities, while the predicted variations of deep ocean temperature remain to be verified when paleoclimatic estimates of this quantity become available. The relative contributions of ice mass changes and surface water temperature changes to the variations of 18O at any time are given by the model.  相似文献   

18.
The standard E – model generates aplanetary boundary layerthat appears to be much too deep. The cause of theproblem is traced to the equation for the dissipationrate () of turbulent kinetic energy (E), specifically theparameterization of dissipation production anddestruction. In the context of atmosphericboundary-layer modelling, we argue that a part of thedissipation production should be modelled as the inputto the spectral cascade from the energy-containingpart of the spectrum, with a characteristic length , while the equilibrium imbalancebetween local production and destruction ofdissipation is modelled as proportional toE2/E, as in the standard model. Wepropose an E – – turbulence closurescheme, in which both the mixing length, m, and are prescribed. The importance ofthe equation is diminished, though itstill determines the dissipation rate in the Eequation.  相似文献   

19.
Components of the radiation and energy balances were measured over a clear-cut area and a mature, mixed forest during the summer of 1981 at the Petawawa National Forestry Institute, Chalk River, Ontario. The work concentrated on the clear-cut site which supported a canopy layer composed primarily of bracken fern and logging remnants.Forty days of radiation data were collected at the clear-cut site. After the first four weeks of measurements (the green season), most of the ferns quickly died, and their foliage changed appearance from a green to brownish colour (the brown season). The daily mean reflection coefficient of solar radiation determined over the green season was 0.20 and decreased to 0.13 for the brown season. The corresponding value for the forest was 0.13, based on a limited amount of data. The clear-cut site received 11% and 21% less net radiation than the forest on a 24-hr and daylight-hours basis, respectively, as a consequence of the higher reflection coefficient and larger daytime longwave radiation emission.A reversing temperature difference measurement system (RTDMS), incorporating ten-junction thermopiles was employed at each site in order to determine Bowen ratios () via differential psychrometry. Both systems performed well, especially the RTDMS over the forest which was capable of resolving very small differences of temperature, typically less than 0.2 °C over a height of 3 m. The mean hourly Bowen ratio, calculated from values from 0800 to 1600 hr, varied from 0.2 to 1.0 for the forest and from 0.4 to 0.8 for the clear-cut site in the green season.A significant canopy heat storage component of the energy balance, Q S , was found at the clear-cut site. In the early morning, a portion of the available energy was used to heat the biomass materials and air within the canopy layer. The stored heat within the canopy was released later in the day, increasing the available energy total.The daily mean value of the Priestley-Taylor coefficient (Priestley and Taylor, 1972) for the green season at the clear-cut site was 1.14, and individual values tended to increase during wet surface conditions and decrease when the surface dried. The daylight mean value during dry canopy conditions at the forest was 1.05, and much higher values occurred when the canopy was wet. The enhancement of for the wet forest was a result of the evaporation of intercepted rain (which is not limited by stomatal resistance) and the concomitant transfer of sensible heat to the forest.  相似文献   

20.
Summary A nonhydrostatic numerical simulation of a tropical cyclone is performed with explicit representation of cumulus on a meso- scale grid and for a brief period on a meso- scale grid. Individual cumulus plumes are represented by a combination of explicit resolution and a 1.5 level closure predicting turbulent kinetic energy (TKE).The results demonstrate a number of expected and unexpected important scale interaction processes. Within the central core of the developing cyclone, meso- convective regions grow and breakdown into propagating inertiagravity waves throughout the lifecycle of the cyclone. In the early stages, the amplitude of pressure fluctuations associated with the meso- scale convection exceed the central pressure of the cyclone and strongly modulate its intensity. With each meso- scale pulsation, the cyclone core increases in strength, measured by the central pressure deficit. The increasingly strong inertial frequency of the storm core acts to increasingly trap the convection induced heating within the core by balancing the tangential wind against the low central pressure, before the meso- scale convection breaks down and sends the warmth away as a propagating wave. Eventually, the slow manifold's amplitude exceeds the amplitude of the meso- scale oscillations and a stable eye region is formed. As inertial instability increases, increasingly high thermal warmth can be protected in the core, allowing persistent subsidence to form and to clear out the cyclone eye.On the outside of the eye wall, strong inertial stability gradients in the troposphere cause convective warming to split the inflow to the eye wal! and spawn outwardly propagating inertia gravity waves. These waves carry away all of the heating forced by convection that is not inertially trapped by the eye wall and act as a moderating influence on storm intensity.Inertia gravity waves are also spawned in the stratosphere at the top of the eye wall by the revolution of asymmetric cumulus structures. In all instances, the tropospheric waves are coupled to the propagating stratospheric waves which both move at 35 ms–1, although there are many instances where the stratospheric waves seem to have no tropospheric counterpart. Hence the anvil top forcing and low level breakdown are linked.The outwardly propagating inertia gravity waves act to initiate outer bands of convection. This initiation is with the assistance of low level boundary layer variations of density related to previous convection and to virga falling from the anvil which moistens and destabilizes the mid levels of e minimum. The convection initiated by these waves does not move substantially outward with the wave, although may appear to develop outward discontinuously.With 12 Figures  相似文献   

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