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1.
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   

2.
The photooxidation of -humulene in the presence of NOx, natural sunlight, and rural background air was investigated using a combination of gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). Identification and quantification of gas and particulate reaction products were reported over the course of the reaction. The daytime photooxidation was carried out in a large outdoor smog chamber (190 m3). A wide range of ring retaining and ring opening products in the gas and particle phase are reported. On average, measured gas and particle phase products accounted for 44% of the reacted -humulene carbon. Measurements show that a number of reaction products with low vapor pressures (e.g. 3-seco--humulone aldehyde, 7-seco--humulone aldehyde, -humulal aldehyde, -humulene 3-oxide or -humulene 7-oxide, -humulaic/alic acid isomers, and 3-seco--14-hydroxyhumulone aldehyde) were found in the early stage of the reaction and may play an important role in the early formation of secondary organic aerosol. A detailed mechanism is proposed to account for most products observed in this investigation.  相似文献   

3.
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   

4.
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   

5.
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   

6.
Weekly bulk aerosol samples collected at Funafuti, Tuvalu (8°30S, 179°12E), American Samoa (14°15S, 170°35W), and Rarotonga (21°15S, 159°45W), from 1983 through most of 1987 have been analyzed for nitrate and other constituents. The mean nitrate concentration is about 0.11 g m–3 at each of these stations: 0.107±0.011 g m–3 at Funafuti; 0.116±0.008 at American Samoa; and 0.117±0.010 at Rarotonga. Previous measurements of mineral aerosol and trace metal concentrations at American Samoa are among the lowest ever recorded for the near-surface troposphere and indicate that this region is minimally affected by transport of soil material and pollutants from the continents. Consequently, the nitrate concentration of 0.11 g m–3 can be regarded as the natural level for the remote marine boundary layer of the tropical South Pacific Ocean. In contrast, over the tropical North Pacific which is significantly impacted by the transport of material from Asia and North America, the mean nitrate concentrations are about three times higher, 0.29 and 0.36 g m–3 at Midway and Oahu, respectively. The major sources of the nitrate over the tropical South Pacific are still very uncertain. A very significant correlation between the nitrate concentrations at American Samoa and the concentrations of 210Pb suggests that transport from continental sources might be important. This continental source could be lightning, which occurs most frequently over the tropical continents. A near-zero correlation with 7Be indicates that the stratosphere and upper troposphere are probably not the major sources. A significant biogenic source would be consistent with the higher mean nitrate concentrations, 0.16 to 0.17 g m–3, found over the equatorial Pacific at Fanning Island (3°55N, 159°20W) and Nauru (0°32S, 166°57E). The lack of correlation between nitrate and nss sulfate at American Samoa does not necessarily preclude an important role for marine biogenic sources.  相似文献   

7.
The probability of setting global temperature records is reconsidered in light of cooling due to the Mt. Pinatubo eruption. The cooling resets temperature by moving it away from the top of its 100-year range. Depending on the statistical model for temperature, this reset can lead to a much lower probability for a record in the next few years. The exercise illustrates how record setting depends on the underlying model, the current record value, and - if there is serial correlation- the current temperature.  相似文献   

8.
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   

9.
Diurnal and vertical ambient air measurements of the monoterpenes have been made in and above a Scots pine (Pinus sylvestris) forest of central Sweden, within the boreal northern coniferous biome. Sampling was done with Tenax TA, and analysis by GC and ion trap detection. Daytime mixing ratios were on the order of tenths of a ppbv from the forest floor to the top of the forest, and a factor of 2 or 3 lower above the forest. Mixing ratios at night were at the ppbv level, highest near the forest floor and the crown, and decreased with height above the forest. The highest total concentration observed was 8 ppbv inside the forest at 3 am (GMT). The average terpene composition was 3-carene 32%, -pinene 29%, limonene 18%, -pinene 10%, -phellandrene 7%, camphene 5%, and sabinene at less than 2%. The 3-carene/-pinene ratio varied with wind direction and speed, relative humidity, and wet/dry vegetation, but not with ozone or NO2 concentration, solar radiation, or temperature. Variations in the observed terpene composition at the sampling site are mainly caused by the influence of other vegetation in the vicinity of the site. It would seem that wet Scots pine emits more 3-carene relative to -pinene than does dry pine.  相似文献   

10.
Horizontal u and vertical w velocity fluctuations have been measured together with temperature fluctuations in the atmospheric surface layer, at a small height above a wheat crop canopy. Marginal probability density functions are presented for both individual fluctuations u, w, and for the instantaneous Reynolds stress uw, and heat fluxes w and u. Probability density functions of the velocity fluctuations deviate less significantly from the Gaussian form than the probability density of temperature. There appears to be closer similarity between statistics of the instantaneous heat fluxes than between the momentum flux and either of the heat fluxes investigated. The mean momentum flux receives equal contributions from the events referred to as ejections and sweeps in laboratory boundary layers. Sweeps provide the largest contribution to the heat fluxes.  相似文献   

11.
Summary The electromagnetic radiation of cloud discharge known as atmospheric radio noise field strength (ARNFS) shows a gradual fall from a frequency of 9 kHz to 81 kHz as studied over a period of two years at Calcutta, very close to Bay of Bengal. The main characteristic features of ARNFS at Calcutta are that-(i) ARNFS shows that midday median value is smaller than midnight median value in all months, (ii) level of daily minimum is higher in February and monsoon compared to other seasons, (iii) sunrise effect and sunset effect are well correlated with local sunrise and sunset times, (iv) the magnitude of sunrise fade and sunrise fade rate are maximum in April and lowest during winter period, (v) the magnitude of sunset fade is higher in premonsoon and postmonsoon while it is lowest in monsoon, (vi) number of occurrence of both sunrise effect and sunset effect is remark-ably smaller in monsoon. The positions of the sun and of atmospheric sources are jointly the causes of seasonal and diurnal variations. The missing of sunrise effect and sunset effect are due to local cloud activity and variation of electron density during geomagnetic storms.With 7 Figures  相似文献   

12.
Experimental evidence indicates that the diurnal behaviour of the fluxes of heat into the ground and into the atmosphere versus the net flux of radiation can be modelled by closed curves, the hourly values folowing one another in either a clockwise or counter clockfashion. A general formulation to express the different heat fluxes as a function of net radiation is proposed. This relationship between the different heat fluxes and can be expressed as a sum of three terms: the first indicates a direct proportionality to , the second gives the deviation from linearity and depends on /t, and the third gives the value of the flux when = 0. The formulae are then expressed as a function of time and the ratios between the heat fluxes and are evaluated. A comparison with the approximations generally used shows that the latter may be considered as particular cases of the more general equations proposed here.  相似文献   

13.
In the last decade, numerous studies of monoterpene hydrocarbons in the presence of ozone and oxides of nitrogen have been completed. Although insights about the reactivity of terpenes have been gained, and several products have been identified in the gas and aerosol phases, carbon balances have been generally poor. This paper describes a radiotracer technique which accounts for carbon-containing compounds in a smog chamber at the conclusion of a photooxidation or ozonolysis reaction. Instead of attempting to identify individual products, gas-phase compounds were separated from aerosols, and each phase was analyzed by a liquid scintillation counter. A carbon balance of 79 to 97% was obtained with 14C--pinene and ozone using this technique. The significance of the results are discussed in terms of the 14C--pinene concentrations used in this study, which were lower than concentrations used previously by one to four orders of magnitude. In spite of the lower concentrations, the gaseous and aerosol fractions observed in the present investigation are comparable to those observed by others. Possible reaction products are discussed with respect to likely mechanisms for -pinene oxidation.  相似文献   

14.
The yields of products have been calculated for the reactions of hydroxyl radicals and ozone with 19 of the two-through-six carbon anthropogenic alkenes. Based on their rate of reaction, mechanisms of reactions and the ambient air distribution for these alkenes their seasonal ambient air yields have been estimated.Aldehydes predominate as products irrespective of season, with smaller yields of several ketones. Other minor products include carboxylic acids, carbon monoxide, carbon dioxide, and alkenes. About a two-fold increase is estimated in the yields of hot biradicals and their products from summer to winter.One sensitivity analysis was made by recomputing yields at a different OH radical to O3 concentration than assumed most likely in the calculations discussed above. In addition, the sensitivity of product yields to an estimated range of seasonally averaged sunset-to-sunrise NO3 radical concentrations was calculated. The effects of free radical reactions are discussed, but these are believed to make a relatively minor contribution within the NO x -rich atmospheres that contain anthropogenic alkenes.The uncertainties in product yields associated with the range of NO3 radical concentrations assumed present is relatively small for aldehydes, as is the decrease in yield of the one carbon hot biradical. Larger uncertainties occur for ketones. Significant decreases in yields occur for larger hot biradicals, especially the branched-chain hot radicals in the presence of NO3 radicals.  相似文献   

15.
The variations of and in the drainage flow in the Brush Creek valley of western Colorado are investigated using data from Doppler acoustic sodars and instrumented towers. The data were obtained on two experimental nights during the 1984 ASCOT field study. There is good agreement between the variations derived from low-level observations of the sodars and those derived from the towers located throughout the valley. The observed hourly average and in the nocturnal drainage flow are about 20 ° to 25 ° and 5 °, respectively; these values are much larger than those generally observed over flat terrain during nighttime stable conditions. After sunrise (about 0600 MST), as the valley warms and the flow direction changes to up-valley, these parameters increase sharply to their peak values at about 0800 MST and then decrease to their normal daytime values after about two hours.In the drainage flow, the hourly average varies inversely with wind speed according to the relation u 0.7ms-1. The vertical standard deviation is much less enhanced by complex terrain than the horizontal standard deviation. The observed values are predicted fairly well by the local similarity theory.Oak Ridge Associated Universities (ORAU) Summer Research Participant at ATDD in 1987 andOak Ridge Associated Universities (ORAU) Summer Research Participant at ATDD in 1987 and  相似文献   

16.
Parameterization of evaporation from a non-plant-covered surface is very important in the hierarchy strategy of modelling land surface processes. One of the representations frequently used in its computation is the resistance formulation. The performance of the evaporation schemes using the , , and their combination resistance approaches to parameterize evaporation from bare soil surfaces is discussed. For that purpose, the nine schemes, based on a different dependence of and on volumetric soil moisture content and its saturated value, are used.The tests of performances of the considered schemes are based on time integrations by the land surface module (BARESOIL) using observed data. The 23 data sets at a bare surface experimental site in Rimski anevi, Yugoslavia on chernozem soil, were used for the resistance algorithm evaluation. The quality of the schemes was compared with the observed values of the latent heat flux using several statistical parameters.  相似文献   

17.
Among well-mixed multi-dimensional Lagrangian stochastic (LS) dispersion models, we observe that those in poorest agreement with observations produce spiralling trajectories, with an associated reduction in dispersion. We therefore investigate statistics of increments d ' to the orientation '= arctan(W'/U') of the Lagrangian velocity-fluctuation vector – as a possible means to distinguish the better LS models within the well-mixed class. Zero-spin models, having d' = 0, are found to provide best agreement with observations. It is not clear however, whether imposition of the zero-spin property selects (in conjunction with the well-mixed condition) a unique model.  相似文献   

18.
Turbulence measurements performed in a stable boundary layer over the sloping ice surface of the Vatnajökull in Iceland are described. The boundary layer, in which katabatic forces are stronger than the large-scale forces, has a structure that closely resembles that of a stable boundary layer overlying a flat land surface, although there are some important differences. In order to compare the two situations the set-up of the instruments on an ice cap in Iceland was reproduced on a flat grass surface at Cabauw, the Netherlands. Wind speed and temperature gradients were calculated and combined with flux measurements made with a sonic anemometer in order to obtain the local stability functions m and h as a function of the local stability parameter z/L. Unlike the situation at Cabauw, where m was linear as a function of z/L, in the katabatically forced boundary layer, the dependence of m on stability was found to be non-linear and related to the height of the wind maximum. Thermal stratification and the depth of the stable boundary layer however seem to be rather similar under these two different forcing conditions.Furthermore, measurements on the ice were used to construct the energy balance. These showed good agreement between observed melt and components contributing to the energy balance: net radiation (supplying 55% of the energy), sensible heat flux (30%) and latent heat flux (15%).Local sources and sinks in the turbulent kinetic energy budget are summed and indicate a reasonable balance in near-neutral conditions but not in more stable situations. The standard deviation of the velocity fluctuations u, v, and w, can be scaled satisfactorily with the local friction velocity u* and the standard deviation of the temperature fluctuation with the local temperature scale *.  相似文献   

19.
This is one of a series of papers on the Askervein Hill Project. It presents results on the variations in mean wind speed at fixed heights (z) above the ground from linear arrays of anemometer posts and towers. Most of the data are for z = 10 m but some are for z = 3 m. Selected and directionally grouped data from the 55 Mean Flow runs are presented together with mean flow data from Askervein '83 Turbulence runs. Comparisons are made between the data and guideline estimates of fractional speed-up ratio at hilltop locations and between the data and MS3DJH/3 model predictions along the tower lines. There is good agreement in most cases.  相似文献   

20.
A mass-flux approach is applied to observational data obtained in a convective boundary layer topped with stratocumulus clouds. The observational data were obtained from aircraft measurements during the Atlantic Stratocumulus Transition Experiment (ASTEX). A conditional sampling method is used to calculate average updraft and downdraft values. The vertical fluxes calculated with the mass-flux approach are found to be proportional to the real (measured) fluxes, with a proportionality factor being about 0.6. This value is predicted by theory for two variables having a joint Gaussian distribution function; proportionality factor = 2-1 0.637. The horizontal fractional entrainment and detrainment rates calculated from the data ( 1–2 × 10-2 m-1) are an order of magnitude higher than the rates obtained by large eddy simulations for cumulus convection ( 2–3 × 10-3 m-1) and two orders of magnitude higher than those used in modelling cumulus convection with a mass-flux scheme in an operational weather forecast model ( 3 × 10-4 m-1). A numerical mass-flux model for the thermodynamics was developed and showed that results are in good agreement when compared with measured profiles of the liquid water content.  相似文献   

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