Simultaneous Measurements of Black Carbon, PM10, Ozone and NOx Variability at a Locally Polluted Island in the Southern Tropics

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). NO_x (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. NO_x 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 NO_x 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.     

A non-linear climate oscillator controlled by biogeochemical cycling in the ocean: an alternative model of Quaternary ice age cycles

A new, biogeochemical model of ice age cycles is developed and applied which explains major features of climate variations in the late Quaternary —rapid ice age terminations, large glacial-interglacial amplitudes and 100-kyr cycles — in a way consistent with the paleorecord. Existing models which invoke non-linear, ice-sheet-earth-crust dynamics to explain ice age cycles are not consistent with simultaneous terminations in both hemispheres and other phase relationships implied by the paleorecord. The present model relates climate change to oscillations of oceanic primary (new) production controlled by the availability of inorganic nitrogen. Large oscillations follow shelf erosion events triggered by small sea-level drops. These drops are due to glacial buildup associated with a minimum in Northern Hemisphere insolation. Rapid global warming at terminations is initiated by open ocean denitrification events leading to new production crashes and rapid modification of atmospheric trace gas concentrations (CO₂, DMS, N₂O). Other feedbacks of the land-ice-atmosphere-ocean system control the rest of the climate cycle. 100-kyr cycles derive from orbital pacemaking of the strong, low-frequency model response. Results suggest that the climate regime transition near 800 kyr B.P. may be related to changes in the continental shelf slope, that existing chronologies based on orbital tuning may need to be revised and that temporary increases in atmospheric N₂O concentrations at terminations, due to the denitrification events, may have caused significant greenhouse warming. A spike of elevated N₂O concentration at terminations may be recorded in polar ice.     

Gaseous and Particulate Oxidation Products Analysis of a Mixture of α-pinene + β-pinene/O3/Air in the Absence of Light and α-pinene + β-pinene/NOx/Air in the Presence of Natural Sunlight

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/NO_x 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 NO_x 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 NO_x 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.     

A study of the sensitivity of bare soil evaporation schemes to soil surface wetness,using the coupled soil moisture and surface temperature prediction model,BARESOIL

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     

Application of a “Big-Tree” model to regional climate modeling: a sensitivity study

Summary ¶In order to better understand land-atmosphere interactions and increase the predictability of climate models, it is important to investigate the role of forest representation in climate modeling. Corresponding to the big-leaf model commonly employed in land surface schemes to represent the effects of a forest, a so called big-tree model, which uses multi-layer vegetation to represent the vertical canopy heterogeneity, was introduced and incorporated into the National Center for Atmospheric Research (NCAR) regional climate model RegCM2, to make the vegetation model more physically based. Using this augmented RegCM2 and station data for China during 1991 Meiyu season, we performed 10 experiments to investigate the effects of the application of the big-tree model on the summer monsoon climate.With the big-tree model incorporated into the regional climate model, some climate characteristics, e.g. the 3-month-mean surface temperature, circulation, and precipitation, are significantly and systematically changed over the model domain, and the change of the characteristics differs depending on the area. Due to the better representation of the shading effect in the big-tree model, the temperature of the lower layer atmosphere above the plant canopy is increased, which further influences the 850hPa temperature. In addition, there are significant decreases in the mean latent heat fluxes (within 20–30W/m²) in the three areas of the model domain.The application of the big-tree model influences not only the simulated climate of the forested area, but also that of the whole model domain, and its impact is greater on the lower atmosphere than on the upper atmosphere. The simulated rainfall and surface temperature deviate from the originally simulated result and are (or seem to be) closer to the observations, which implies that an appropriate representation of the big-tree model may improve the simulation of the summer monsoon climate.We also find that the simulated climate is sensitive to some big-tree parameter values and schemes, such as the shape, height, zero-plane displacement height and mixing-length scheme. The simulated local/grid differences may be very large although the simulated areal-average differences may be much lower. The area-average differences in the monthly-mean surface temperature and heat fluxes can amount to 0.5°C and 4W/m², respectively, which correspond to maximum local/grid differences of 3.0°C and 40W/m² respectively. It seems that the simulated climate is most sensitive to the parameter of the zero-plane displacement among the parameters studied.     

Arctic hazes in summer over Greenland and the North American Arctic: II. Nature and concentrations of accumulation-mode and giant particles

Airborne measurements made during August 1985 over Greenland and its environs show that both accumulation-mode (0.1 m D2.0 m) and giant (D2 m) particles were present in relatively high concentrations in arctic haze layers and that the accumulation-mode particles dominated light scattering. Particles with diameters (D) between 1 and 4 m consisted predominately of mixed materials, small and dense inclusions, and probably organic compounds containing sulfur. Many of the particles from 0.1 to 1 m in diameter were also of mixed composition, with sulfuric acid, ammonium sulfate and organics probably the dominant constituents.     

Bioaccumulation of Cobalt in Parmelia sulcata

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.     

On Trajectory Curvature as a Selection Criterion for Valid Lagrangian Stochastic Dispersion Models

Recently Wilson and Flesch (Boundary-Layer Meteorology, 84, 411-426, 1997) suggested that the average increment d z to the orientation = arctan(w/u) of the Lagrangian velocity-fluctuation vector can be used to distinguish the better Lagrangian stochastic models within the well-mixed class. Here it is demonstrated that the specification of d z constitutes neither a sufficient or universally applicable criterion to distinguish the better Lagrangian stochastic models within the well-mixed class. The hypothesis made by Wilson and Flesch that Lagrangian stochastic models with /P_E irrotational are zero-spin models, having d z=0, is proven     

Analytical investigations of horizontal meso-scale momentum equations with Newtonian nudging

Summary This study presents an analytical investigation of the local behaviour of the solution to a mesoscale model with Newtonian nudging when observed winds are time varying. The analysis examines each Fourier component of the time series of observed winds. Unlike the case with a constant observed wind, the nudged wind vector does not asymptotically approach the observed wind. In response to sinusoidal oscillation of the observed wind, the nudged wind vector is always on a half circle connecting the vector ends of the observed and un-nudged modelled winds. When nudging parameter 0, the nudged wind vector approaches the un-nudged wind; when , the nudged wind vector approaches the observed wind. For commonly used values of nudging parameter , the modelled wind field always carries errors.A target nudging scheme is devised in this study in order to ensure the model result is identical to observed winds with sinusoidal oscillation. Investigation shows that such a target wind exists for a finite value of , and the magnitude of the target-nudging term is about the same as that of a normal nudging term if f, wheref is the Coriolis parameter and is the frequency of the wind oscillation.With 7 Figures     

Thermal comfort of man in different urban environments

Summary On July 29, 1985, a hot summer day, biometeorological measurements were performed simultaneously in three different urban structures within the city of Munich and in the trunk space of a nearby tall spruce forest. Based on the results of these experiments the following thermophysiologically relevant biometeorological indices were calculated: Predicted mean vote, skin wettedness and physiologically equivalent temperature. These three indices are derived from different models for the human energy balance. They allow the assessment of the thermal components of the microclimates at the selected sites with regard to application in urban planning. The results quantitatively show the great heat stress in the urban structure street canyon, exposed to south, whereas in the trunk space of the tall spruce forest there is nearly an optimal climate even on hot summer days. Between these extremes the results for street canyon, exposed to north show a little higher heat load than for backyard with trees.

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Zusammenfassung An einem heißen Sommertag, dem 29. Juli 1985, wurden in drei Stadtstrukturen in München und im Stammraum eines nahegelegenen Fichtenhochwaldes zeitgleich biometeorologische Messungen durchgeführt. Mit den Meßergebnissen wurden folgende thermophysiologisch relevante biometeorologische Indizes berechnet: Predicted mean vote, Hautbenetzungsgrad und physiologisch äquivalente Temperatur. Diese drei Indizes beruhen auf verschiedenen Modellen zur menschlichen Energiebilanz. Mit den drei Indizes wurden die thermischen Komponenten der Mikroklimate an den ausgewählten Meßplätzen im Hinblick auf Stadtplanungsaufgaben bewertet. Die Ergebnisse zeigen quantitativ die relativ große Hitzebelastung bei der Stadtstruktur Straßenschlucht, nach Süd exponiert, während im Stammraum des Fichtenhochwaldes selbst an heißen Sommertagen nahezu optimale Bedingungen herrschen. Zwischen diesen Extremen liegen die Ergebnisse für die anderen Meßplätze, wobei für Straßenschlucht, nach Nord exponiert die Wärmebelastung etwas höher als für Innenhof mit Bäumen ist.

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With 6 Figures     

Experiments On Buoyant Plume Dispersion In A Laboratory Convection Tank

Plume dispersion in the convective boundary layer (CBL) is investigated experimentally in a laboratory convection tank. The focusis on highly-buoyant plumes that loft near or become trapped in the CBL capping inversion and resistdownward mixing. Such plumes are defined by dimensionless buoyancy fluxes F_* 0.1, where F_* = F_b/(U w_* ² z_i), F_b is the stack buoyancy flux,U is the mean wind speed, w_* is the convective velocity scale, and z_i is the CBL depth. The aim is to obtain statistically-reliable mean (C) and root-mean-square (rms, _c) concentration fields as a function of F_* and the dimensionless distance X = w_*x/(U z_i), where x is the distance downstream of the source.The experiments reveal the following mainresults: (1) For 3 X 4and F_* 0.1, the crosswind-integrated concentration (CWIC) fields exhibit distinctly uniform profiles below z_i with a CWIC maximum aloft, in contrast to the nonuniform profiles obtained earlier by Willis and Deardorff. (2) The lateral dispersion (_y) variation with X is consistent with Taylor's theory for _* 0.1 and a buoyancy-enhanced dispersion, _y/z_i F_* ^1/3X^2/3, forF_* = 0.2 and 0.4. (3) The entrapment, the plume fraction above z_i, has a mean (E) that follows a systematic variationwith X and F_*, and a variability (_e/E) that is broad ( 0.3 to 2) near the source but subsides to 0.25 far downstream. (4) Vertical profiles of the concentration fluctuation intensity (c/C) are uniform for z < z_i and X > 1.5, but exhibit significant increases: (a) at the surface and close to the source (X 1.5), and(b) in the entrainment zone. (5) The cumulative distribution functions (CDFs) of the scaled concentration fluctuations (c/_c) separate into mixed-layer and entrainment-layer CDFs for X 2, with the mixed-layer group collapsing to a single distribution independent of z.These are the first experiments to obtain all components of the lateral and vertical dispersion parameters (rms meander, relative dispersion, total dispersion) for continuous buoyant releases in a convection tank. They also are the first tank experiments to demonstrate agreement with field observations of: (1) the scaled ground-level concentration along the plume centreline, and (2) the dimensionless lateral dispersion _y/z_i of buoyant plumes.     

Re-analysis of the nuclear winter phenomenon

Summary An analysis of the report of the (U.S.) National Academy of Sciences (NAS) on atmospheric effects of a nuclear exchange leads to conclusions that differ from those of the NAS and of the earlier TTAPS and AMBIO studies. Any cooling of the earth's surface is likely to beshort-lived because of rapid removal of the smoke clouds originating from nuclear burst-initiated fires, andminor because of appreciable green-house effects due to several distinct physical causes. (One of these, neglected in prior analyses, is the infrared absorption from cirrus clouds produced directly by the nuclear bursts.) Taken together, these effects may even induce slight surface warming (nuclear summer) instead of cooling (nuclear winter). The consequences to atmospheric ozone are similarly ambiguous; depending on the detailed nuclear scenario, the net ozone content may increase-rather than decrease as argued by TTAPS. Experiments could settle some uncertainties.With 2 Figures     

Recurrence statistics of concentration fluctuations in plumes within a near-neutral atmospheric surface layer

This study examines the statistical properties of the concentration derivative, , for a dispersing plume in a near-neutrally stratified atmospheric surface layer. Towards this goal, the probability density function (pdf) of , and the conditional pdf of given a fixed concentration level, , have been measured. These pdfs are found to be modeled well by a generalizedq-Gaussian (gqG) distribution with intermittency exponent,q, equal to 0.3 and 3/4, respectively. These results highlight the strong intermittency effect (patchiness) of the small-scale concentration eddy structures in the plume. The distribution of time intervals between successive high peaks in the squared derivative process, x², is found to be well approximated by a power-law distribution, implying that occurrences of these high peaks are much more clustered than would be predicted by a Poisson or shot-noise process. The results are used to improve models for the joint pdf of and , and for the expected number of upcrossings per unit time interval of a fixed concentration level that have been proposed by Kristensenet al. (1989). The predictions of the improved models are in accord with observations, and suggest that the intercorrelation between and must be explicitly incorporated if good estimates of the upcrossing intensity are to be obtained.     

Arctic hazes in summer over Greenland and the North American Arctic. III: A contribution from the natural burning of carbonaceous materials and pyrites

Airborne measurements of the emissions from natural fires, fueled by pyrites and organic materials, at the Smoking Hills in the Northwest Territories, show that they are a regionally significant source of SO₂ (0.3 kg s^–1 or 10⁴ T yr^–1) and particles (0.3 kg s^–1). It appears likely that the Smoking Hills are a source for some of the dense, lower-level, haze layers that occur in the North American Arctic.     

Aerosols in Alaskan air masses

Results from measurements of the composition and size distribution of aerosol particles advected into central Alaska are reported. It is argued that the aerosol predominant in number, but not necessarily in mass, consists of submicron droplets of sulfuric acid. The major aerosol by mass in arctic air is a removal-resistant accumulation mode (radius 0.3 m) probably to large extent originating from pollution sources 10³ km upstream (mostly in central Eurasia) from the site in Alaska. The accumulation mode aerosol disappears when arctic air masses are replaced with relatively warmer air masses flowing in from the northern Pacific. The latter air mass systems have been strongly scavenged by clouds and precipitation associated with the Aleutian low pressure system and with forced orographic uplifting over the Alaska Mountain Range; nevertheless the Pacific air masses contain substantial (i.e., 500–1000 cm^-3) quantities of small (several hundredths of a micron in radius) particles. Arctic-derived air masses are enriched in large (i.e, 0.3 ) particles compared to Pacific Marine air masses, whereas the opposite trend is found for smaller, Aitken, particles. The smaller particles are found in greatest abundance in warmer air mass systems, presumably because of the relatively brief time since such air masses were last exposed to sunlight with attendant production of small particles from the gas phase.     

Parameterizing turbulent diffusion through the joint probability density

The convective mass flux parameterization often used in meteorological modeling expresses the vertical flux of a transported scalar as proportional to the product of the difference in mean values of the scalar in updrafts and downdrafts and their characteristic velocity. The proportionality factor is a constant to be specified. We show that this proportionality factor also appears in the relaxed eddy accumulation technique of Businger and Oncley. That associates the surface-layer flux of a scalar with the product of the standard deviation of vertical velocity and the mean concentration difference between updrafts and downdrafts.We show that this constant (b) is determined uniquely by the joint probability density (jpd) of vertical velocity and the scalar. Using large-eddy simulation, we generate this jpd for a conservative scalar diffusing through a convective boundary layer. It has quite different forms in top-down and bottom-up diffusion geometries. The bottom-up jpd is fairly well represented by a jointly Gaussian form and implies b ~ 0.6, in good agreement with the surface-layer value reported by Businger and Oncley. The top-down jpd is strikingly non-Gaussian and gives b ~ 0.47. Updrafts carry the bulk of the scalar flux - 70% in the bottom-up case, 60% in the top-down case.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Gas-Phase Ozone Oxidation of Monoterpenes: Gaseous and Particulate Products

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.     

Development of sea surface temperature,surface wind and divergence anomalies during a composite ENSO episode

Summary The interannual variations in sea surface temperature (SST) in the equatorial east Pacific, which are dominated by the El Niño phenomenon, are shown for the period 1870–1983. Since 1870 25 significant warm events have occurred. These events are classified as weak, moderate, strong and very strong, according to the normalized SST anomalies in the region 130° W–80° W, 0°–5° S.The spatial and temporal development of a composite El Niño/Southern Oscillation (ENSO) episode, based on 10 very strong or strong events, is presented in terms of SST, surface wind and divergence anomalies for the tropical Pacific (10° N–30° S). During its evolution the following phases are distinguished: Antecedent Conditions, Onset Phase, Peak Phase, Mature Phase and Dissipation Stage.Some aspects of ocean-atmosphere interaction associated with this evolution and, more specifically, the initiation of the composite event, are described. Seasonally varying feedback processes between SST, surface wind and convergence anomaly patterns in the western Pacific/Indonesian region suggest a possible mechanism for the initiation of typical ENSO events.

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Zusammenfassung Die interannuären Variationen der Meeresoberflächentemperatur (SST) im äquatorialen Ostpazifik, die von dem El Niño-Phänomen dominiert werden, werden für die Periode 1870–1983 aufgezeigt. Seit 1870 traten 25 signifikante Ereignisse auf. Diese Ereignisse werden entsprechend den normierten SST-Anomalien in der Region 130° W–80° W, 0°–5° S als schwach, mittel, stark und sehr stark klassifiziert.Die räumliche und zeitliche Entwicklung einer Komposit-El Niño/Southern Oscillation (ENSO)-Episode, die auf 10 sehr starken bzw. starken Ereignissen basiert, wird anhand von SST-, Bodenwind- und Divergenzanomalien für den tropischen Pazifik (10° N–30° S) dargestellt. Während ihrer Entwicklung werden die folgenden Phasen unterschieden: Vorausgehende Bedingungen, Einsetzphase, Spitzenphase, Reifestadium und Auflösungsstadium.Einige Aspekte der Wechselbeziehungen Ozean—Atmosphäre werden im Zusammenhang mit der Entwicklung und insbesondere der Auslösung des Komposit-Ereignisses beschrieben. Jahreszeitlich variierende Rückkopplungsprozesse zwischen SST-, Bodenwind- und Konvergenzanomalien in der westpazifischen/indonesischen Region stellen einen möglichen Mechanismus für die Auslösung typischer ENSO-Ereignisse dar.

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With 9 Figures     

Surface-Layer Fluxes in Stable Conditions

Micrometeorological tower data from the Microfronts experiment are analyzed. Scale-dependencies of the flux and flux sampling error are combined to automatically determine Reynolds turbulence cut-off time scales for computing fluxes from time series. The computed downward heat flux at the 3 m height averaged over nine nights with 7.3 hours each night is 20% greater than the downward heat flux computed at the 10 m height. In contrast, there is only a 1.2% difference between 3 m and 10 m heat fluxes averaged over daytime periods, and there is less than a 2% difference between 3 m and 10 m momentum fluxes whether averaged over nighttime or daytime periods.Stability functions, M(z/L) and H(z/L) are extended to z/L up to 10, where z is the observational height and L is the Obukhov length. For 0.01 < z/L < 1 the estimated functions generally agree with Businger-Dyer formulations, though the H estimates include more scatter compared to the M estimates. For 1 < z/L < 10, the flux intermittency increases, the flux Richardson number exceeds 0.2, and the number of flux samples decreases. Nonetheless the estimates of the stability function M based on 3-m fluxes are closer to the formula proposed by Beljaars and Holtslag in 1991 while the M functions based on 10-m fluxes appears to be closer to the formula proposed by Businger et al. in 1971. The stability function H levels off at z/L = 0.5.     

Formation of Organic Aerosols from the Oxidation of Biogenic Hydrocarbons

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.