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1.
Local Imbalance of Turbulent Kinetic Energy in the Surface Layer 总被引:1,自引:1,他引:0
We utilize experimental data collected in 2002 over an open field in Hanford, Washington, USA, to investigate the turbulent
kinetic energy (TKE) budget in the atmospheric surface layer. The von Kármán constant was determined from the near-neutral
wind profiles to be 0.36 ± 0.02 rather than the classical value of 0.4. The TKE budget was normalized and all terms were parameterized
as functions of a stability parameter z/L, where z is the distance from the ground and L is the Obukhov length. The shear production followed the Businger–Dyer relation for −2 < z/L < 1. Contrary to the traditional Monin–Obukhov similarity theory (MOST), the shear, buoyancy and dissipation terms were found
to be imbalanced due to a non-zero vertical transport over all stabilities. Motivated by this local imbalance, modified parameterizations
of the dissipation and the turbulent transport were attempted and generated good agreement with the experimental data. Assuming
stationarity and horizontal homogeneity, the pressure transport was estimated from the residual of the TKE budget. 相似文献
2.
A modification of the most popular two-equation (E–φ) models, taking into account the plant drag, is proposed. Here E is the turbulent kinetic energy (TKE) and φ is any of the following variables: El (product of E and the mixing length l),
(dissipation rate of TKE), and ω (specific dissipation of TKE,
). The proposed modification is due to the fact that the model constants estimated experimentally for ‘free-air’ flow do not allow for adequate reconstruction of the ratio between the production and dissipation rates of TKE in the vegetation canopy and have to be adjusted. The modification is universal, i.e. of the same type for all E–φ models considered. The numerical experiments carried out for both homogeneous and heterogeneous plant canopies with E–φ models (and with the E–l model taken as a kind of reference) show that the modification performs well. They also suggest that E– and E–ω schemes are more promising than the E–El scheme for canopy flow simulation since they are not limited by the need to use a wall function.In addition, a new parameterization for enhanced dissipation within the plant canopy is derived. It minimizes the model sensitivity to C
μ, the key parameter for two-equation schemes, and whose estimates unfortunately vary considerably from experiment to experiment. The comparison of results of new modified E– and E –ω models with observations from both field and wind-tunnel experiments shows that the proposed parameterization is quite robust. However, because of uncertainties with the turbulence Prandtl and Schmidt numbers for the E– model within the canopy, the E–ω model is recommended for future implementation, with the suggested modifications. 相似文献
3.
Energy- and flux-budget (EFB) turbulence closure model for stably stratified flows. Part I: steady-state,homogeneous regimes 总被引:3,自引:3,他引:0
S. S. Zilitinkevich T. Elperin N. Kleeorin I. Rogachevskii 《Boundary-Layer Meteorology》2007,125(2):167-191
We propose a new turbulence closure model based on the budget equations for the key second moments: turbulent kinetic and
potential energies: TKE and TPE (comprising the turbulent total energy: TTE = TKE + TPE) and vertical turbulent fluxes of
momentum and buoyancy (proportional to potential temperature). Besides the concept of TTE, we take into account the non-gradient
correction to the traditional buoyancy flux formulation. The proposed model permits the existence of turbulence at any gradient
Richardson number, Ri. Instead of the critical value of Richardson number separating—as is usually assumed—the turbulent and
the laminar regimes, the suggested model reveals a transitional interval, , which separates two regimes of essentially different nature but both turbulent: strong turbulence at ; and weak turbulence, capable of transporting momentum but much less efficient in transporting heat, at . Predictions from this model are consistent with available data from atmospheric and laboratory experiments, direct numerical
simulation and large-eddy simulation. 相似文献
4.
Andrey Sogachev 《Boundary-Layer Meteorology》2009,130(3):423-435
The note presents a rational approach to modelling the source/sink due to vegetation or buoyancy effects that appear in the
turbulent kinetic energy, E, equation and a supplementary equation for a length-scale determining variable, φ, when two-equation closure is applied to canopy and atmospheric boundary-layer flows. The approach implements only standard
model coefficients C
φ1 and C
φ2 in the production and destruction terms of the φ equation, respectively. Numerical tests illustrate the practical applicability of the method, where, for example, simulations
with the E–ω model (where is the specific dissipation and is the dissipation rate of E) properly reproduce both the surface-layer wind profile estimated from the Monin-Obukhov similarity theory and the mixing-height
evolution observed above forested terrain in Southern Finland. 相似文献
5.
Atmospheric measurements from several field experiments have been combined to develop a better understanding of the turbulence structure of the stable atmospheric boundary layer. Fast response wind velocity and temperature data have been recorded using 3-dimensional sonic anemometers, placed at severalheights (1 m to 4.3 m) above the ground. The measurements wereused to calculate the standard deviations of the three components of the windvelocity, temperature, turbulent kinetic energy (TKE) dissipation andtemperature variance dissipation. These data were normalized and plottedaccording to Monin–Obukhov similarity theory. The non-dimensional turbulencestatistics have been computed, in part, to investigate the generalapplicability of the concept of z-less stratification for stable conditions. From the analysis of a data set covering almost five orders ofmagnitude in the stability parameter = z/L (from near-neutral tovery stable atmospheric stability), it was found that this concept does nothold in general. It was only for the non-dimensional standard deviation oftemperature and the average dissipation rate of turbulent kinetic energythat z-less behaviour has been found. The other variables studied here(non-dimensional standard deviations of u, v, and w velocity components and dissipation of temperature variance) did not follow the concept of z-less stratification for the very stable atmospheric boundary layer. An imbalance between production and dissipation of TKE was found for the near-neutral limit approached from the stable regime, which matches with previous results for near-neutral stability approached from the unstable regime. 相似文献
6.
Turbulent Intensities and Velocity Spectra for Bare and Forested Gentle Hills: Flume Experiments 总被引:1,自引:1,他引:0
To investigate how velocity variances and spectra are modified by the simultaneous action of topography and canopy, two flume
experiments were carried out on a train of gentle cosine hills differing in surface cover. The first experiment was conducted
above a bare surface while the second experiment was conducted within and above a densely arrayed rod canopy. The velocity
variances and spectra from these two experiments were compared in the middle, inner, and near-surface layers. In the middle
layer, and for the canopy surface, longitudinal and vertical velocity variances () were in phase with the hill-induced spatial mean velocity perturbation (Δu) around the so-called background state (taken here as the longitudinal mean at a given height) as predicted by rapid distortion
theory (RDT). However, for the bare surface case, and remained out of phase with Δu by about L/2, where L is the hill half-length. In the canopy layer, wake production was a significant source of turbulent energy for , and its action was to re-align velocity variances with Δu in those layers, a mechanism completely absent for the bare surface case. Such a lower ‘boundary condition’ resulted in longitudinal
variations of to be nearly in phase with Δu above the canopy surface. In the inner and middle layers, the spectral distortions by the hill remained significant for the
background state of the bare surface case but not for the canopy surface case. In particular, in the inner and middle layers
of the bare surface case, the effective exponents derived from the locally measured power spectra diverged from their expected
− 5/3 value for inertial subrange scales. These departures spatially correlated with the hill surface. However, for the canopy
surface case, the spectral exponents were near − 5/3 above the canopy though the minor differences from − 5/3 were also
correlated with the hill surface. Inside the canopy, wake production and energy short-circuiting resulted in significant departures
from − 5/3. These departures from − 5/3 also appeared correlated with the hill surface through the wake production contribution
and its alignment with Δu. Moreover, scales commensurate with Von Karman street vorticies well described wake production scales inside the canopy,
confirming the important role of the mean flow in producing wakes. The spectra inside the canopy on the lee side of the hill,
where a negative mean flow delineated a recirculation zone, suggested that the wake production scales there were ‘broader’
when compared to their counterpart outside the recirculation zone. Inside the recirculation zone, there was significantly
more energy at higher frequencies when compared to regions outside the recirculation zone. 相似文献
7.
The Monin–Obukhov similarity theory (MOST) functions fε and fT, of the dissipation rate of turbulent kinetic energy (TKE). ε, and the structure parameter of temperature, CT2, were determined for the stable atmospheric surface layer using data gathered in the context of CASES-99. These data cover
a relatively wide stability range, i.e. ζ=z/L of up to 10, where z is the height and L the Obukhov length. The best fits were given by fε = 0.8 + 2.5ζ and fT= 4.7[ 1+1.6(ζ)2/3], which differ somewhat from previously published functions. ε was obtained from spectra of the longitudinal wind velocity
using a time series model (ARMA) method instead of the traditional Fourier transform. The neutral limit fε =0.8 implies that there is an imbalance between TKE production and dissipation in the simplified TKE budget equation. Similarly,
we found a production-dissipation imbalance for the temperature fluctuation budget equation. Correcting for the production-dissipation
imbalance, the ‘standard’ MOST functions for dimensionless wind speed and temperature gradients (φm and φm) were determined from fε and fT and compared with the φm and φh formulations of Businger and others. We found good agreement with the Beljaars and Holtslag [J. Appl. Meteorol. 30, 327–341 (1991)] relations. Lastly, the flux and gradient Richardson numbers are discussed also in terms of fε and fT. 相似文献
8.
Two-Dimensional Scalar Spectra in the Deeper Layers of a Dense and Uniform Model Canopy 总被引:1,自引:1,他引:0
The turbulent flow inside dense canopies is characterized by wake production and short-circuiting of the energy cascade. How these processes affect passive scalar concentration variability in general and their spectral properties in particular remains a vexing problem. Progress on this problem is frustrated by the shortage of high resolution spatial concentration measurements, and by the lack of simplified analytical models that connect spectral modulations in the turbulent kinetic energy (TKE) cascade to scalar spectra. Here, we report the first planar two-dimensional scalar concentration spectra (ϕ
cc
) inside tall canopies derived from flow visualization experiments. These experiments were conducted within the deeper layers of a model canopy composed of densely arrayed cylinders welded to the bottom of a large recirculating water channel. We found that in the spectral region experiencing wake production, the ϕ
cc
exhibits directional scaling power laws. In the longitudinal direction (x), or the direction experiencing the largest drag force, the ϕ
cc
(k
x
) was steeper than and followed an approximate at wavenumbers larger than the injection scale of wake energy, where k
x
is the longitudinal wavenumber. In the lateral direction (y), the spectra scaled as up to the injection scale, and then decayed at an approximate
power law. This departure from the classical inertial subrange scaling (i.e., k
−5/3) was reproduced using a newly proposed analytical solution to a simplified scalar spectral budget equation. Near the velocity viscous dissipation range, the scalar spectra appear to approach an approximate k
−3, a tantalizing result consistent with dimensional analysis used in the inertial-diffusive range. Implications to subgrid modelling for large-eddy simulations (LES) inside canopies are briefly discussed. 相似文献
9.
Local Similarity in the Stable Boundary Layer and Mixing-Length Approaches: Consistency of Concepts 总被引:2,自引:1,他引:1
B. J. H. van de Wiel A. F. Moene W. H. De Ronde H. J. J. Jonker 《Boundary-Layer Meteorology》2008,128(1):103-116
In stably stratified flows vertical movement of eddies is limited by the fact that kinetic energy is converted into potential
energy, leading to a buoyancy displacement scale z
B
. Our new mixing-length concept for turbulent transport in the stable boundary layer follows a rigid-wall analogy, in the sense that we assume that the buoyancy length scale is similar to neutral length scaling. This implies that the buoyancy
length scale is: ℓ
B
= κ
B
z
B
, with κ
B
≈ κ, the von Karman constant. With this concept it is shown that the physical relevance of the local scaling parameter z/Λ naturally appears, and that the α coefficient of the log-linear similarity functions is equal to c/κ
2, where c is a constant close to unity. The predicted value α ≈ 1/κ
2 = 6.25 lies within the range found in observational studies. Finally, it is shown that the traditionally used inverse linear
interpolation between the mixing length in the neutral and buoyancy limits is inconsistent with the classical log-linear stability
functions. As an alternative, a log-linear consistent interpolation method is proposed. 相似文献
10.
A comprehensive model for the prediction of concentration fluctuations in plumes dispersing in the complex and highly disturbed
wind flows in an urban environment is formulated. The mean flow and turbulence fields in the urban area are obtained using
a Reynolds-averaged Navier-Stokes (RANS) flow model, while the standard k-ϵ turbulence model (k is the turbulence kinetic energy and ϵ is the viscous dissipation rate) is used to close the model. The RANS model provides a specification of the velocity statistics
of the highly disturbed wind flow in the urban area, required for the solution of the transport equations for the mean concentration
and concentration variance (both of which are formulated in the Eulerian framework). A physically-based formulation for the scalar dissipation time
scale t
d
, required for the closure of the transport equation for , is presented. This formulation relates t
d
to an inner time scale corresponding to “internal” concentration fluctuation associated with relative dispersion, rather
than an outer time scale associated with the entire portion of the fluctuation spectrum. The two lowest-order moments of concentration
( and ) are used to determine the parameters of a pre-chosen functional form for the concentration probability density function
(clipped-gamma distribution). Results of detailed comparisons between a water-channel experiment of flow and dispersion in
an idealized obstacle array and the model predictions for mean flow, turbulence kinetic energy, mean concentration, concentration
variance, and concentration probability density function are presented. 相似文献
11.
We present surface-layer measurements of temperature fluctuation variance from a site characterized by small-scale inhomogeneities.
Periods of marked radiative forcing are selected. The data characterized by diabatic conditions and vertical heat flux larger
than some threshold (here, chosen to be 0.01 K ms−1) agree quite well with the convective scaling in unstable cases, and with the z-less parameterisation (with a large scatter) in stable cases. For near-neutral cases, the similarity function diverges because of the loss of significance
of the temperature scale. Departures from similarity are highlighted in cases with smaller thermal fluxes, because horizontal
heterogeneity and unsteadiness become important as production terms. 相似文献
12.
Time Scales in the Unstable Atmospheric Surface Layer 总被引:2,自引:2,他引:0
Calculation of eddy covariances in the atmospheric surface layer (ASL) requires separating the instantaneous signal into mean
and fluctuating components. Since the ASL is not statistically stationary, an inherent ambiguity exists in defining the mean
quantities. The present study compares four methods of calculating physically relevant time scales in the unstable ASL that
may be used to remove the unsteady mean components of instantaneous time signals, in order to yield local turbulent fluxes
that appear to be statistically stationary. The four mean-removal time scales are: (t
c
) based on the location of the maximum in the ogive of the heat flux cospectra, () the location of the zero crossing in the multiresolution decomposition of the heat flux, (t
*) the ratio of the mixed-layer depth over the convective velocity, and () the convergence time of the vertical velocity and temperature variances. The four time scales are evaluated using high quality,
three-dimensional sonic anemometry data acquired at the Surface Layer Turbulence and Environmental Science Test (SLTEST) facility
located on the salt flats of Utah’s western desert. Results indicate that and , with t
c
achieving values about 2–3 times greater than t
*. The sensitivity of the eddy covariances to the mean-removal time scale (given a fixed 4-h averaging period during midday)
is also demonstrated. 相似文献
13.
In order to quantitatively investigate the role of leads and sea-ice in air-mass modification, aircraft observations were
conducted over the partially ice-covered Sea of Okhotsk. We investigated two cold-air outbreak events with different sea-ice
concentrations. In both cases, the difference between the temperatures of surface air and the sea surface (ΔT) dropped rapidly with the accumulated fetch-width of leads up to about 35-40 km, and then decreased very slowly. The surface
sensible heat flux originating from open water was about 300 W m−2 within a few kilometres from the coast and decreased with increasing accumulated fetch-width. The sensible heat flux was
about 100 W m−2 on average. These results indicate that the downwind air-mass modification depends mainly on the total (accumulated) extent
of open water. The total buoyancy flux
calculated by the joint frequency distribution method correlated very well with ice concentration. Such a relationship was
not clear in the case of the moisture flux
. The ratio between rising thermals
and cold downdrafts
differed significantly between upwind and downwind regions; that is, the buoyancy flux was dominated by
in the developing stage of the boundary layer, while
also became important after the development of the boundary layer. 相似文献
14.
Laura T. Iraci Brent G. Riffel Carly B. Robinson Rebecca R. Michelsen Rachel M. Stephenson 《Journal of Atmospheric Chemistry》2007,58(3):253-266
The aqueous phase acid-catalyzed reaction of methanol (CH3OH) with nitric acid (HNO3) to yield methyl nitrate (CH3ONO2) under atmospheric conditions has been investigated using gas-phase infrared spectroscopy. Reactions were conducted in aqueous
sulfuric acid solutions (50.5–63.6 wt.%) with [CH3OH] = 0.00005–0.005 M and [HNO3] = 0.02–0.21 M, at 278.2–328.6 K. Methyl nitrate production rates increased linearly with CH3OH and HNO3 concentrations and exponentially with sulfuric acid weight percent within the regime studied. Rates increased linearly with
nitronium ion concentration, indicating that the reaction involves as the nitrating agent under these conditions. At 298 K, the rate of methyl nitrate production can be calculated from k
obs
[CH3OH][HNO3], where k
obs
= 2.337 × 10−13(exp(0.3198*wt.% H2SO4)) when the solubility of CH3ONO2 in acidic solution is approximated by H* for pure water. The temperature dependence of the rate coefficient is related to solution composition, with activation energies
of 59 and 49 kJ/mol at 51.1 and 63.6 wt.% H2SO4, respectively, when k is calculated from rate. The temperature dependence has also been parameterized for application to the atmosphere, but the small quantities of present in aerosol particles will result in methyl nitrate production rates too small to be of significance under most atmospheric
conditions.
An erratum to this article can be found at 相似文献
15.
A one-dimensional numerical model based on the equations of mean motion and turbulent kinetic energy (TKE), with Delage's (1974) mixing-length parameterization has been used to simulate the mean and turbulent structure of the evolving stably stratified nocturnal boundary layer (NBL). The model also includes a predictive equation for the surface temperature and longwave radiational cooling effects.In the absence of advective and gravity wave effects, it is found that the model-simulated structure, after a few hours of evolution, could be ordered fairly well by a similarity scaling (u
*0, *0, L
0, and h) based on surface fluxes and the NBL height. Simple expressions are suggested to describe the normalized profiles of momentum and heat fluxes, TKE, eddy-viscosity and energy dissipation. A good ordering of the same variables is also achieved by a local scaling (u
*0, * and L) based on the height-dependent local fluxes. The normalized TKE, eddy viscosity and energy dissipation are unique functions of z/L and approach constant values as z/L , where L is the local Monin-Obukhov length. These constants are close to the values predicted for the surface layer as z/L , thus suggesting that the Monin-Obukhov similarity theory can be extended to the whole NBL, by using the local (height-dependent) scales in place of surface-layer scales. The observed NBL structure has been shown to follow local similarity (Nieuwstadt, 1984). 相似文献
16.
The precipitation events (n = 91), collected for 3 years (2000–2002) during the period of SW-monsoon (Jun–Aug) from an urban
site (Ahmedabad, 23.0°N, 72.6°E) of a semi-arid region in western India, are found to exhibit characteristic differences in
terms of their solute contents. The low solute (<700 μeq L−1) events are either marked by heavy precipitation amount or successive events collected during an extended rain spell; whereas
light precipitation events occurring after antecedent dry period are characterized by high solutes (>700 μeq L−1). The ionic composition of low solute events show large variability due to varying contribution of anthropogenic species
(: 1%–74%; : 1%–25%; and : 8%–68%) to the respective ion balance. In high solute events, ionic abundances are dominated by mineral dust (Ca2+ and ) and sea-salts (Na+ and Cl−). These differences are also reflected in the pH of low solute events (range: 5.2–7.4, VWM: 6.4) and high solute events (range:
6.6–8.2, VWM: 7.3). The comparison of Ca2+/Na+ and nss- ratios (on equivalent basis) in rain and aerosols suggests that the ionic composition of high solute events is influenced
by below-cloud scavenging; whereas evidence for in-cloud scavenging is significantly reflected in low solute events. The annual
wet-deposition fluxes of and are 330 and 480 mg m−2 y−1, respectively, in contrast to their corresponding dry-deposition fluxes (14 and 160 mg m−2 y−1); whereas wet and dry removal of Ca2+, Mg2+ and are comparable. 相似文献
17.
Boštjan Podkrajšek Gorazd Berčič Janja Turšič Irena Grgić 《Journal of Atmospheric Chemistry》2004,47(3):287-303
The reaction kinetics of S(IV) autoxidation catalyzed by Mn(II) in the pH range 3–5 typical for atmospheric liquid water,
was investigated. For reactions with pH maintained constant during the reaction course, the predictions obtained by a simple
integral approach cover kinetic results only for concentrations of HSO
3
−
up to 0.2 mM at pH 4.5. Thus, a generalized simple kinetic model, which can be used for predicting the reaction kinetics
in wider concentration, pH and temperature ranges, was derived. This model is based on the assumption that the reaction rate
is proportional to the concentration of a transient manganese-sulfito complex formed in the initial step of a radical chain
mechanism. In the proposed power law rate equation
the concentration of complex is calculated from the stability constant K and concentrations of reactants at a specific reaction time. This rate equation adequately predicts the reaction kinetics
in the pH range 3–5, in the concentration ranges 0.1 ≤ [HSO
3
−
] ≤ 0.4 mM and 2 ≤ [Mn(II)] ≤ 14.6 μM. For the temperature range 15–35 °C, the estimated value for activation energy is 92.0
± 0.1 kJ mol−1 and the Gibbs free energy of formation of the manganese-sulfito complex is −20.4 ± 0.3 kJ mol−1. Furthermore, the kinetics for catalytic reactions with pH maintained constant during the reaction course as well as with
initial pH adjusted only at the start of the reaction, is described satisfactorily by the present model. 相似文献
18.
We describe one-dimensional (1D) simulations of the countergradient zone of mean potential temperature observed in the convective boundary layer (CBL). The method takes into account the third-order moments (TOMs) in a turbulent scheme of relatively low order, using the turbulent kinetic energy equation but without prognostic equations for other second-order moments. The countergradient term is formally linked to the third-order moments and , and a simple parameterization of these TOMs is proposed. It is validated for several cases of a dry CBL, using large-eddy simulations that have been realized from the MESO-NH model. The analysis of the simulations shows that TOMs are responsible for the inversion of the sign of in the higher part of the CBL, and budget analysis shows that the main terms responsible for turbulent fluxes and variances are now well reproduced. 相似文献
19.
Observed winds,turbulence, and dispersion in built-up downtown areas of Oklahoma City and Manhattan 总被引:2,自引:2,他引:0
Wind and tracer data from the Oklahoma City Joint Urban 2003 (JU2003) and the Manhattan Madison Square Garden 2005 (MSG05)
urban field experiments are being analyzed to aid in understanding air flow and dispersion near street-level in built-up downtown
areas. The mean winds are separately calculated for groups of anemometers having similar exposures such as “near street level”
and “on building top”. Several general results are found, such as the scalar wind speed at street level is about 1/3 of that
at building top. Turbulent standard deviations of wind speed components and temperature, and vertical fluxes of momentum and
sensible heat, are calculated from sonic anemometers near street level at 20 locations in JU2003 and five locations in MSG05,
and from two rooftop locations in MSG05. The turbulence observations are consistent with observations in the literature at
other cities, although the JU2003 and MSG05 data are unique in that many data are available near street level. For example,
it is found that the local (i.e., at the measuring height) averages about 1.5 and the local averages about 0.25 in the two cities, where is the standard deviation of vertical velocity fluctuations, is the friction velocity, and u is the wind speed. The ratio of temperature fluctuations to temperature scale, , averages about −3 in both cities, consistent with similarity theory for slightly unstable conditions, where is the standard deviation of temperature fluctuations, and is the temperature scale. The calculated Obukhov length, L, is also consistent with slightly unstable conditions near street level, even at night during JU2003. The SF6 tracer concentration observations from JU2003 are analyzed. Values of for the continuous releases are calculated for each release and arc distance, where is the 30-min average arc maximum concentration, Q is the continuous source emission rate, and u is the spatial-averaged wind speed in the downtown area. The basic characteristics of the JU2003 plot of averaged agree reasonably well with similar plots for other urban experiments in Salt Lake City and London (i.e., at . A is found to be about 3 during the day and about 10 during the night. 相似文献
20.
N. Carrasco J. F. Doussin M. O’Connor J. C. Wenger B. Picquet-Varrault R. Durand-Jolibois P. Carlier 《Journal of Atmospheric Chemistry》2007,56(1):33-55
This article presents a complete study of the diurnal chemical reactivity of the biogenic volatile organic compound (BVOC), 2-methyl-3-buten-2-ol (MBO) in the troposphere. Reactions of MBO with OH and with ozone were studied to analyse the respective parts of both processes in the global budget of MBO atmospheric reactivity. They were investigated under controlled conditions for pressure (atmospheric pressure) and temperature (298 ± 2 K) using three complementary European simulation chambers. Reaction with OH radicals was studied in the presence of and in the absence of NO
x
. The kinetic study was carried out by relative rate study using isoprene as a reference. The rate constant found for this reaction was molecule−1 cm3 s−1. FTIR spectroscopy, DNPH- and PFBHA-derivatisation analyses were performed for reactions with both OH radicals and ozone. In both reactions, the hydroxycarbonyl compound, 2-hydroxy-2-methylpropanal (HMPr) was positively identified and quantified, with a yield of in the reaction with OH, and a yield of and 0.84 ± 0.08 in the reaction with ozone under dry (HR < 1%) and humid conditions (HR = 20%–30%). A primary production of two other carbonyl compounds, acetone , and formaldehyde was found in the case of the dry ozonolysis experiments. Under humid conditions, only formaldehyde was co-produced with HMPr as a primary carbonyl compound, with a yield of . For the reaction with OH, three other carbonyl compounds were detected, acetone , formaldehyde and glycolaldehyde . In addition some realistic photo-oxidation experiments were performed to understand in an overall way the transformations of MBO in the atmosphere. The realistic photo-oxidation experiments were conducted in the EUPHORE outdoor simulation chamber. It was found that this compound is a weak secondary aerosol producer (less than 1% of the carbon balance). But it was confirmed that it is a potentially significant source of acetone, Δ[Acetone]/Δ[MBO] = 0.45. With our experimental conditions ([MBO]0 = 200 ppb, [NO]o = 50 ppb), an ozone yield of Δ[O3]/Δ[MBO] = 1.05 was found. 相似文献