Ozone Dry Deposition Research Articles

Effect of the soil wetness state on the stomatal ozone fluxes over Hungary

A coupled Eulerian photochemical reaction-transport model and a detailed ozone dry deposition model have been utilised for the estimation of stomatal ozone fluxes over Hungary. Ozone concentrations were modelled on an unstructured triangular grid using a method of lines approach to the solution of the reaction-diffusion-advection equations describing ozone formation, transport and deposition. The model domain covers Central-Europe including Hungary, which was located at the centre of the domain and covered by a high resolution nested grid. The dry deposition velocity of ozone was calculated based on the aerodynamic, quasi-laminar boundary layer and canopy resistance. The effect of soil water content on the stomatal ozone flux was analysed. The stomatal ozone flux calculations were performed for two cases, with and without taking into account the effect of the soil moisture stress on the ozone deposition. The meteorological data were generated by the ALADIN meso-scale limited area numerical weather prediction model. It was found that soil water deficiency can strongly reduce the stomatal conductance and hence the ozone flux through it.

Sensitivity analysis of an ozone deposition model

In this study, sophisticated sensitivity analyses of a detailed ozone dry deposition model were performed for five soil types (sand, sandy loam, loam, clay loam, clay) and four land use categories (agricultural land, grass, coniferous and deciduous forests). Deposition velocity and ozone flux depend on the weather situation, physiological state of the plants and numerous surface-, vegetation-, and soil-dependent parameters. The input data and the parameters of deposition-related calculations all have higher or lower spatial and temporal variability. We have investigated the effect of the variability of the meteorological data (cloudiness, relative humidity and air temperature), plant-dependent (leaf area index and maximum stomatal conductance) and soil-dependent (soil moisture) parameters on ozone deposition velocity. To evaluate this effect, two global methods, the Morris method and the Monte Carlo analysis with Latin hypercube sampling were applied. Additionally, local sensitivity analyses were performed to estimate the contribution of non-stomatal resistances to deposition velocity. Using the Monte Carlo simulations, the ensemble effect of several nonlinear processes can be recognised and described. Based on the results of the Morris method, the individual effects on deposition velocity are found to be significant in the case of soil moisture and maximum stomatal conductance. Temperature and leaf area index are also important factors; the former is primarily in the case of agricultural land, while the latter is for grass and coniferous forest. The results of local sensitivity analyses reveal the importance of non-stomatal resistances.

Modeling the effect of iodide distribution on ozone deposition to seawater surface

Spatial changes in the dry deposition of ozone to the sea surface associated with ozone uptake by the dissolved iodide ions were analyzed in the northwestern Gulf of Mexico using the Community Multiscale Air Quality Model (CMAQ). The dry deposition module in CMAQ was modified using a formula developed by Chang et al. [2004. Ozone deposition to the sea surface: chemical enhancement and wind speed dependence. Atmospheric Environment 38, 1053–1059], which accounts for chemical enhancement by iodide reacting with ozone in seawater. In addition, an attempt was made to incorporate iodide concentrations from the satellite-derived estimates of near-surface chlorophyll a concentrations into the CMAQ gridded fields. One-month CMAQ simulations conducted with the modified module including iodide reaction showed a significant increase in the dry deposition velocity of ozone onto the sea surface, especially Texas and Louisiana Coast corresponding to the area with high iodide concentrations. On average, about 70% enhancement of ozone dry deposition velocity over the seawater was attributed to the iodide effect alone and the rest is mostly due to the effects of wind. The enhanced deposition velocity by iodide effect led to the marked increase in dry deposition amounts mostly near the coast, resulting in some changes in ambient ozone concentration. Interestingly, a small decrease in deposition amounts was found just inland from the shoreline, indicating that the iodide interaction can also affect ozone concentration in the inland coastal area. An in-depth analysis of a 2-day simulation showed the iodide effects on changes in the spatiotemporal distributions of the ozone deposition and concentration, which are highly dependent on coastal winds.

Laboratory Measurement of Dry Deposition of Ozone onto Northern Chinese Soil Samples

We used laboratory experiments to investigate surface resistance (R c) to dry deposition of ozone (O3) on different types of soil samples collected from the arid deserts and the Loess Plateau of northern China. Furthermore, we measured the factors that affected R c, which depends on the physical and chemical interaction between trace constituents and the deposition surface, and evaluated deposition velocity (V d). There was little influence of geometric surface area, soil weight, or O3 concentration on V d of O3. The effect of relative humidity (RH) (i.e. moisture content of the soil) on O3 uptake was in agreement with results reported in the literature: a distinct RH dependence of V d and little uptake under water-saturated conditions were observed. R c values for all the soil samples examined were in the range 0.21–3.3 s mm−1 and were exponentially related to the surface area of the particles and the organic carbon content of each soil sample at RH of both <10 and 60%.

Coupled carbon-water exchange of the Amazon rain forest, II. Comparison of predicted and observed seasonal exchange of energy, CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, isoprene and ozone at a remote site in Rondônia

Abstract. A one-dimensional multi-layer scheme describing the coupled exchange of energy and CO2, the emission of isoprene and the dry deposition of ozone is applied to a rain forest canopy in southwest Amazonia. The model was constrained using mean diel cycles of micrometeorological quantities observed during two periods in the wet and dry season 1999. Calculated net fluxes and concentration profiles for both seasonal periods are compared to observations made at two nearby towers. The modeled day- and nighttime thermal stratification of the canopy layer is consistent with observations in dense canopies. The observed and modeled net fluxes above and H2O and CO2 concentration profiles within the canopy show a good agreement. The predicted net carbon sink decreases from 2.5 t C ha-1 yr-1 for wet season conditions to 1 t C ha-1 yr-1 for dry season conditions, whereas observed and modeled midday Bowen ratio increases from 0.5 to 0.8. The evaluation results confirmed a seasonal variability of leaf physiological parameters, as already suggested in a companion study. The calculated midday canopy net flux of isoprene increased from 7.1 mg C m-2 h-1 during the wet season to 11.4 mg C m-2 h-1 during the late dry season. Applying a constant emission capacity in all canopy layers, resulted in a disagreement between observed and simulated profiles of isoprene concentrations, suggesting a smaller emission capacity of shade adapted leaves and deposition to the soil or leaf surfaces. Assuming a strong light acclimation of emission capacity, equivalent to a 66% reduction of the standard emission factor for leaves in the lower canopy, resulted in a better agreement of observed and modeled concentration profiles and a 30% reduction of the canopy net flux compared to model calculations with a constant emission factor. The mean calculated ozone flux for dry season conditions at noontime was ≈12 n mol m-2 s-1, agreeing well with observed values. The corresponding deposition velocity increased from 0.8 cm s-1 to &gt;1.6 cm s-1 in the wet season, which can not be explained by increased stomatal uptake. Considering reasonable physiological changes in stomatal regulation, the modeled value was not larger than 1.05 cm s-1. Instead, the observed fluxes could be explained with the model by decreasing the cuticular resistance to ozone deposition from 5000 to 1000 s m-1.

Ozone dry deposition above a tropical forest in the dry season in northern Thailand

In order to investigate the ozone dry deposition above a tropical forest in Southeast Asia, the field experiments were performed in a flat deciduous (teak) forest in Mea Moh located in northern Thailand, in the dry season, from January to April 2002. The experimental period included both the leafless period and transitional period between lush and leafless. Ozone fluxes were obtained by coupling a UV photometric ozone monitor with an ultrasonic anemometer on the basis of the gradient method. Ozone concentrations exceeded 60 ppb on average in the afternoons during the experimental period. The ozone fluxes peak around noon. The daytime level of the fluxes in this study is relatively high compared with the fluxes from previous experiments over a tropical forest or a leafless deciduous forest in other regions. This high daytime flux level is mainly caused by the high concentrations in the dry season in Mae Moh. Median deposition velocities of ozone were 0.32 cm s−1 in daytime (6:00–17:00) and 0.04 cm s−1 in nighttime (18:00–5:00), respectively. The deposition velocities as well as the fluxes peaks around noon. Observed surface resistances decreased in daytime. The surface resistances were found to be affected by aerodynamic process rather than stomatal process during the time from 10:00 to 2:00. Wesely's parameterization to infer surface resistance was examined to consider its applicability in the region. The observed surface resistance in the dry season is closer to the inferred surface resistance using the input resistances of transitional spring than that using the input resistances of leafless seasons. This indicates that the parameterization of non-stomatal resistances needs modification above the teak forest in the dry season taking into account the influence of aerodynamic process and the specific conditions in northern Thailand.

Measurements of sulfur dioxide and ozone dry deposition over short vegetation in northern China—a preliminary study

We measured dry deposition fluxes of SO2 and O3 over a field covered mostly with short grass in a suburb of Beijing during late summer and early winter as an initiatory attempt to obtain information on dry deposition in northern China. The measurement was based on a micrometeorological gradient method, and only the data conforming to neutral atmospheric stability were analyzed because the data we collected were not adequate to extend the analysis to other stability cases. The data were further screened out according to a few selection criteria to ensure their credibility. For the selected periods Vd (deposition velocity) of SO2 showed a maximum in the morning and a minimum in the afternoon, with little seasonal dependence in this behavior. The mean (±standard deviation) Vd was 0.2 (±0.1) cm s−1 in late summer and 0.4 (±0.2) cm s−1 in early winter. The diurnal variation of Vd seemed to be more or less governed by that of Ra (aerodynamic resistance) +Rb (quasi-laminar boundary layer resistance), which was considerably larger than Rc (canopy resistance). The mean (±standard deviation) Vd of O3 was 0.2 (±0.2) cm s−1 in late summer and 0.4 (±0.3) cm s−1 in early winter, thus much the same as those for SO2. The variation of O3 Vd was qualitatively similar to that of SO2, but in this case Rc was comparable to or larger than Ra+Rb. Little distinct seasonal dependence was evident for O3 deposition, either. A tendency was discernible for Rc to increase in the afternoon, which was probably caused by a decline in stomatal conductance due to an increase in vapor pressure deficit and/or a rise in temperature.

The interfacial mass transfer resistances of the ozone dry deposition over the field soil of Taichung County in Taiwan.

This study aims to design a dry deposition chamber and to measure ozone depletion over the Taichung field soil. This study seeks to verify the phenomena by an experimental and mathematical model. It is demonstrated that interfacial mass transfer resistances of ozone dry deposition involve reactive resistance (R(sr)) and kinetic resistance (R(sk)). It reveals the chemical reaction (O3 + NO --> NO2) to produce the reactive resistance, and verifies that the interfacial mass transfer resistances depend on nitrogen oxide emission and soil temperature. It shows that the interfacial mass transfer resistances are reduced with increasing soil temperature (T(S)). The model profiles are smaller than the observed data within a relative error of 15%. The reactive resistance decreases exponentially with increasing soil temperature; R(sr)(-1) (cm x sec(-1)) = 0.0001 exp (0.1455T(S)). The kinetic resistance decreases linearly with increasing soil temperature; R(sk)(-1)(cm x sec(-1)) = 0.0108T(S) + 1.4012. This model is more accurate with higher soil temperature and larger ozone concentration. Results are consistent with thermodynamics and reaction kinetics. Ozone dry deposition over agricultural soil causes conversion of nitrogen oxide (NO) to nitrogen dioxide (NO2).

On ozone dry deposition—with emphasis on non-stomatal uptake and wet canopies

Measurements of O 3 fluxes and concentrations over five different sites were used to study O 3 dry deposition. It was found that high humidity, dew and rain increase O 3 uptake by canopy cuticles. However, the increase by cuticle uptake maybe offset by a decrease in stomatal uptake due to weak solar radiation or stomatal blocking under wet conditions. Thus, during nighttime the overall canopy resistances ( R c) for O 3 uptake under wet conditions was usually smaller than under dry conditions, while in the daytime, R c for wet canopies could be either larger or smaller compared to dry canopies. This will depend on the relative contributions of the decrease in cuticle resistance and the increase in stomatal resistance. The non-stomatal uptake of O 3 was found to be affected by friction velocity, relative humidity, canopy wetness, leaf area index, etc. Parameterizations for non-stomatal resistance for dry and wet canopies were developed based on the five site O 3 flux data. These equations were found to provide reasonable predictions of non-stomatal canopy resistance based upon comparisons with the nighttime and daytime measurements.

INTERFACIAL TRANSFER VELOCITIES OF OZONE DRY DEPOSITION OVER AGRICULTURAL SOILS: EXPERIMENTAL AND THEORETICAL ANALYSIS

A mathematical dry deposition model was developed and an experiment performed to verify that the interfacial transfer velocity (VS) of ozone dry deposition includes the interfacial reactive velocity (VSr) and interfacial kinetic velocity (VSk), as determined by measuring the ozone depletion over agricultural field soils in a dry deposition chamber. Experimental results indicate that the chemical reaction (O3+NO→NO2+O2) produces the reactive velocity. Observed interfacial transfer velocities depend on nitrogen oxide emission (NO) and soil temperature (TS). Additionally, observed kinetic velocities of conditioned field soils increased linearly with soil temperature. Moreover, observed reactive velocities of field soils increased exponentially with soil temperature, and depend on the emission rate of nitrogen oxide. Results in this study demonstrate that interfacial transfer velocities are variable velocities for long-term transportation, that influenced factors are chemical kinetics, thermodynamics and biochemical mechanisms.

Interfacial Transfer Resistances of Ozone Dry Deposition Over Agricultural Soil of Tainan County, Taiwan

A dry deposition chamber was constructed to measure ozone depletion over field soil and compared with the mathematical model that was derived in this study. Results verify that interfacial transfer resistance (RS) of ozone dry deposition involves both the reactive resistance (RSr) and the kinetic resistance (RSk). The reactive resistance is produced by the chemical reaction O3 + NO → NO2 + O2. Interfacial transfer resistance depends on the emission of nitrogen oxide (NO) and soil temperature (TS). The kinetic resistance depends on soil temperature. Model ozone profiles were smaller than the observed data (deposition curve), and within relative errors of 12%. NO emission flux (FNO) was increased exponentially with increasing soil temperature. Observed RSk decreased linearly with increasing soil temperature. Both observed RS and RSr decreased exponentially with increasing soil temperature, and RS was affected by RSr. Observed RSr approaches first-order kinetics, and regenerates nitrogen dioxide (NO2) which influences the air quality.

Ozone fluxes above and within a pine forest canopy in dry and wet conditions

The physiological and physical processes controlling ozone dry deposition to vegetated surfaces are still not fully understood. In particular, the role of the understorey and the possible action of dew on ozone deposition have not received much attention so far. This paper presents the results of an experiment aimed at quantifying ozone dry deposition to a maritime pine forest in the “Les Landes” area in France. Ozone deposition fluxes were measured using the eddy-covariance technique above and within the canopy. We investigate the factors acting on ozone deposition in both dew-wetted and dry conditions. The values obtained for the ozone deposition velocity are well in the range of previously published measurements over coniferous forests. For the present forest, ozone uptake by the understorey is a significant portion of ozone deposition to the whole pine stand. The understorey contributes more to the overall ozone flux than to the other measured scalar fluxes (sensible heat and water vapour). During dry nights the surface conductance for ozone and the friction velocity are strongly correlated, showing that ozone deposition is largely controlled by dynamical processes. During the day, in dry conditions, the canopy stomatal conductance is the major parameter controlling ozone deposition. However, in winter, when the stomatal conductance is low, the influence of dynamical processes persists during day-time. It is also found that surface wetness associated with dew significantly enhances ozone deposition, during the night as well as in the morning.

Ozone Deposition at a Forest Site in NE Bavaria

The dry deposition of ozone to aconiferous forest in northeastern Bavaria(southern Germany) was quantified during 1999with both the eddy correlation method and a bigleaf model. The model included parameterizationsof the atmospheric transfer resistances fromdirect measurements, stomatal resistance from aplant ecological model, and an estimation of thecuticle resistance as function of leaf wetness.Early in the season, the measured and themodelled deposition fluxes were in goodagreement, although the modelled fluxes tended tounderestimate the measured ones. Thisunderestimation was more pronounced in the latesummer, when high nocturnal fluxes werefrequently measured. The model parameterizationof the cuticle and the stomatal resistances didnot allow for such high fluxes. In these cases,the 24 hour average of the measured fluxes wereup to 4.5 times higher than the modelled ones.The reasons for these large discrepancies remainunknown. However, assigning the unaccounted partof the deposition to a non‐stomatal surfacedeposition pathway, a new parameterization of therespective resistance yielded an average value of300 s m-1. It exhibited a decreasing trendthrough the vegetation period.

A COUPLED LAND-SURFACE AND DRY DEPOSITION MODEL AND COMPARISON TO FIELD MEASUREMENTS OF SURFACE HEAT, MOISTURE, AND OZONE FLUXES

We have developed a coupled land-surface and drydeposition model for realistic treatment of surface fluxes ofheat, moisture, and chemical dry deposition within acomprehensive air quality modelling system. A new land-surfacemodel (LSM) with explicit treatment of soil moisture andevapotranspiration and an indirect soil moisture nudging schemehas been added to a mesoscale meteorology model. The new drydeposition model uses the same aerodynamic and bulk stomatalresistances computed for evapotranspiration in the LSM. Thisprovides consistent land-surface and boundary layer propertiesacross the meteorological and chemical components of the system. The coupled dry deposition model also has the advantage of beingable to respond to changing soil moisture and vegetationconditions. Modelled surface fluxes of sensible and latent heatas well as ozone dry deposition velocities were compared to twofield experiments: a soybean field in Kentucky during summer 1995and a mixed forest in the Adirondacks of New York in July 1998.

Ozone Dry Deposition Velocities for Coastal Waters

Air-sea exchange rates for ozone were measured by the eddy correlation technique at a site on the north Norfolk coast in the UK. The average surface resistance to ozone uptake was found to be, rs(O3) = 1,000 ± 100 s m-1. Micrometeorological measurements of trace gas fluxes to ocean surfaces are rare but a review of available measurements suggests that we can constrain sea water surface resistance for ozone to between 1,000 (Regener (1974), and this work) and 1,890 s m-1 (Lenschow et al., 1982), yielding surface deposition velocities between 0.53 and 1.0 mm s-1. These values are more than an order of magnitude greater than can be explained by laboratory determined mass accommodation coefficients for ozone to water. The importance of dry deposition with respect to process air-sea exchange models is highlighted. A trend in surface deposition velocity with wind speed was also observed supporting a surface chemical enhancement mechanism of ozone uptake which in turn is enhanced by near surface mixing processes.

Seasonal variability of ozone dry deposition under southern European climate conditions, in Portugal

Ozone dry deposition measurements were carried out during approximately one year over a flat grass field in Portugal. The results show prominent diurnal and seasonal patterns in deposition flux, dry deposition velocity and surface resistance, especially for the daytime period. Dry deposition velocities vary diurnally from a minimum of 0.1 cm s −1, during the night to a maximum of 0.2–0.5 cm s −1 during the day. The observed canopy resistance ( R c) varies from values higher than 500 s m −1, at night, to a minimum of 200 s m −1, around noon. Seasonal variation is characterised by daytime R c values much larger in summer than in winter and spring, while nighttime values do not show any evident seasonal pattern. This behaviour can be ascribed to the stomatal intake, which represents the most important controlling factor on ozone dry deposition. The Wesely parameterisation scheme of surface resistance predicts R c diurnal cycles reasonably well. However, the observed canopy resistance seasonal cycle is completely different from Wesely predictions, since season parameters in Wesely's parameterisation were defined for a vegetation growing cycle different from that prevailing in our conditions.

Assimilation of total ozone satellite measurements in a three‐dimensional tracer transport model

The optimal‐interpolation data‐assimilation technique is used to combine TIROS Operational Vertical Sounder total‐ozone columns with the three‐dimensional tracer transport model TM3. An ozone chemistry parametrization and dry deposition of ozone are added to the model to give it the ability to simulate realistic ozone profiles. Starting from a separable form of the forecast covariance matrix, the optimal interpolation equation can be rewritten into a horizontal and vertical analysis step. First, the two‐dimensional ozone column measurements are analyzed using estimates for the horizontal error covariances. In the second step of the assimilation procedure the analysis increment for the column is distributed over the vertical model layers. This step depends only on a normalized vertical weight function which is equal to the vertical covariance. Three different estimates for this weight function are introduced, using either the ozone error covariance, or the ozone time variance, or the actual ozone mass to distribute column corrections in the vertical. A comparison with independent Total Ozone Mapping Spectrometer ozone observations shows a considerable improvement of the total ozone field due to assimilation. The model error growth is small, making it suitable for assimilating sparse measurements. Ozone profiles from the assimilation appear realistic and close to the ones observed by sondes. They are capable to describe dynamical features in the lower stratosphere. However, due to the absence of vertical information, the assimilation of ozone columns has only little impact on the shape of the vertical ozone profile, which is mainly determined by the transport.

Ozone Dry Deposition and Resistances onto Green Grassland in Summer in Central Spain

Measurements of ozone concentrations, and meteorological and surface parameters were carried out over a flat green grassland in northwest Spain, in July 1995. Turbulent parameters and sensible and latent heat fluxes were calculated using the gradient technique. Fluxes and deposition velocity and resistances were evaluated assuming that the diffusivity for heat fluxes was equal to pollutant diffusivity. The daily average value of dry deposition velocity was 6 mm s-1 but it was influenced by wind velocity and atmospheric stability. Resistances have been calculated according to a simple resistance model and a comparison between theoretical and measured values has been made.

Ozone Dry Deposition in a Semi-Asanchezrid Steppe and in a Coniferous Forest in Southern Europe

Ozone dry deposition fluxes and velocities were measured in 1994 in a semi–arid steppe of central Spain and in a forest in southern France during the period of photochemical activity using the gradient method. Downward fluxes were systematically obtained in both sites, with lower values at nighttime and maximum values during the central period of the day, which showed the important role of stomata in ozone uptake. The range of deposition velocities was –0.005 to 1.160 in the forested site and 0.001 to 1.430 cm s–1 in the semi–arid steppe. The nocturnal deposition velocities observed in the semi–arid steppe were considerably higher than in the forest, with values up to 0.35 cm s–1. A single layer canopy model was applied and validated at both sites. The model fitted the daily patterns well but underestimated the observed values by 34% in the forest and by 10% in the semi–arid steppe. To improve the accuracy of the model, both soil and internal stomatal resistances, Rsoil and Ri, were estimated using a least square technique. The interdependence of both parameters and the relative humidity, rH, was evaluated through a statistical analysis of the residual between the observed deposition velocity and the aerodynamic, sub–layer, and stomatal resistances. The comparison between the parameter estimates under wet and dry conditions in both sites showed (1) the influence of rH on stomatal parameter and soil resistance, (2) the large contribution of stomatal conductance to ozone uptake during the daytime, and (3) the importance of soil as an additional pathway for ozone exchange, especially in the steppe. Taking into account the parameter estimates, the underestimate of the modeled results was 3% in the forest and 5% in the semi–arid steppe.

Dry deposition of ozone and sulphur dioxide over low vegetation in moderate southern European weather conditions. Measurements and modelling

Long-term measurements of SO 2 and O 3 dry deposition were carried out during one year over a grass field, located in the west coast of Portugal. An automatic system based on micrometeorological techniques provided, on a routine basis, an important data set for both gases. The results show strong daily and seasonal cycles in dry deposition velocity and surface resistance, for ozone, being also verified a seasonal trend for SO 2. For both gases maximum Rc values were observed in summertime with the minimum values occurring in winter and spring. These differences match with surface conditions. In Portugal the vegetation reaches its maximum of activity in spring and becomes partially dry in the end of summer, after several months without rainfall. The stomatal intake seems to be the most important controlling factor on dry deposition, specially for ozone. A parameterization of surface resistance for ozone based on conclusions from recent dry deposition studies yields Rc values in good agreement with the observed values. For SO 2, Rc values are influenced by other factors besides stoma opening such as surface wetness, being, therefore, more difficult to evaluate the applicability of existent parameterization schemes.