Dry Deposition Model Research Articles

Dry Deposition in Urban Green Spaces: Insights from Beijing and Shanghai

Urbanization and industrialization have escalated air pollution into a critical global issue, particularly in urban areas. Urban green infrastructures (GIs), such as parks and street trees, play a vital role in mitigating air pollution through dry deposition, the process by which air pollutants are removed by deposition onto plant surfaces or through plant uptake. However, existing studies on the dry-deposition capacity of urban green spaces are limited in their ability to reflect variations at the tree-species level, hindering comprehensive evaluations and effective management strategies. This study aims to quantitatively assess the dry-deposition capacity of the urban green spaces of Beijing and Shanghai for six major air pollutants in using an improved dry-deposition model and tree-species-specific data. Results showed that Shanghai’s urban green spaces had a monthly average dry-deposition rate of 5.5 × 10−6 s m−1, slightly higher than Beijing’s rate of 5.3 × 10−6 s m−1. Significant seasonal variations were observed, with summer showing the highest deposition rates due to favorable meteorological conditions. Broad-leaved species such as Zelkova serrata in Beijing and Photinia serratifolia in Shanghai exhibited superior dry-deposition capacities compared to coniferous species. Temperature significantly influenced dry-deposition rates for gaseous pollutants, while particulate-matter deposition was primarily affected by pollutant concentrations. This study provides critical insights into the air = purification functions of urban green spaces and underscores the importance of species selection and strategic green-space planning in urban air-quality management, informing the development of optimized urban-greening strategies for improved air quality and public health.

An Assessment Framework for Mapping the Air Purification Service of Vegetation at the Regional Scale

Efficiently mitigating the severe air pollution resulting from rapid progress is crucial for the sustainable development of the socio-ecological system. Recently, concerns about nature-based solutions have emerged in the research on the treatment of air pollution. Studies on the purification of PM2.5 using vegetation currently concentrate on the individual scale of tree species or urban vegetation, ignoring the regional scale, which could better assist ecological governance. Therefore, taking the Fenwei Plain of China as the study area, an assessment framework of the air purification service’s spatial distribution reflecting regional vegetation was constructed. The dry deposition model and GeoDetector were used to quantify the spatial-temporal pattern and explore natural driving factors on the removal of PM2.5. The results showed that (1) the PM2.5 purification services offered by various types of vegetation exhibit notable variations. The average removal rates of PM2.5 by vegetation were 0.186%, 0.243%, and 0.435% in 2000, 2010, and 2021, respectively. (2) Meanwhile, a wide range of spatial mismatch exists between the PM2.5 concentration and PM2.5 removal. Insufficient supply regions of PM2.5 purification services account for 50% of the Fenwei Plain. (3) PM2.5 removal was strongly influenced by the types of vegetation and the Normalized Vegetation Index (NDVI), followed by the Digital Elevation Model (DEM), and less affected by meteorological factors; a strong joint effect was shown among the factors. The findings in this research provide a new perspective on regional air pollution management at the regional scale.

A new dry deposition model implemented in CALPUFF code to simulate contamination of radionuclides released into atmospheric environment post-nuclear accidental event

Long-range transport and deposition analyses of 137Cs following a hypothetical incident at Gösgen nuclear power plant are studied by using CALMET-CALPUFF model system. Comparisons are performed with results obtained from a version modified of CALPUFF using a new dry deposition velocity model. This model is based on a combination of aerodynamic resistances and considers local features of the mutual influence of inertial impact and turbulent processes. The results show that the modified CALPUFF code seems to be an appropriate tool for performing impact assessments on long-range transport in complex terrain contexts or to support preparedness and response capabilities for nuclear and radiological accidents.

Revisiting dry deposition modelling of particulate matter on vegetation at the microscale

Revisiting dry deposition modelling of particulate matter on vegetation at the microscale

Atmospheric particulate matter retention capacity of bark and leaves of urban tree species

Urban vegetation can effectively filter and adsorb particulate matter (PM). However, limited studies have been conducted on the PM retention capacity of tree barks. This study investigated the ability of five common urban tree species in the Yangtze River Delta region to retain PM through their barks and leaves by conducting a 14-day tree PM retention experiment on the five tree species during autumn and winter. The results showed that (1) the PM retention per unit area of bark was 6.9 times and 11.8 times higher than that of leaves during autumn and winter, respectively; (2) when considering total surface area, bark and leaves exhibited comparable PM retention capacities at the whole-plant scale; (3) the ability of bark to retain PM is species-specific, which can be attributed to different bark morphology among different tree species; and (4) bark and leaves exhibited distinct preferences for retaining PM of different particle sizes, even when exposed to similar environmental conditions. This study highlights the remarkable ability of tree bark to PM removal and provides valuable insights into the role of urban trees in mitigating PM pollution. Furthermore, these findings can provide valuable insights into studies on dry deposition modelling, urban planning, and green space management strategies.

Ozone Fluxes Over a Boreal Lake Exhibit Enhanced Deposition at Nights

AbstractA few studies on ozone deposition over lake water are available and so far only one using the eddy covariance technique (Wesely et al., 1981, https://doi.org/10.1007/BF00122295). A 23‐day field campaign was held in August‐September 2012 at the Lake Kuivajärvi in Hyytiälä, Finland. The results showed a mean flux of −30 ± 1 ng m−2 s−1 and deposition velocity of 0.86 ± 0.05 mm s−1. Deposition velocity showed a weak diurnal cycle over the lake with elevated values during the nighttime. The daytime and nighttime portions of the data set differed statistically. Analysis showed that waterside convective mixing enhanced deposition and such conditions pre‐dominantly occurred during nighttime. We compared the measured deposition velocities with the dry deposition model of air‐sea exchange, adjusted for the chemical sinks relevant for the lake. We suggest that the buoyant mixing and unaccounted chemistry can be responsible for the difference between the model results and observations.

A database of atmospheric inorganic nitrogen deposition fluxes in China from satellite monitoring

Over the past century, atmospheric inorganic nitrogen (IN) deposition to terrestrial ecosystems has significantly increased and caused various environmental issues. China has been one of the hotspot regions for IN deposition, yet limited data exist regarding IN deposition fluxes in China at the regional scale. In this study, based on NO2 and NH3 columns acquired by satellite sensors, coupled with atmospheric chemical transport model (CTM), mixed-effects model and site observations, we constructed regional-scale IN dry and wet deposition models respectively, and finally proposed a spatially explicit database of IN deposition fluxes in China. The database includes the dry, wet and total deposition fluxes in China during 2011–2020, and the data are presented in raster form with a resolution of 0.25° × 0.25°. Overall, the database is of great importance for monitoring and simulating the trends of IN deposition over a long time series in China.

Quantitative estimation of the PM2.5 removal capacity and influencing factors of urban green infrastructure

Long-term exposure to PM2.5 (fine particulate matter with an aerodynamic diameter <2.5 μm) could cause great harm to human health and sustainable development. It remains a challenge to estimate the long-term PM2.5 removal capacity of nature-based green infrastructure in urban areas. In this paper, the annual PM2.5 removal capacity of urban green infrastructure (UGI) from 2000 to 2019 in Shenyang was estimated based on the PM2.5 dry deposition model. The spatial heterogeneity of annual PM2.5 removal capacity were detected Sen-MK test and local spatial autocorrelations analysis. Then the effects of landscape patterns and socioeconomic variables on PM2.5 removal capacity were explored based on linear regression model. The results illustrated that the PM2.5 removal capacity of UGI increased significantly from 2000 to 2019 in Shenyang, with the amount of PM2.5 removal, PM2.5 removal flux and removal rate increasing by 20.64 Mg/a, 0.0258 g/m2/a, and 0.377 %/a, respectively. The PM2.5 removal capacity of UGI exhibited spatial heterogeneity in the study area. Specifically, the regions experiencing the increase in PM2.5 removal capacity of UGI accounted for majority of the old urban area of Shenyang City during the study period; the lower PM2.5 removal capacity clustered in the center urban area, in which high density impervious surfaces distributed, while the higher PM2.5 removal capacity mainly gathered in the area with large scale green space; PM2.5 removal capacity were significantly higher in urban functional zones with a high proportion of green spaces. The landscape metrics representing fragmentation and shape complexity positively affected the annual PM2.5 removal flux and removal rate, while the aggregation metrics had significantly negative correlations with the PM2.5 removal flux and removal rate. Moreover, it was also found that population density and GDP negatively affected the PM2.5 removal capacity of UGI. This study provides a methodological reference and some new insights for future urban landscape planning and air pollution purification.

Application of the COCOSYS code in the safety evaluation of Czech nuclear power plants

Abstract Safety analyses of nuclear power plant accidents are a key tool in demonstration of nuclear safety and reliability. The chain of the safety analyses comprises several follow-up activities like neutronic core calculation, primary system simulation and containment response to a loss-of-coolant accident. The analyses can be done with numerous computational tools like the GRS codes ATHLET and COCOSYS. The COCOSYS and its predecessor RALOC have been used in a variety of safety analyses at UJV conducted in the framework of technical support of the Czech nuclear power plants. Application of the code in the field of nuclear power plant safety analyses is ruled by the Czech legislative, which defines a process called standardization. The standardization procedure equivalent to validation and verification process provides further independent validation on the level of user organization. In past decades, COCOSYS has been successfully used in numerous DBA and DEC-A analyses of VVER-1000/V-320 containment, evaluating both thermal hydraulic conditions as well as fission product source term. This paper summarizes independent COCOSYS validation at UJV, including setup of the iodine dry paint deposition model to Ameron Amerlock paint. Furthermore, a VVER-1000/V-320 containment model is presented and analysis of DBA and DEC-A LB LOCA at VVER-1000/V-320 is conducted. The evaluation of the results aims at confirmation of acceptance criteria related to containment and impact of containment spray system. An emphasis is given to evaluation of containment source term, where comparison of both events is conducted for release of iodine, cesium, and xenon.

Dry Deposition Methods Based on Turbulence Kinetic Energy: Part 1. Evaluation of Various Resistances and Sensitivity Studies Using a Single-Point Model.

Different functions are used to account for turbulence strength in the atmospheric boundary layer for different stability regimes. These functions are one of the sources for differences among different atmospheric models' predictions and associated biases. Also, turbulence strength is underrepresented in some of the resistance formulations. To address these issues with dry deposition, firstly we take advantage of three-dimensional (3-D) turbulence information in estimating resistances by proposing and validating a 3-D turbulence velocity scale that is relevant for different stability regimes of boundary layer. Secondly, we hypothesize and validate that friction velocity measured by 3-D sonic anemometer can be effectively replaced by the new turbulence velocity scale multiplied by the von Karman constant. Finally, we (1) present a set of resistance formulations for ozone (O3) based on the 3-D turbulence velocity scale; (2) intercompare estimations of such resistances with those obtained using existing formulations; and, (3) evaluate simulated O3 fluxes using a single-point dry deposition model against long-term observations of O3 fluxes at the Harvard Forest (MA) site. Results indicate that the new resistance formulations work very well in simulating surface latent heat and O3 fluxes when compared to respective existing formulations and measurements at a decadal time scale. Findings from this research may help to improve the capability of dry deposition schemes for better estimation of dry deposition fluxes and create opportunities for the development of a community dry deposition model for use in regional/global air quality models.

A New Aerosol Dry Deposition Model for Air Quality and Climate Modeling

AbstractDry deposition of aerosols from the atmosphere is an important but poorly understood and inadequately modeled process in atmospheric systems for climate and air quality. Comparisons of currently used aerosol dry deposition models to a compendia of published field measurement studies in various landscapes show very poor agreement over a wide range of particle sizes. In this study, we develop and test a new aerosol dry deposition model that is a modification of the current model in the Community Multiscale Air Quality (CMAQ) model. The new model agrees much better with measured dry deposition velocities across particle sizes. The key innovation is the addition of a second inertial impaction term for microscale obstacles such as leaf hairs, microscale ridges, and needleleaf edge effects. The most significant effect of the new model is to increase the mass dry deposition of the accumulation mode aerosols in CMAQ. Accumulation mode mass dry deposition velocities increase by almost an order of magnitude in forested areas with lesser increases for shorter vegetation. Peak PM2.5 concentrations are reduced in some forested areas by up to 40% in CMAQ simulations. Over the continuous United States, the new model reduced PM2.5 by an average of 16% for July 2018 at the Air Quality System monitoring sites. For summer 2018 simulations, bias and error of PM2.5 concentrations are significantly reduced, especially in forested areas.

Nocturnal pollutant uptake contributes significantly to the total stomatal uptake of Mangifera indica

DO3SE (Deposition of Ozone for Stomatal Exchange), is a dry deposition model, designed to assess tropospheric ozone risk to vegetation, and is based on two alternative algorithms to estimate stomatal conductance: multiplicative and photosynthetic. The multiplicative model has been argued to perform better for leaf-level and regional-level application. In this study, we demonstrate that the photosynthetic model is superior to the multiplicative model even for leaf-level studies using measurements performed on Mangifera indica. We find that the multiplicative model overestimates the daytime stomatal conductance, when compared with measured stomatal conductance and prescribes zero conductance at night while measurements show an average conductance of 100 mmol(H2O)m−2s−1 between 9 p.m. and 4 a.m. The daytime overestimation of the multiplicative model can be significantly reduced when the model is modified to include a response function for ozone-induced stomatal closure. However, nighttime pollutant uptake fluxes can only be accurately assessed with the photosynthetic model which includes the stomatal opening at night during respiration and is capable of reproducing the measured nighttime stomatal conductance. At our site, the nocturnal flux contributes 64%, 39%, 46%, and 88% of the total for NO2 uptake in winter, summer, monsoon, and post-monsoon, respectively. For SO2, nocturnal uptake amounts to 35%, 28%, 28%, and 44% in winter, summer, monsoon, and post-monsoon, respectively while for ozone the nighttime uptake contributes 30%, 17%, 18%, and 29% of the total stomatal uptake in winter, summer, monsoon, and post-monsoon respectively.

High-resolution spatial analysis for the air quality regulation service from urban vegetation: A case study of Taipei City

Rapid economic growth has caused air pollution, particularly in city areas. Removing air pollutants generated by various emission sources is crucial to control PM2.5, improve air quality, and maintain human health in high-density urban areas. In response to air pollution, urban vegetation plays an essential role in providing air quality regulation service. To estimate the air quality regulation service provided by urban vegetation, this study integrated spatial analysis, a dry deposition model, and an atmospheric diffusion model to spatially quantify the air quality regulation service of PM2.5 in Taipei City on a high-resolution scale (30 m × 30 m per spatial unit). The results show that in 2016, total PM2.5 emissions in Taipei City were 1,400.88 tonnes and that urban vegetation removed 18.31 tonnes of PM2.5, with an average PM2.5 removal rate of 0.16 g/m2, and the corresponding PM2.5 concentration improvement value of 0.0136 μg/m3. This finding revealed a significant gap between the amounts of emissions and purifications of PM2.5, the air quality regulation service provided by the urban vegetation in Taipei City remains insufficient. The results of this study not only point out the spatial differences of regulation services and propose a new research framework for quantifying the natural benefits, but also as a guideline for governments to form the auxiliary policies of the urban ecosystem service and facilitate the urban green infrastructure planning.

A Simple Parameterization to Enhance the Computational Time in the Three Layer Dry Deposition Model for Smooth Surfaces

Optimization of dry deposition velocity calculation has been of great interest. Every time, determining the value of the concentration boundary layer (CBL) thickness led to a waste of numerical calculation time, which appears as a huge time in large-scale climate models. The goal of this study is to optimize the numerical calculation time in the three-layer deposition model for smooth surfaces through the development of a MATLAB code that can parameterize the appropriate concentration boundary layer height (y+cbl) and internal integral calculation intervals for each particle diameter Dp (0.01–100 µm) and friction velocity u* (0.01–100 m/s). The particle concentration, as a solution to the particle flux equation, is obtained and modeled numerically by performing the left Riemann sum using MATLAB software. On the other hand, the number of subdivisions N of the Riemann sum was also parameterized for each Dp and u* in order to lessen the numerical calculation time. From a numerical point of view, the new parameterizations were tested by several computers; about 78% on the average of the computation time was saved when compared with the original algorithm. In other words, on average, about 1.2 s/calculation was gained, which is valuable in climate models simulations when millions of dry deposition calculations are needed.

Influence of plant ecophysiology on ozone dry deposition: comparing between multiplicative and photosynthesis-based dry deposition schemes and their responses to rising CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; level

Abstract. Dry deposition is a key process for surface ozone (O3) removal. Stomatal uptake is a major component of O3 dry deposition, which is parameterized differently in current land surface models and chemical transport models. We developed and used a standalone terrestrial biosphere model, driven by a unified set of prescribed meteorology, to evaluate two widely used dry deposition modeling frameworks, Wesely (1989) and Zhang et al. (2003), with different configurations of stomatal resistance: (1) the default multiplicative method in the Wesely scheme (W89) and Zhang et al. (2003) scheme (Z03), (2) the traditional photosynthesis-based Farquhar–Ball–Berry (FBB) stomatal algorithm, and (3) the Medlyn stomatal algorithm (MED) based on optimization theory. We found that using the FBB stomatal approach that captures ecophysiological responses to environmental factors, especially to water stress, can generally improve the simulated dry deposition velocities compared with multiplicative schemes. The MED stomatal approach produces higher stomatal conductance than FBB and is likely to overestimate dry deposition velocities for major vegetation types, but its performance is greatly improved when spatially varying slope parameters based on annual mean precipitation are used. Large discrepancies were also found in stomatal responses to rising CO2 levels from 390 to 550 ppm: the multiplicative stomatal method with an empirical CO2 response function produces reduction (−35 %) in global stomatal conductance on average much larger than that with the photosynthesis-based stomatal method (−14 %–19 %). Our results show the potential biases in O3 sink caused by errors in model structure especially in the Wesely dry deposition scheme and the importance of using photosynthesis-based representation of stomatal resistance in dry deposition schemes under a changing climate and rising CO2 concentration.

Towards an experimental approach for measuring the removal of urban air pollutants by green roofs

Green roofs are a promising approach to mitigate air pollution in urban environments, but limited experimental data is yet available. In this study, we developed a laboratory-scale setup to measure the removal nitrogen dioxide (NO2) and ozone (O3) using a variety of common green roof species. Experiments were conducted on detached leaves and whole plants using two chambers (0.6 L and 12 L), visible lighting, NOx/O3 sources and online analyzers. Three species were the best performant (Thymus vulgaris, Sedum sexangulare and Heuchera Americana L.) with deposition velocities (vd) ranging from 1.6 to 4.82 m/h for NO2, and 1.7–5.56 m/h for O3. In both cases, thyme was the most effective plant likely due to its higher stomatal area and the reactivity of its volatile metabolites with O3 leading to several oxidized by-products. Furthermore, NO2 uptake was found to be enhanced by surface water released by leaf transpiration leading to the production of nitrous acid (HONO). Similar values of (vd) were observed (3.84–4.65 m/h) when whole thyme plant was used. The soil was also found to be competitive in removing O3 but less performant in capturing NO2. Using a dry deposition model, we estimated that the three plant species can uptake up to 9 kg/ha/year of NO2 and 13.6 kg/ha/year, which fall in agreement with previously reported modeling data. Our experimental approach can be a rapid tool for screening the depollution performances of green roof species enabling an effective prioritization for deployment in urban environments.

Dry deposition of particulate matter and its associated soluble ions on five broadleaved species in Taichung, central Taiwan

Many studies have estimated particulate matter (PM) removal by urban trees using dry deposition models; however, few studies have quantified the accuracy of their results. Thus, this study investigated the dry deposition of PM and its associated soluble ions in five broadleaved species in three districts of Taichung, central Taiwan, through field experiments. The total suspended particulate (TSP) dry deposition flux on leaf surfaces varied with sampling time, site, and tree species. By contrast, single-factor effects were observed for PM10 and PM2.5. The average dry deposition velocities of TSPs, PM10, and PM2.5 were 0.63, 0.062, and 0.028 cm s−1, respectively. Moreover, the dry deposition velocities of sulfate and nitrate were estimated to be 0.186 and 0.194 cm s−1, respectively. A significant relationship was observed between the ambient concentration and the dry deposition flux for all size fractions of PM. By contrast, weak and negative correlations were found between particle deposition velocity and wind speed. The measured PM2.5 dry deposition velocity was approximately equal to the dry deposition velocity obtained with the i-Tree model (0.03 cm s−1), which indicated the promising application potential of i-Tree in Taiwan. Compound and rough leaves, such as leaves of the Taiwan golden-rain tree, intercepted a high amount of PM2.5, whereas the pongam tree, which has thin leaves and wax surfaces, exhibited the lowest TSP interception. Species difference mostly occurred in the dry deposition flux of nitrate rather than sulfate; however, the interception of sulfate by trees revealed the possibility of the long-range transport of air pollutants. The results of this study elucidate the dry deposition of PM and its associated soluble ions in real-world situations.

Volatility Dependence of the Aerosol Size Distributions of Nonpolar Organic Compounds: A Case Study in Shanghai

AbstractThe aerosol size distribution of organic compounds is one of the fundamental characteristics that regulates their atmospheric deposition and environmental fate. In this study, we characterized the organic components (mostly nonpolar organic compounds) in size‐resolved particles, with a focus on polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (O‐PAHs), n‐alkanes, and polybrominated diphenyl ethers (PBDEs), in the urban Shanghai atmosphere during a 1‐year sampling period using gas chromatography (GC) coupled to tandem mass spectrometry (GC‐MS/MS) and two‐dimensional GC with a flame ionization detector (GC × GC‐FID). These compounds ranged from volatile organic compounds (VOCs) to extremely low volatility organic compounds (ELVOCs). We related their aerosol size distributions with their volatilities. On average, high positive correlations (p &lt; 0.01) were observed between the size distribution characteristics (e.g., geometric mean diameter [GMD] and mass fraction in coarse particles) and volatility (logarithmic value of the saturation mass concentration, log C*) for the compounds that we examined. A higher ambient temperature tends to increase the slope of the regression line between size distribution and volatility (log C*). Further dry deposition modeling of size‐resolved particles showed a positive correlation (p &lt; 0.01) between the bulk dry deposition velocity and GMD and between the bulk dry deposition velocity and volatility of the target compounds, indicating that low‐volatility organic compounds have a lower dry deposition velocity and are more likely to be transported to remote areas if they do not have a short half‐life in the atmosphere.

Comprehensive Modeling of Dust Accumulation on PV Modules Through Dry Deposition Processes

Solar photovoltaic (SPV) array does not give constant power output due to the adverse effects of various stresses over its performance. Dust is a critical affecting factor, especially in tropical, arid, and semiarid regions, as it reduces power output by lowering the transmittance of the glass cover. Usually, total dust accumulation on an SPV module goes through three processes viz., deposition, rebound, and re-suspension. In this article, a detailed analysis of all these phenomena has been carried out to build up a comprehensive model for dry deposition of dust to assess power output reduction for this. Variations of all these processes for particles with different diameters and modules at various tilt angles have also been investigated. The model shows that transmittance becomes minimum at a tilt angle of about 15°, which is validated by laboratory experimentation. The deviation between measured and the model-based calculated dust deposition density is found to be 4.84%. The energy output of 10 kWP PV power plant has been calculated with this model with weather data collected from a weather monitoring station (at latitude 22.5713°N, longitude 88.3109°E) and dust data from a website of Government of India. Daily generated energy in this plant for 15 days is recorded by a digital meter and compared with the calculated ones. The deviation between the two is seen to be within ±6%.

Measurement and modelling of gaseous elemental iodine (I2) dry deposition velocity on grass in the environment

Assessing the impact of radioactive iodine on humans subsequent to a nuclear accident requires a better understanding of its behaviour in the environment. An original approach aimed at developing a model constrained by data collected during experimental campaigns has been developed. These experimental campaigns, named MIOSEC 2 and MIOSEC 3 respectively, were conducted in the middle of grassland. They are based on emissions of gaseous elemental iodine (I2) into the atmosphere above the grassland to determine the dry deposition velocities of iodine on the grass and to model these velocities as a function of the environmental conditions, particularly wind friction velocity, sensible heat flux, and stomatal resistance. The measured dry deposition velocities were between 0.02 and 0.49 cm s−1 during MIOSEC 2, varying by more than one order of magnitude, and between 0.48 and 1.25 cm s−1 during MIOSEC 3. The dry deposition model for iodine developed as a result of these experiments relies on the micrometeorological characteristics of the atmospheric surface layer, the pertinent physical and chemical properties of the iodine and the surface properties of the grass; all these parameters were measured at the time of the experiments. Given the experimental conditions, the modelled dry deposition velocities varied between 0.11 and 0.51 cm s−1 during MIOSEC 2 and between 0.31 and 1.6 cm s−1 during MIOSEC 3. The dry deposition model for iodine indicates that the variations in deposition velocity are induced by the mechanical turbulence, since there is significant correlation between the dry deposition velocities of iodine and the wind friction velocities on grass. The model also shows that the higher deposition velocity values during MIOSEC 3 are due to the fact that the stomata were more open during the experiments. There is also significant correlation between the experimental results and modelled values both for MIOSEC 2 (R2 = 0.61) and for MIOSEC 3 (R2 = 0.71).