Long-range Transport Model Research Articles

Deposition of Ammonia Over an Eucalyptus globulus sp. Forest During Winter: Preliminary Results

Ammonia is a very important air pollutant, playing an widespread role in acid pollution chemistry. The knowledge of the deposition processes (wet and dry) is of extreme importance for both long-range transport modelling and evaluation of critical loads for specific ecosystems.Dry deposition fluxes of NH4+/NH3 over an Eucalyptus globulus sp young plantation were determined during winter in a coastal environment, using the micrometeorological gradient method. The atmospheric concentrations were measured using filter-pack samplers at four heights above the canopy, between 6 and 16 m from the ground. Vertical gradients of temperature and wind speed were also measured allowing for the calculation of aerodynamic resistances Parallel measurements of throughfall were made to estimate global deposition.This paper presents preliminary results of the deposition fluxes and highlights the need for further research in order to model deposition under the studied conditions.

Long-term trends in concentrations of halocarbons and radiatively active trace gases in atlantic and european air masses monitored at mace head, Ireland from 1987–1994

Long-term trends in trace gas concentrations over the period 1987–1994 are reported here for air masses advected to the Mace Head monitoring station on the remote west coast of Ireland. The trace gases covered include the principal halocarbons: CFC-11, CFC-12, CFC-113, CCl 4 and methyl chloroform; the radiatively active trace gases: carbon dioxide, methane, nitrous oxide and ozone; together with carbon monoxide, the major photochemical ozone precursor. By careful sorting using two independent techniques, it is possible to distinguish air masses that arrive at Mace Head from over the North Atlantic Ocean and those that have recently travelled over polluted European continental land areas. Concentration trends have been derived for each trace gas in polluted European continental and baseline North Atlantic maritime air and they appear to be distinctly different. Using a simple long-range transport model, estimates have been made of the European source strengths required to sustain the observed concentrations of each trace gas and their recent trends. These are compared with published emission inventories where they are available. The European continent appears to be a significant source of methane, carbon dioxide and nitrous oxide, a net sink for ozone and a declining source of the principal halocarbons and carbon monoxide.

A Model for Long-Range Transport of Desert Dust

An Eulerian model for dust transport in the atmosphere is designed, and a new parameterization scheme for dust uptake is developed. The model results are quantitatively compared with satellite observations for an intense dust transport event that occurred over the western Mediterranean in July 1985, showing a high degree of agreement.

The Danish Rimpuff and Eulerian accidental release model (the DREAM)

A combined tracer model, based on a Lagrangian meso-scale model and an Eulerian long-range transport model, for studying transport and dispersion of passive tracers caused by a single but strong source is presented. The combined model is briefly described and it is explained why it is worthwhile to apply a combination of two models in tracer simulations. A 3-dimensional version of the model is under development and some preliminary results from the first ETEX release will be shown. A short video has been made containing an animation of the development of the plumes from the Chernobyl accident and the two ETEX-releases.

Lateral Diffusion of Molecules Partitioned into Silica-Bound Alkyl Chains: Influence of Chain Length and Bonding Density

Lateral diffusion of a hydrophobic fluorescent molecule partitioned into monomeric alkyl chains bound to a planar silica substrate was measured as a function of chain density and chain length. Measurement of fluorescence recovery after patterned photobleaching was used to observe the diffusional relaxation of a concentration profile of probe molecules over distances of micrometers. The diffusion rate of the probe molecule partitioned into C-18 chains decreased with decreasing chain coverage. As the chain length was reduced from C-18 to C-8 and C-4, the rate of diffusion also decreased. These results, when combined with results from a previous study of the effect of overlaying solvent on diffusion rate (Hansen, R. L.; Harris, J. M. Anal. Chem. 1995, 67, 492-498), are consistent with a domain model for long-range transport of partitioned molecules through the bound ligands. Fluorescence recovery experiments in which diffusion is monitored over a distance of micrometers offer a unique means to probe long-range structure of surface-immobilized alkyl chains.

Mineral base-cation deposition in Asia

Efforts are being made to model the role of base-cation deposition due to wind-blown dust particles from arid and semi-arid regions in Central and Eastern Asia. In this paper, we estimate base-cation deposition in Asia on a one-degree spatial resolution in the region from Pakistan to Japan, and from Indonesia to Russia resulting from emissions from arid and semi-arid regions in China and Mongolia. Fluxes of base-cation rich soils into the atmosphere are estimated based on meteorological and land use information. The long-range transport and deposition of these particles are modeled using a multi-layer long-range transport model. Atmospheric concentrations and deposition fluxes (both wet and dry) of base-cation rich soils are estimated on a monthly basis for the springtime, when dust storms are most active. The calculated fluxes are compared to observations and are also used in estimations of acidic “Critical Loads” for Asia.

Wet deposition at the sub-20 km scale in a rural upland area of England

A network of 10 bulk precipitation collectors was established in an upland region of northern England to examine the small-scale variability of precipitation composition in a rural area. Significant spatial variability was shown for non sea-salt sulphate, calcium and hydrogen ion concentrations. Although nitrate concentrations did not show significant variability, a coherent gradient across the study area was observed. The large variability of calcium ion concentration across the area was related to limestone quarrying, which is prevalent in the south of the study area. Calcareous wind-blown soil may have also made a minor contribution to the abundance of calcium in the rain-water samples. It is likely, however, that a large fraction of the calcium was dry deposited to the funnels of the collectors in the form of particles. The network was not designed to study orographic enhancement of deposition, but it is suggested that this mechanism, along with wind-drift of scavenged cap-cloud droplets, cannot explain the spatial variation in ion concentrations. It is speculated that the variability in non-sea-salt sulphate concentrations may also be partially explained by reaction of CaCO 3 particles deposited to the funnels of the collectors with SO 2. Critical load exceedances in terms of deposited acidity from non-sea-salt sulphate were calculated using different spatially resolved deposition data. A better estimate of deposition in the study area was achieved by combining rainfall concentration data from the national network with the 5 km rainfall field, than the current methodology used for mapping of U.K. deposition which utilises a 20 km rainfall field. However, 20 km is considered to be the minimum resolution at which a procedure for parameterising orographic enhancement can be incorporated. Deposition and critical load exceedances in 2005 were calculated using a long-range transport model and significant improvements in the protection of soils were predicted from the projected emissions reductions.

A Lagrangian Model of Long-Range Transport of Sulphur with the Diurnal Variations of Some Model Parameters

Abstract A Lagrangian receptor-oriented one-layer model has been developed in order to simulate a synoptic-scale transport of airborne sulphur on a daily basis. Mass balance equations for sulphur dioxide and particulate sulphate were integrated along 3-day backward trajectories. Advective winds were determined from radiosonde reports, taking an average over the ground-based layer up to an 850-hPa level. The mixing height, transformation rate of sulphur dioxide to particulate sulphate, dry deposition velocities, and wet deposition rates for both pollutants were assumed to vary diurnally, depending on meteorological conditions. They were determined from routine synoptic observations. The model was tested for the sulphur dioxide and particulate sulphate data measured at nine and seven measuring sites, respectively. Daily mean calculated concentrations of both pollutants were generally higher than observed values for the test period. Both short- and long-term concentrations were predicted better for sulphur d...

An analysis of wet deposition of sulfate using a trajectory model for East Asia

A long-range transport model for East Asia was developed to estimate the wet deposition of sulfate. The model is a trajectory type which is appropriate for long-term analysis. Trajectories of air masses are calculated by tracing the wind field which changes spatially and temporally. The processes of reactions, rainout removal, intake of sulfate in cloud water into rain water, and dry and wet depositions are considered. It is possible to calculate the concentration of sulfate in precipitation at a receptor by performing material balance in a grid box containing the receptor. The results obtained by the long-range transport model were evaluated through comparison with observation data of acidic deposition. The observation was conducted at 21 stations throughout Japan for one year. The calculated amount of wet deposition of sulfate in Japan was 0.22Tg/y in S equivalent, while the observed amount was 0.29Tg/y. The long-range transport model can predict almost 80% of observed wet deposition. The contributions of domestic anthropogenic sources and volcanic eruption to wet deposition of sulfate in Japan were estimated using the longrange transport model. The ratio of the deposition of sulfate due to Japanese anthropogenic sources to that due to the Asian continental sources was about 1 to 2. Since air stream from the direction of the Asian continent dominates during winter, the contribution of Japan to wet deposition in the region which faces the Sea of Japan amounted to less than 15%. The contribution of the sulfur oxides from volcanoes was about 20%.

Development of hybrid LRT model to estimate sulfur deposition in Japan

We have developed a hybrid long-range transport (LRT) model to estimate long-term sulfur deposition amounts in Japan. This model combines a trajectory model for the LRT with an Eulerian model for the short-range transport and deposition. The hybrid model shows the ability to predict concentrations influenced by large nearby sources, which the trajectory model we previously developed consistently underestimated. The hybrid model is designed as an engineering model, which allows for long-term estimation without the requirements of detailed data on meteorology, surface condition, and emission over the whole domain, and huge computer resources required for comprehensive Eulerian models.

Energy use, emissions, and air pollution reduction strategies in Asia

In contrast to Europe and North America, air pollution in Asia is increasing rapidly, resulting in both local air quality problems and higher acidic depositions. In 1989, an east-west group of scientists initiated a multi-institutional research project on Acid Rain and Emissions Reduction in Asia, funded for the past two years by the World Bank and the Asian Development Bank. Phase I, covering 23 countries of Asia, focussed on the development of PC-based software called the Regional Air Pollution INformation and Simulation Model (RAINS-ASIA). A 94-region Regional Energy Scenario Generator was developed to create alternative energy/emission scenarios through the year 2020. A long-range atmospheric transport model was developed to calculate dispersion and deposition of sulfur, based upon emissions from area and large point sources, on a one-degree grid of Asia. The resulting impacts of acidic deposition on a variety of vegetation types were analyzed using the critical loads approach to test different emissions management strategies, including both energy conservation measures and sulfur abatement technologies.

A generalised description of the deposition of acidifying pollutants on a small scale in Europe

In describing the effects of acidification on the level of ecosystems, acid loads should be available at least on the size of ecosystems. No deposition maps on this resolution are available, hampering accurate estimation of exceedances of critical loads in Europe. Here, maps of small scale fluxes of Europe are presented. The maps are produced in close co-operation with EMEP. The acidifying components taken into account are oxidised sulphur and nitrogen and reduced nitrogen compounds. The method for estimating dry deposition is based on the combination of long-range transport model concentrations provided by EMEP and a detailed description of the dry deposition processes. Dry deposition velocities are calculated on a small scale using the inferential technique. Resistances are modelled using observations of meteorological parameters in Europe and parametrisation of surface exchange processes from deposition measurements. Wet deposition maps are derived using measured concentrations in precipitation in Europe together with precipitation amounts.

Measurements of atmospheric mercury concentrations in Northwestern and Central Europe — Comparison of experimental data and model results

Field experiments were carried out at various sites in Europe to compare ambient air and precipitation concentrations of atmospheric mercury with model data. In addition, ozone and aerosol black carbon concentrations in air were measured simultaneously as input data for validation of the EMEP-based European long-range transport model. Data sets for mercury in air and precipitation, ozone and aerosol black carbon show that the selected sites range from background conditions for Northwestern Europe to regionally influenced air masses from heavily industrialized Central Europe. Measured 12 h averaged mercury concentrations in air range from 2.1 ngm −3 for Mace Head, Ireland to 8.2 ngm −3 for the Halle/Leipzig/Bitterfeld area in former German Democratic Republic. Precipitation concentrations of total mercury from 17 to 460 ng l −1 were measured from 1991 to 1993 for the same sites. Experimental data and model results for total gaseous mercury and mercury in precipitation are in good agreement.

Estimating the emissions from a nuclear accident using observations of radioactivity with dispersion model products

The spread of material from fabricated nuclear releases simulated using the U.K. Met Office “NAME” long-range transport and dispersion model is used to test methods of modifying the modelled plume spread, and of assessing the release profiles, by comparing observed and modelled radioactivity. The method was also applied to reconstitute the first 108 h emissions from the Chernobyl incident. The results of the experiments were moderately encouraging.

Prediction of atmospheric sulphate deposition at sensitive receptors in northern India

Soil-derived particles in suspended particulate matter (SPM) are reported to be responsible for acid rain neutralization in India. A study on the seasonal variability of SPM indicates that the winter season SPM levels are significantly less than the summer season SPM levels thereby suggesting the winter season to be critical for acid rain. Therefore, SO 4 deposition is examined for the winter season at sensitive receptors in northern India using a long-range air transport model. The UW-LRT model is employed to estimate the SO 4 deposition levels at six locations given the point source emission quantities from 12 major sources. The model results match favourably with literature-reported deposition levels. The model results argue for a well-designed monitoring program for measurement of sulphate deposition to better determine the extent of the problem and model calibration.

A comparison of model and observed network estimates of sulphur deposition across Great Britain for 1990 and its likely source attribution

Long-range transport models for acidic sulphur species are being used to develop emission-control strategies to combat environmental acidification in the remote, sensitive regions of Europe. the incorporation of seeder-feeder enhancement into a simple trajectory model for sulphur has markedly improved the representation of wet deposition across Great Britain, as shown by a detailed comparison of the model results with the observations from monitoring networks. an uncertainty analysis reveals that those input parameters which contribute most to uncertainty in the total sulphur deposition are the sulphur-dioxide emissions, wind speeds and wet-removal coefficients. the total Great Britain dry and wet depositions of sulphur are estimated to be 216 and 241 thousand tonnes per year, respectively, making a total sulphur deposition per year of 457 ± 110 thousand tonnes, in excellent agreement with the observed quantity of 433 thousand tonnes. the model was used to give an indication of the origin of the deposited sulphur across Great Britain. European land-based sulphur sources contribute 34% of the deposition to Great Britain, with significant dry deposition in south-east England and wet deposition in upland western Britain. UK power stations and oil refineries contribute 46.7% of total deposition, with shipping and natural sulphur sources from algal blooms, a mere 4.6%. Differences in source attribution between this UK-scale study and those previously published for the long-range transport scale are explored and it is concluded that national-scale models have an important role to play in policy formulation.

Estimate of health impacts of acidifying air pollutants and tropospheric ozone in Europe

Based on combined information available from air quality monitoring data and long-range transport models, European population exposure to SO2, NO2 and O3 has been estimated. This information has been combined with the results of epidemiological studies assessing strength of association between the exposure and health effects to estimate an impact of the pollution on health in Europe. The analysis indicates that a considerable number of health problems, ranging from mild irritation of the respiratory system to increased mortality, can be attributed to short-term peaks of pollution observed in Europe. Chronic impacts of prolonged elevated SO2 levels on lung function are estimated to occur in close to10 million people in Europe.

Advances in receptor-oriented methodologies: a hybrid model for long-range transport of aerosol

Advances in receptor-oriented methodologies: a hybrid model for long-range transport of aerosol

Analysis of a regional model (EURAD) near surface gas concentration predictions using observations from networks

The three-dimensional long-range transport model EURAD has been applied to two episodes in 1986 to study the transport and transformation of air pollutants over Europe under different meteorological conditions. The spring episode is characterized by varying meteorological conditions over Europe and transport of pollutants is complex. The summer episode is suitable to study the enhanced formation of photooxidants as an almost stagnant high pressure system over central Europe favoured the accumulation of pollutants. Available observations from several monitoring networks in Europe are used to evaluate the near surface concentration predictions of the model. This is possible for the sulfur species, O3 and NO2 for the central part of the modelling domain. It is shown that O3 and NO2 trends in the western part of the model domain are estimated reasonably well. The strong bias for underpredicting NO2 in the eastern part of the domain reflects the quality of emission data for the two regions of the modelling area. Typically for regional scale Eulerian transport models when applied on larger grid sizes, EURAD overpredicts the observed minima and underpredicts the high observations. This is particularly true for O3 but also detectable in the sulfate comparisons. Several sensitivity simulations for both episodes were performed to test numerical algorithms, parameterizations or emission data. Results from these simulations clearly show the important role of cloud related processes during the spring time for the sulfur species. Further testing and assessment of cloud parameterizations and emission data for transport models is anticipated.

The modification of a semi-empirical long-range transport model to allow estimation of ambient sulfate concentrations

Abstract This paper describes the modification of a semi-empirical long-range transport model (STATMOD) to allow the estimation of ambient SO2 and sulfate concentrations, and sulfur concentrations in rain. These substances are relevant to the chemistry of deposition and the optical properties of aerosols. The improved model incorporates a treatment of SO2 oxidation to sulfate in non-precipitating clouds. Model parameters were determined by fitting model estimates of ambient SO2 and sulfate concentrations, and sulfate concentrations in rain, to corresponding observations from the Eulerian Model Evaluation and Field Study (EMEFS) and the National Dry Deposition Network (NDDN) databases for the period July-August-September 1988. The derived value of the parameter corresponding to the in-cloud conversion of SO2 suggests that sulfate formed in non-precipitating clouds made a substantial contribution to ambient sulfate concentrations belonging to the 1988 data set used in this study. To evaluate the general applicability of the parameter value, model estimates were compared with observations obtained from the Sulfate Regional Experiment (SURE), the Eastern Regional Air Quality Study (ERAQS), and the Acid Deposition System (ADS) databases for a similar time period in 1978. The results showed that the estimated concentrations were correlated with the observed concentrations of sulfur species for a similar period of a different year. This provides a test of the realism of the model as a first-cut engineering tool to examine the relationship between SO2 emissions and ambient sulfate levels.