Acid Deposition And Oxidant Model Research Articles

A comprehensive Eulerian modelling framework for airborne mercury species: model development and applications in Europe

A comprehensive mercury model system using the Eulerian reference frame of the Acid Deposition and Oxidant Model (ADOM) has been developed under the Canada–Germany Science & Technology Co-operation Agreement and applied within the European Union MArine Science and Technology–BAltic Sea SYstem Study (MAST-III-BASYS) and the Environment & Climate project Mercury Species over Europe (MOE), to study the regional transport and deposition fluxes of atmospheric mercury species. The model is able to simulate long-range transport of mercury over the entire depth of the troposphere with a basic time step of 1 h and incorporates current knowledge of physico-chemical forms and transformation reactions of atmospheric mercury species. Model predicted concentration and deposition pattern of mercury species over Europe are presented and concentrations of total gaseous mercury in ambient air and total mercury in precipitation calculated by the model are compared with observed values from a BASYS monitoring network study in February/March 1998. Concentrations in air agree within a factor of about 2 with observed values, thus indicating that the model is capable of reproducing observations satisfactorily even on an hourly basis. Observed monthly average concentrations in precipitation at four monitoring stations at the Baltic Sea coast are reproduced by the model within a factor of 1.3 suggesting that the chemical scheme in the model is based on an adequate parameterisation of aqueous phase chemistry.

Studying ozone climatology with a regional climate model: 1. Model description and evaluation

On the basis of the Canadian Regional Climate Model (CRCM) a new regional oxidant model has been developed to study ozone climatology in eastern Canada. In addition to the semi‐Lagrangian advection and vertical diffusion schemes already present for tracers, a chemical module, dry deposition parameterization, and anthropogenic and on‐line biogenic emissions were added to the CRCM. The complete model forms a single system which integrates meteorological and chemical variables simultaneously. Transport of 25 chemical species is evaluated on a 80 × 80 horizontal grid at 42.3 km resolution and for the 24 unequally spaced levels. The chemical scheme includes 47 species and 114 reactions used in the Acid Deposition and Oxidant Model (ADOM) gas‐phase mechanism. Precalculated photolysis rates, corrected for the model cloud cover through the variations of the simulated solar radiation penetration, are used in the model. This limited‐area model is driven at its boundaries by objective reanalyses for the meteorological fields and by climatological concentrations for the chemical counterparts. A time step of 15 min common to all processes is currently used. A two‐step validation procedure, which includes specific cases and climatological simulations, was adopted. The first test consists of a week‐long simulation for the first week of August 1988 when an intense ozone episode affected most of northeastern America during the first Eulerian Model Evaluation and Field Study (EMEFS) campaign. Results show that the CRCM ability to simulate this episode is comparable to other existing models using off‐line approaches. The CRCM performance was substantially improved by the addition of the biogenic emission parameterization. Climatology‐specific results are presented in the companion paper by Bouchet et al. [this issue].

A comprehensive Eulerian modeling framework for airborne mercury species: Development and testing of the Tropospheric Chemistry module (TCM)

A comprehensive mercury model system using the Eulerian reference frame of the Acid Deposition and Oxidant Model (ADOM) is being developed to study the regional transport of atmospheric mercury species. A stand-alone version of the ADOM cloud mixing, scavenging, chemistry and wet deposition model components referred to as the Tropospheric Chemistry Module (TCM) is used to investigate the sensitivity of various chemical and meteorological parameters, assumed to be important for mercury deposition phenomena. The TCM chemistry scheme was developed by systematic simplification of the detailed Chemistry of Atmospheric Mercury (CAM) process model, which is based on the current knowledge of physico-chemical forms and transformation reactions of atmospheric mercury species. The first part of the paper describes the general approach to the TCM formulation. The second part presents sensitivity studies of the TCM behavior under different environmental conditions and a comparison of TCM results with observed concentrations of total mercury concentrations in precipitation (Hg(tot)). The results indicate that the TCM has capabilities to examine the relative importance and sensitivity of numerous mercury processes in the troposphere and to reproduce observed Hg(tot) concentrations reasonably well justifying its ultimate use in the full ADOM model.

The influence of the dry deposition on the lead concentration in aerosols dependent on the particle size over the Baltic Sea

In recent studies concerning modelling aerosol transport and deposition over Europe widely emission estimates of heavy metals, associated with particles, integrated over the size distribution have been used. This is a crucial simplification of the real conditions and reflects an important weakness of the emission inventories. Also the dry deposition parameterization often performed by a single value of the dry deposition velocity representative for mean particle-size distributions can be expected to be rather uncertain. The results of many investigations which provide estimates of atmospheric depositions are based on such assumptions. However compared to the emissions about the dry deposition process there is a much better knowledge which can be used for modelling. The idea in this study was to combine the best available information about particle size dependent emissions and a dry deposition scheme applicable for different particle sizes. The motivation was the evaluation of impactor measurements of particle size segregated lead concentrations in aerosols at the coast of the Baltic Sea. In order to determine the dry deposition over the Baltic Sea the deposition module of the ADOM model was adapted for different sizes of lead containing particles. The model referred to as ADOM (Acid Deposition and Oxidant Model) originally has been developed under the sponsorship of Environment Canada, Atmospheric Environment Service(AES), the Ontario Ministry of Environment and Energy (OMEE), the German Umweltbundesamt and the Electric Power Research Institute (EPRI) for simulating long-range transport and deposition of acidic pollutants in Europe and North America (Venkatram et al., 1988). Presently it is modifyed for heavy metals (Krüger and Petersen, 1996). The dry deposition module of ADOM is formulated by means of an electrical resistance analog. The basis for the electrical analog is the Ohm's law which relates voltage to resistance and current. In the analogous relation for the dry deposition the concentration is analogous to voltage the flux is analogous to current and the inverse of the deposition velocity is analogous to total resistance. For the estimation of the flux the pollutant transfer is thought to occur in the constant flux layer and the deposition layer. In the dry deposition scheme small particles (diameter < 0.05μm) within the deposition layer are transported much in the same way like gases. The Brownian diffusion is considered as the primary transport mechanism. The deposition of larger particles is parameterized by the settling velocity and the stopping time, which are dependent on the Stokes number and collection efficiencies. The roughness lengths of 12 land use categories identical with those of the PHOXA land use data base for Europe are taken into account.The ADOM dry deposition module was applied to air mass movements over the Baltic Sea. Typical trajectories for the receptor point Kap Arkona located in the North East of Germany were investigated. As initial concentrations emission data for lead which are documented in van den Hout, K.D. (1994) were used for the calculations. This inventory contains a general separation of the aerosol size distribution into the 5 diameter intervals (<0.95μm, 0.95–4μm, 4–10μm, 10–20μm, >20μm). The meteorological data along the trajectories were taken from the HIRLAM weather forecast model (Källen, 1996). The dry deposition was calculated along air mass back trajectories for the receptor point Kap Arkona. The results indicate that there is a pronounced decrease of the initial concentration during the first hours of transport. Consequently after some hour simulation time the lead is only concentrated in aerosols of diameters lower than 4μm (figure 1). These findings are quite different compared to the lead concentrations found in size distributions measured at Kap Arkona. The present interpretation of the investigations is that interactions of aerosol particles of different sizes seem to have a strong influence. Possibly particles from sea spray play an important role during the transport over the sea.▪

Vertical profiles of ozone during the EMEFS I experiment in Southern Ontario

Vertical profiles of ozone from the surface to over 15 km altitude were obtained with a combination of free-flying and tethered ozonesondes and differential absorption lidar. During the Eulerian Model Evaluation Field Study (EMEFS I) of July–August 1988, these profiles were compared with the output of a sophisticated regional-scale three-dimensional Eulerian dispersion and chemistry model, the Acid Deposition and Oxidant Model (ADOM). The results show that ADOM predicts the ozone concentration profiles with accuracy only in the lower troposphere and particularly well during simple synoptic situations. In the upper troposphere, the model does not predict the intrusions of ozone from the stratosphere which appear to be extremely important in determining the ozone concentration profile.

An evaluation of the ADOM cloud module

Abstract The Acid Deposition and Oxidant Model (ADOM) is an Eulerian long‐range transport and deposition model. One of the most highly parametrized and least well established parts of the model is the scavenging module that describes cloud formation, pollutant scavenging, aqueous‐phase chemistry and wet deposition. As a means of gaining insight into the scavenging module, results from simulations with the module are compared with the results from simulations for equivalent conditions with a three‐dimensional dynamic cloud chemistry model. Comparisons of results for a variety of initial conditions show that wet deposition of sulphate, nitrate and ammonium ions tend to be underpredicted by the scavenging module and that the pH of the rain is overpredicted. Although the differences are for the most part not large, they are sensitive to cloud top height. The amount of hydrogen peroxide deposited at the surface is significantly smaller in the ADOM module than in the cloud chemistry model. For the particular co...

Evaluation of a comprehensive Eulerian air quality model with multiple chemical species measurements using principal component analysis

Using a principal component analysis technique and data on atmospheric gases and aerosols at a rural site in Ontario, Canada from the Eulerian model evaluation field study (EMEFS), the Eulerian acid deposition and oxidant model (ADOM) is evaluated. Seventy-nine and 76% of the variances in the data and model output, respectively, are explained by three principal components. They are a chemically aged/ transported component, a diurnal cycle component, and an area emission component, all characterized by their ratios of gases and temporal variation patterns. The ADOM component contributions to sulphur species are in general agreement with the EMEFS components, but with notable differences for key photochemical species including O 3. The temporal variations of the ADOM components are close to those of the EMEFS components. The EMEFS chemically aged/transported component shows a high degree of photochemical processing, with the ratios [NO x ]/[TNO y ]=0.3 and [O 3]/([TNO y ]−[NO x ])=9±1. The corresponding ADOM component predicts lower G[NO x ]/[TNO y ] and [NO 3]/([TNO y ]−[NO x ]) ratios, probably caused by a chemical mechanism in the model that is too fast, and lower contributions to O 3, NO 2, TNO 3, PAN, TNO y , and HCHO, probably caused by model grid dilution or lower model emissions. The EMEFS diurnal component owes its variance to the daily photochemistry and nighttime dry deposition of the chemical species. In comparison, the matching ADOM component underpredicts the ratio [O 3]/([TNO y ]−[NO x ]) and the NO 2 consumption and O 3 production but overpredicts the contributions to the other species. The EMEFS emission component represents emissions from local/regional area sources. The corresponding ADOM component underpredicts TNO y by 44% and the fraction of TNO y as NO x compared to the EMEFS component, suggesting that the model has lower emissions of NO x and a photochemical mechanism that converts NO x faster than indicated by the EMEFS results.

Dry deposition velocity of O3 over a vineyard obtained from models and observations: The 1991 California ozone deposition experiment

Measurements were made of concentrations and flux densities (using the eddy correlation technique) for O3 over a vineyard for 20 days during July and August 1991. These were compared with modelled dry deposition velocities (V d), using (a) a module in the air quality model known as ADOM (Acid Deposition and Oxidant Model), which was modified to apply over a specific site, (b) a version of the ADOM module that employs a modified canopy resistance and (c) versions of ADOM which use two new canopy resistance formulations that are referred to as Wesely and Massman, respectively. The Massman parameterization is valid only locally since it was tuned to the site's ozone data. Here it is used as a benchmark for model comparisons. The observed V dhad an average value of about 0.5 cm s−1 during the day and about 0.2 cm s−1 at night. Compared to the modified ADOM, the new parameterizations yielded results that were in better agreement with the observations at night. During the daytime, the original ADOM and the Wesely estimates were much larger than the observations, the Massman values were slightly smaller, and the modified ADOM showed a better agreement. We speculate that the underestimation of the Massman V dvalues during the day may have been caused by the ADOM aerodynamic resistance rather than the Massman canopy resistance. It is hypothesized that the original ADOM module and its modified version may need a revised aerodynamic or an additional canopy resistance at night in order to bring the estimates closer to the observations.

A comparison of some aerodynamic resistance methods using measurements over cotton and grass from the 1991 California ozone deposition experiment

Measurements of dry, deposition velocities (V d ) of O3 (using the eddy correlation technique) made over a cotton field and senescent grass near Fresno California during July and August 1991 were used to test some dry deposition velocity models. Over the cotton field, the observed maximum daytimeV d was about 0.8 cm s−1 and the average nighttime value was about 0.2 cm s−1. Over the grass, daytime values averaged about 0.2 cm s−1 and nighttime values about 0.05 cm s−1. Application of a site-specific model known as ADOM (Acid Deposition and Oxidant Model) over the cotton field generally overestimated the observations except for a few hours in the afternoon when the observations were underestimated The overestimation was attributed to inadequacies in the surface resistance formulation and the underestimation to uncertainties in the aerodynamic formulation. Unlike previous studies which focused on the role of surface resistance, we perform additional tests using a large variety of aerodynamic resistance formulae, in addition to those in ADOM, to determine their influence on the modelledV d of O3 over, cotton. Over grass, ADOM considerably overestimated the observations but showed improvement when other surface resistance formulations were applied.

The sensitivity of regionally averaged O3 and SO2 concentrations to ADOM dry deposition velocity parameterizations

Abstract The influence of three different surface resistance formulations upon the resulting grid-averaged dry deposition velocity and the concentrations of O3 and SO2 calculated using the Acid Deposition and Oxidant Model (ADOM) has been investigated. Four ADOM simulations of the O3 and SO2 concentrations were compared with each other and the observations. The results show that two of the resistance formulations can decrease the original ADOM area-averaged dry deposition velocity by as much as 50% and increase the corresponding concentration by as much as 37% for O3 and SO2. However, all versions of the ADOM considerably underpredict the concentrations, implying weaknesses in ADOM that are not related to dry deposition. Wet surfaces appeared to have little influence on the estimated dry deposition velocity and concentration of O3 but had a strong influence on those for SO2.

Dry deposition velocity estimates of SO2 from models and measurements over a deciduous forest in winter

Measurements were made of concentrations and vertical flux densities (using the eddy correlation technique) for SO2 over a deciduous forest during March and April 1990. These were compared with estimates of dry deposition velocities, obtained from resistance analogue models that employ measured meteorological data as input. The models include: (1) the dry deposition module that forms part of a larger Eulerian air quality model, known as ADOM (Acid Deposition and Oxidant Model), (2) a modified version of ADOM and (3) a new parameterization for Rc. The observations yielded Vdvalues of about 0.5 cm s−1 for the daytime and 0.1 cm s−1 at night. ADOM's estimates were much larger, averaging about 3.0 cm s−1 during the daytime and about 2.0 cm s−1 at night. When the ADOM canopy resistance was increased by modifying its formulation, the modified dry deposition estimates were slightly larger during the day than at night, averaging about 0.5 cm s−1. The new parameterization for Rcyielded smaller Vdestimates with no diurnal variation. An attempt is made to relate the observed diurnal cycle of the dry deposition velocity to meteorological parameters.

Evaluation of the Eulerian acid deposition and oxidant model (ADOM) with summer 1988 aircraft data

Abstract Aircraft measurements from the Eulerian Model Evaluation Field Study (EMEFS) summer of 1988 intensive are compared with predictions of the Acid Deposition and Oxidant Model (ADOM). Aircraft measurements have been compared to surface measurements. Concentrations of H 2 O 2 from surface measurements were less than those at the base of the profile but O 3 , SO 2 and NO 2 agreed well. The horizontal variability in concentration over the approximate area of one ADOM grid square was examined and regionally representative values were defined for comparison with model-calculated values. ADOM simulates O 3 relatively well, although it does not predict the full concentration range. Underpredictions of sulphur, NO 2 and H 2 O 2 are seen aloft.

Correcting RADM's sulfate underprediction: Discovery and correction of model errors and testing the corrections through comparisons against field data

Abstract A serious underprediction of ambient sulfate (SO42−) by two comprehensive, Eulerian models of acid deposition, the Regional Acid Deposition Model (RADM) and the Acid Deposition and Oxidant Model (ADOM), was found in the National Acid Precipitation Assessment Program phase of the Eulerian Model Evaluation Field Study (EMEFS) model evaluation. Two hypotheses were proposed to explain the cause of the underprediction in RADM: insufficient SO42− production by nonprecipitating convective clouds and insufficient primary SO42− emissions. Modifications of the RADM cloud and scavenging module to simulate nonprecipitating cumulus clouds better are described in detail. Three contrasting pairs of tests using data from the EMEFS were applied to these hypotheses: source vs downwind regions, mid-summer vs late summer seasons and sunny-dry vs cloudy-wet synoptic types. The SO42− emissions hypothesis, tested by artificially boosting SO42− emissions, fared better than expected but was rejected because of its poor performance on the regional and seasonal contrast tests. The RADM nonprecipitating cumulus modification successfully captured the seasonal and the late summer synoptic contrasts but improvement is still needed for the regional and mid-summer synoptic contrasts.

The role of non-precipitating clouds in producing ambient sulfate during summer: Results from simulations with the Acid Deposition and Oxidant Model (ADOM)

Abstract A comprehensive acid deposition model was used to investigate the importance of non-precipitating stratus clouds for the production of ambient sulfate. A comparison of model estimates of ambient sulfate and SO 2 concentrations with corresponding observations for an episode in the summer of 1988 showed that the model underestimated ambient sulfate concentrations and overestimated ambient SO 2 concentrations when non-precipitating stratus clouds were ignored in the model formulation. When the model was modified to include non-precipitating stratus clouds, a distinct improvement in model performance was obtained.

Modelled and observed dry deposition velocity of O3 above a deciduous forest in the winter

Meteorological and air quality data were collected within and above a leafless deciduous forest during March and April of 1990. Included were measurements of O3 fluxes, using the eddy correlation technique, to obtain dry deposition velocities. These observations were used to investigate the capability of the dry deposition module that forms part of an existing Eulerian air quality model, known as ADOM (Acid Deposition and Oxidant Model). The observed dry deposition velocities of O3 (Vd) had an average daytime value of 0.3 cm s−1, compared to the summer value of 1.0 cm s−1, reported by Padro et al. (1991, Atmospheric Environment25A, 1689–1704). For the diurnal cycle, the model overestimated Vd by about 215% in the nighttime and 75% in the daytime. After making adjustments to canopy parameters and formulating the canopy resistance in terms of surface aie temperature the errors reduced to 115% in the nighttime and 34% in the daytime. A further modification to ADOM, incorporating Wesely's (1989, Atmospheric Environment23, 1293–1304) canopy resistance model, yielded Vd values for the diurnal cycle that were smaller than the observations by about 24% in the nighttime and 25% in the daytime. The possible influences of the solar radiation, the surface air temperature, the ground temperature and the canopy wetness on Vd are discussed by analysing their time-averaged diurnal cycles and their temporal variations for some days that are classified by sky and ground conditions.

The development of the acid deposition and oxidant model (ADOM)

This paper describes the development and testing of the Acid Deposition and Oxidant Model (ADOM), a nine-year project funded by a consortium consisting of Environment Ontario, Environment Canada, the German Umweltbundesamt, and the Electric Power Research Institute. The project consisted of three major phases: a design phase, an implementation phase, and an evaluation phase. In the design phase, the system being modeled was divided into its components—transport, gas phase chemistry, aqueous phase chemistry, dry deposition and cloud processes. The formulation of the modules for each of these processes was guided by the requirement that the modules reflect the state of the art, and at the same time be consistent with the available numerical resources. In the implementation phase, submodels were constructed, and then subjected to several tests, which included mathematical consistency checks, sensitivity studies, and evaluation against field and laboratory data. The modules were then assembled and interfaced with the input data sets. The codes for the modules as well as the overall model were vectorized to take advantage of the capabilities of supercomputers such as the CRAY. The North American and West German versions of the model are being tested against data collected in North America and in Europe. This paper describes the evaluation of ADOM with data associated with a regional ozone episode in Ontario in June 1983, and measurements made during an experiment to study the scavenging characteristics of spring storms in the central and northeastern United States in April 1981.

Sensitivity of ADOM dry deposition velocities to input parameters: A comparison with measurements for SO2and NO2over three land use types

Abstract Dry deposition velocity measurements of SO2 and NO2 over a deciduous forest, a carrot field and a snow surface are compared with estimates obtained from the dry deposition module in the regional Eulerian Acid Deposition and Oxidant Model (ADOM). The comparison with measurements taken in the fall and winter shows large model overestimates, sometimes as large as a factor of 5. The NO2 estimates are particularly poor and support existing evidence that models that employ the constant flux assumption for NO2 are inadequate. The canopy and the snow surface resistances are the largest contributors to the total resistances for SO2 and NO2, except for situations in which some of the snow turns into liquid water, when the aerodynamic resistance becomes important. Increasing the magnitudes, taken from measurements, of the ADOM original values for the stomatal, cuticle, ground and snow resistances and decreasing the NO2 mesophyll resistance and the Leaf Area Index (LAI) yield improved model results, particul...

An investigation of the ADOM dry deposition module using summertime O3 measurements above a deciduous forest

The dry deposition module in the Acid Deposition and Oxidant Model (ADOM) has been isolated from the complete model to accept local meteorological measurements in order to provide local estimates of dry deposition velocities. These are compared with observed O3 data obtained during the summer of 1988 over a deciduous forest. The comparison shows that the model systematically overpredicts by about 70% the dry deposition velocity for two selected days and for the average diurnal variations, obtained from the entire observed time series for July and August of 1988. The canopy resistance, to transfer of O3, is the major contributor to the model's total resistance for O3. In addition to the possible errors due to the “Big Leaf” approximation, sensitivity studies show that key parameters for reducing the systematic bias in the model are the Leaf Area Index, as well as mesophyll, stomatal, ground and cuticle resistances. For dry deposition velocities of SO2, the model also shows sensitivity to these parameters as well as the canopy wetness. A brief discussion on some mathematical approximations in the model is provided.

Testing a comprehensive acid deposition model

This paper describes the development and evaluation of a comprehensive acid deposition model referred to as ADOM (Acid Deposition and Oxidant Model). The first part of the paper describes the general approach to the formulation of the model. The second part presents the evaluation of the model against observations collected during the OSCAR (April 1981) field study. Although the model performs well in explaining the magnitudes and variations of the observations, the discrepancies between model predictions and observations are not small. Because of the uncertainties in the data used to run and evaluate the model, these discrepancies do not necessarily suggest the need for modifications in the model. Therefore, we have supplemented the direct comparison of model predictions with observations with indirect methods that establish the correspondence between the model and reality. This paper describes one such technique that relies on the washout ratio, which is sometimes used to characterize scavenging of pollutants.