Meteorology of long-range transport

The increasing attention to regional-scale transport of pollution has resulted in numerous air quality networks, models and large scale field studies to relate the sources of pollution to subsequent air quality measurements and thence to the effects of pollution. We compare observed air quality and trajectory data to calculations to quantitatively evaluate the differences. Methods of preparing air trajectories are described with emphasis on the Air Resources Laboratories' trajectory model and an accompanying diffusion model. The comparison of observed atmospheric transport with calculated trajectories shows that large computational errors can occur and more importantly that these may be systematic, but different, depending on the type of advection (cold vs warm) and whether the transport is over land or over the sea. We describe the use of tetroon recovery locations in trajectory analysis and show that such data can be obtained over distances up to 4000 km. Computed trajectories based on the geostrophic assumption and on the observed wind field are compared to observations to determine the adjustments required to obtain the best comparisons. Directional adjustments of up to 40° and changes in speed by a factor of two are sometimes necessary. We make suggestions for studies to improve the capability of calculating trajectories, including experiments using balloons and controlled tracer releases. Both of these techniques are applicable over regional scales. Finally we show the global distribution of sulfur from the industrial areas of the Northern Hemisphere, as calculated by an efficient computer model, as a step in the determination of the global sulfur budget.     

The contribution of middle- and long-range transport of tropospheric photochemical ozone to pollution at a rural site in North-West England

Ground-level ozone measurements from a rural site in North-West England are presented. Two distinct types of polluted air mass are identified: one type having passed over the North Sea and Northern England, and the other having travelled from the continent via the South-East and Midlands of England. The former air mass type contains long-range transported ozone originating primarily within continental Europe, whilst the latter type contains both long-range transported ozone and ozone formed from precursors injected during passage of the air mass over middle-distance source areas in England. The monitoring results are compared with the predictions of recent theoretical models of ozone formation in polluted air masses and urban plumes.     

Sensitivity study of air trajectory long-range transport modelling

A forward trajectory model for long-term regional scale simulation of transport and deposition of sulphur from a single elevated point source is used for sensitivity tests of the deposition pattern and suspension ratio, subject to a spatial and temporal variable mixing depth, contra constant mixing depth different oxidation rates of SO₂, wet deposition rates and different source heights. The deposition is studied up to 1800 km from the source using meteorological data measured every 6 h covering Europe. For dry conditions, the inclusion of a diurnally variable mixing depth causes longer residence times of the airborne S and larger deposition far from the source. An effective wet deposition rate, however, has a tendency to suppress the change in the dry deposited mass induced by variable mixing height. A change from an oxidation rate of about 1 to 3%h⁻¹ increases both the suspension ratio and the deposition significantly at large distances from the source, while a change to a low value, 0.5 % h⁻¹ has the opposite effect. Halving the wet removal rates results in about 30% larger deposition at remote locations and 30% lower deposition occurs when the removal rates are doubled. Similar changes occur in the suspension ratio. A low source causes about 60% higher local depositions and consequently reduced suspension ratios and distant depositions of about 30%. These results support the assumption that the uncertainty in predictions of total deposition and residence times is within about ±50% when the uncertainty in the parameters considered is taken into account.     

Modelling long-range transport of primary particulate material over Europe

This paper uses a simple model of atmospheric transport and an emissions inventory prepared by TNO to estimate the contribution of primary particulate material to PM₁₀ and PM_2.5 concentration across Europe. The resulting population exposure is compared with that of secondary particulates, and it is noted that both primary and secondary contributions will be significantly reduced with the implementation of new protocols under the Convention on Long-Range Transboundary Air Pollution (CLRTAP). Since concentrations of primary PM₁₀ can become elevated in episodic situations, when long-range transport of particulate could, on its own, exceed 24 h average targets of 50 μg m⁻³ over large areas of Europe, such reduction is important for achievement of current air quality standards to control exposure to atmospheric particulate PM₁₀.     

The long-range dispersion of a plume from an isolated point source

The dispersion of the plume from a sulphide smelter at Mount Isa, Australia, has been determined at distances of up to 1000 km from the source. Simultaneous measurements by an airborne correlation spectrometer, flame photometer and aitken counter have allowed accurate determinations of plume width at these large distances.Radiosonde and pilot-balloon data from four positions spanning the region have been used to calculate the trajectories of each of the plumes measured in the study. In each case the measured plume position was in good agreement with the position predicted on the basis of the wind data.A simple model based on the diurnal variation of the structure of the atmosphere, as well as the turning of the wind with height, is shown to account adequately for the measurements of plume width during well-mixed atmospheric conditions at distances of between 25 and 1000 km from the source.     

Assessment of the environmental persistence and long-range transport of endosulfan

Concentrations of the insecticide endosulfan (α- and β-isomer) and its degradation product endosulfan sulfate in air, seawater and soil are calculated with the global environmental fate model CliMoChem. As model input, physicochemical properties of all three compounds were assembled and a latitudinally and temporally resolved emission inventory was generated. For concentrations in air, model and measurements are in good agreement; a bimodal seasonality with two peaks in spring and fall as it is observed in Arctic air is reproduced by the model. For seawater, the agreement of model and measurements depends on the values of the hydrolysis activation energy of endosulfan used in the model; with relatively high values around 100 kJ/mol, model results match field data well. The results of this assessment of the levels, persistence, and global distribution of endosulfan are also relevant for the evaluation of endosulfan as a Persistent Organic Pollutant under the Stockholm Convention.     

Assessment of long-range transport potential of polychlorinated Naphthalenes based on three-dimensional QSAR models

Environmental Science and Pollution Research - Experimentally determined octanol–air partition coefficients (K OA) for 43 polychlorinated naphthalene (PCN) congeners and experimentally...     

Satellite detection of long-range pollution transport and sulfate aerosol hazes

While not designed for such a task, meteorological satellites now play a growing role in our understanding of long range transport of secondary pollutants. This paper reports on a demonstration project showing that currently available synchronous satellite data can detect the aerial extent and motion of large-scale “hazy” air masses associated with sulfate and ozone episodes. An interactive computer graphics system is utilized showing that digital satellite data can obtain precise measurements of upward scattered solar radiation which is correlated to aerosol optical thickness and therefore to sulfate concentrations. Measurements over Lake Michigan for instance, reveal over-water image brightness enhanced fully 60–70% as visibility estimates of fb_scatincreasedfrom 1.8 × 10⁴m⁻¹to 5.7 × 10⁻⁴m⁻¹.Digital satellite data is shown to have great promise in mapping sulfate haze areas, especially over water.     

Impact of long-range transport and under-cloud scavenging on precipitation chemistry in East China

Introduction  

Two hundred twenty-five precipitation samples were collected at high- (summit, 1,534 m ASL) and low-elevation (base, 218 m ASL) sites between 2005 and 2008 in eastern China. The present work focused on the roles of long-range transport and under-cloud/boundary layer scavenging on chemical composition of precipitation collected at the two sites.     

Simulations of stratospheric to tropospheric transport during the tropical cyclone Marlene event

Enhanced ozone values observed in the upper troposphere near intense tropical cyclones have raised the question of the role of stratospheric–tropospheric exchange. The dynamical mechanisms involved in the enhanced ozone values of 6 April 1995 observed at Reunion and associated with the tropical cyclone Marlene could not be explained by ECMWF meteorological analysis with 1.125° horizontal resolution. A previous study based on the ECHAM model has demonstrated the impact of biomass burning, but of limited amplitude (<60–80 ppbv max). In this paper, the upper tropospheric ozone enhancement on the periphery of Marlene has been studied with a mesoscale model (MESO-NH). This model is able to reproduce a stratospheric PV filament into the troposphere, crossing the isentropes to the 350 K level. The ageostrophic circulation associated with divergence zones that have induced vertical movements has been shown. Further, the influence of vertical wind shear, evident in both the mesoscale analysis and in the idealized HURRICANE tropical cyclone model, also contributes to our understanding of this downward transport process.     

Analysis of observations relevant to long-range transport and deposition of pollutants

Observations of annual wet deposition of sulfur made during 1980 at 62 stations in northeastern America are interpreted using a statistical long-range transport model. This work is meant to demonstrate the role of an empirical model in the analysis of observations. Our analysis points to the following conclusions:

• 1.(1) The parameters that represent the conversion of SO₂ to SO₄ and the wet and dry removal of sulfur are insensitive to concentration levels,
• 2.(2) the variation of the wet deposition field is closely related to the distribution of sulfur emissions and
• 3.(3) observations demand efficient wet scavenging of SO₂.

     

Chemical characteristics of long-range transport aerosol at background sites in Korea

In this study, background concentration sites of Deokjeok and Gosan, which were deemed suitable for monitoring the impact of long-range transported air pollutants, were selected. An investigation of the source types of pollutants, their locations, and relative quantitative contributions to the particulate concentrations at both sites using appropriate methodologies to make initial estimations was conducted. Episodic measurements of PM_2.5, PM₁₀, and size distribution, along with its ion and carbon components were performed from 2005 to 2007, and a comprehensive analysis of the results was conducted utilizing back trajectory analysis. As for frequency of wind direction, it was quite apparent that the two sites are heavily influenced by air masses originating from the eastern and northern regions of China. For PM_2.5 and PM₁₀, the mass concentrations from north and east China were higher than other cases, originating from the ocean. In the northerly-wind case, meteorological properties for Deokjeok and Gosan and the influence of carbon emissions from northwest Korea resulted in a changing of air mass properties during transport. As was the case with mass concentration, the highest contribution for ionic and carbon components of PM_2.5 and PM₁₀ for both sites appeared for the westerly wind case. A specially high relative contribution, greater than 1.4 times, was apparent in the secondary aerosol case because of a large influence of long-range transported pollutants from east China. Carbon components exhibited different behaviors for the northerly and westerly wind cases compared with secondary aerosol. The major reason for this discrepancy appears to be the carbon emissions from northwest Korea.     

Mesoscale influence on long-range transport — evidence from ETEX modelling and observations

During the first European Tracer Experiment (ETEX) tracer gas was released from a site in Brittany, France, and subsequently observed over a range of 2000 km. Hourly measurements were taken at the National Environmental Research Institute (NERI) located at Risø, Denmark, using two measurement techniques. At this location, the observed concentration time series shows a double-peak structure occurring between two and three days after the release. By using the Danish Emergency Response Model of the Atmosphere (DERMA), which is developed at the Danish Meteorological Institute (DMI), simulations of the dispersion of the tracer gas have been performed. Using numerical weather-prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF) by DERMA, the arrival time of the tracer is quite well predicted, so also is the duration of the passage of the plume, but the double-peak structure is not reproduced. However, using higher-resolution data from the DMI version of the HIgh Resolution Limited Area Model (DMI-HIRLAM), DERMA reproduces the observed structure very well. The double-peak structure is caused by the influence of a mesoscale anti-cyclonic eddy on the tracer gas plume about one day earlier.     

Analysis of long-range transport influences on urban PM10 using two-stage atmospheric trajectory clusters

There is evidence that long-range transport of natural and/or anthropogenic particles can have a negative impact on urban air quality. Certain European cities may fail to comply with the currently implemented 24-h PM₁₀ limit value due to the additional impact of remote sources of particles, which are not controllable at local level. For that reason, reliable methodologies identifying long-range transport patterns and quantifying their contribution to urban PM₁₀ levels are required. In this study, a two-stage clustering methodology was developed and applied to back trajectories arriving in three European cities: Athens, Madrid and Birmingham, which experience large, moderate and small numbers of daily PM₁₀ episodes, respectively. The atmospheric trajectories used in this analysis were computed with HYSPLIT model (NOAA) for a 3-year period. The two-stage cluster analysis has the advantage of providing highly disaggregated trajectory clusters, which proved to correspond to significantly different PM₁₀ levels. In the case of Madrid and Birmingham, clusters of trajectories originating from North Africa and continental Europe, respectively, were strongly associated with the highest PM₁₀ levels recorded in selected monitoring stations. In Athens, long-range transport patterns and trans-boundary influences were less evident, which highlighted the more substantial impact of local emission sources. Finally, two simple statistical indexes were proposed for assessing PM₁₀ episodes associated with different clusters of trajectories. This study has established a practical methodology for examining the impact of long-range atmospheric transport on local air quality, without resorting to high resource-demanding source apportionment techniques.     

The oxidation and long-range transport of sulphur dioxide in a remote region

The flux of sulphur dioxide has been measured in the plume of a remotely situated smelter (Mount Isa, Australia) at distances of up to 1000 km from the source. These measurements were made with an airborne correlation spectrometer in plumes ranging in age from 1.0 to 42.5 h, the latter corresponding to a photolytic age of almost two periods of daylight. Ground-based experiments were also performed to determine the rate of dry deposition of sulphur dioxide in the area situated about 500 km from the source.The implications of an error in the deposition velocities, reported by Milne J.W., Roberts D.B. and Williams D.J. (Atmos. Envir. 13, 373–380, 1979.), are considered. The average velocity for the Mount Isa region is higher than that previously employed by Roberts D. B and Williams D.J. (Atmos. Envir. 13, 1485–1489, 1979). Along with a reassessment of the diurnal model and the average mixing height encountered by Roberts and Williams, this necessitates a reduction in the estimate of the photochemical oxidation rate of sulphur dioxide from 0.25 to 0.15%h⁻¹, when averaged over 24 h.It is shown in this study that the rate of loss of sulphur dioxide from the plume out to the furthest distances measured can be accounted for by the combined processes of atmospheric oxidation and dry deposition, as determined by Roberts and Williams for much shorter distances (< 260 km). The lifetime of sulphur dioxide in the region under study is shown to be fourteen days, with about half of the loss being due to atmospheric oxidation.     

A framework for error analysis of a long-range transport model with emphasis on parameter uncertainty

A comprehensive framework for model error analysis is applied to the EMEP-W model of longrange transport of sulfur in Europe. This framework includes a proposed taxonomy of model uncertainties. Parameter uncertainties were investigated by Monte Carlo simulation of two source-receptor combinations. A 20% input parameter uncertainty (expressed as a coefficient of variation = standard deviation/mean) yielded a 15–22% output error of total sulfur deposition. The relationship between output error and input uncertainty was approximately proportional. Covariance between parameters can have an important effect on computed model error, and can either exaggerate or reduce errors compared to the uncorrelated case. Of the model state variables, SO₂ air concentration and wet deposition had the highest error, and total sulfur deposition the lowest. It was also found that it is more important to specify the dispersion of the input parameter frequency distributions than their shape. The results of the model error analysis were applied to routine calculations of deposition in Europe. An error (coefficient of variation) of 20% for transfer coefficients throughout Europe yielded spatial variations in the order of a few tens to a few hundreds of km in computed deposition isolines of 2 and 5 g sulfur m⁻²a⁻¹.     

Expanding box models for the long-range transport of chemically reacting airborne material

If a power station plume significantly perturbs the levels of chemically active species in the atmosphere, then the rates of chemical reactions become non-uniform across the plume. This results in different effective plume widths for the different chemical species, which in turn influence the reaction rates. Here coupled equations are derived which for a reaction involving a single oxidant accurately model the total amount of a species in a plume and the associated plume width. The conventional box model slightly underestimates the amount of oxidized material produced. It is therefore suggested that the sensitivity of plume models to assumptions regarding lateral mixing should be tested, using the system of coupled equations derived in the paper.     

Individual particle characteristics of North African dust under different long-range transport scenarios

After urban sources, mineral dust in Madrid is the second biggest contributor to PM₁₀, making up 40% on average, of total emissions. Approximately, 50% of the days on which the daily limit of 50 μg m^?3 marked by the European Directive, are ascribable to Saharan outbreaks. The present study has focused on individual particle characterization of North African dust over Madrid by SEM/EDX, since no previous works on this type of characterization have been found in the region. More than 30,000 particles from 6 different samples have been measured to characterize 4 African episodes with very different meteorological scenarios, transport processes and source origins. Different samples from the same episode have also been characterized to evaluate homogeneity of dust characteristics over time. Silicates, mainly composed of clay minerals, are the main component, with abundances ranging from 65 to 85% by particle volume. Chemical cluster distribution of silicates has been linked to the major topsoil mineralogical composition in the origin of the episodes. Aspect Ratio (AR) has been used to compare particle morphology between episodes. AR values from samples taken under the same scenarios are statistically equal. For all the samples and size ranges AR values are found to be in the same order: AR_sulphates > AR_silicates > AR_carbonates. Particles not only maintained morphology during the episode, but also chemical composition, since clusters turned out to be very similar in samples taken on the same day and different days. Similarities and differences in particle chemical composition and morphology between the different transport patterns are discussed in detail throughout the paper.     

A statistical model to estimate long-term concentrations of pollutants associated with long-range transport

A simple statistical model is presented for estimating long-term concentrations of pollutants associated with long-range transport. Dispersion and removal of pollutants are described in terms of statistics of these physical processes. The model has been used to estimate wet deposition of sulfur over a grid covering Northeastern United States and Canada. Model estimates compare well with corresponding measurements of annual deposition. As an example of the applications of the model we have computed the relative contribution of U.S. and Canada to the sulfur deposition over the grid considered in the paper.