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.

     

A method for developing ozone exposures that mimic ambient conditions in agricultural areas

Ozone fumigations that mimic ambient ozone distributions facilitate the development of links between

• 1.(1) vegetative effects results that are generated in the laboratory and the field and
• 2.(2) predictive effects models that depend upon ambient air quality data.

Experimental exposure profiles were constructed from a readily available ambient air quality data base (i.e. EPA SAROAD). Air quality data from selected monitoring sites were characterized over the 5-month growing season by identifying

• 1.(a) the number of occurrences of hourly ozone concentrations equal to or above 0.07 ppm,
• 2.(b) the number of days of each episode,
• 3.(c) the number of days between episodes and
• 4.(d) the rate of rise and decline of the daily ozone concentrations.

An episodic profile was constructed incorporating the information into a representative 30-day ozone exposure pattern in which the concentration was changed on an hourly basis. In order to compare treatments having equivalent exposures (sum of hourly ozone concentrations equal to or above a minimum value) but dissimilar temporal distributions of hourly concentrations, a second profile was created. This profile was characterized by a repeated daily incremental rise and decline in ozone concentration that had the same hourly maximum concentration each day. The use of experimental exposure profiles mimicking ambient air quality characteristics and applied under controlled experimental conditions permits the examination of important exposure parameters on plant response.     

Inter-storm comparisons from the OSCAR high density network experiment

The high density network component of the Oxidation and Scavenging Characteristics of April Rains (OSCAR) experiment combined aircraft, surface and sequential precipitation chemistry measurements to characterize the physicochemical and dynamic features of four storms sampled during an April 1981 field investigation. A surface network of 47 precipitation sampling stations, covering a region roughly 110 km by 110 km, was established in the area surrounding Fort Wayne, Indiana. The network provided temporal and spatial resolution of rainfall chemistry via the use of specially designed automatic sequential bulk precipitation collectors, while aircraft and surface sampling provided measurements of the major aerosols and trace gases in the boundary-layer inflow region.Composite concentration and ion ratio profiles for the events were analyzed to investigate potential pollutant scavenging pathways. This analysis led to the following observations:

• 1.(i) dryfall deposition during pre-rainfall exposure periods influenced initial sampler stage chemistry;
• 2.(ii) relative precipitation acidity increased throughout the events; SO₄²⁻ and NO₃⁻ were the major contributors to this acidity;
• 3.(iii) evidence exists for the in-cloud oxidation of SO₂ during Events 3 and 4, while scavenging of HNO₃ and aerosol NO₃⁻ probably produced precipitation NO₃⁻;
• 4.(iv) the non-frontal meteorology of Event 3 influenced the precipitation chemistry associated with this storm and led to distinct concentration profiles;
• 5.(v) an anomalous pattern of NH₄⁺ concentrations observed during Event 1 cannot be explained by known NH₄⁺ scavenging behavior or by non-scavenging related influences, such as local source contamination or NH₃ volatilization;
• 6.(vi) Event 4 is more suitable for analysis by one- and two-dimensional diagnostic wet removal models. Analysis of the other events is complicated by more complex meteorological behavior and, in some cases, a less complete chemistry data set. This paper enlarges on these observations with comparisons of the major meteorological and chemical characteristics of the four events.

     

Results from the Total Exposure Assessment Methodology (TEAM) study in selected communities in Northern and Southern California

Volatile organic compound levels (VOCs) in breath, personal air, fixed outdoor air and drinking water samples were measured and compared for a probability sample of individuals in Los Angeles and Antioch/Pittsburg, California during 1984. In addition, comparisons were made between seasons (winter vs spring) in Los Angeles for individuals sampled in both seasons. The statistics presented to compare the sites and seasons were primarily percent measurable and concentration levels (e.g. sample medians). For most comparisons, 13 VOC levels were examined for breath, personal and outdoor air samples and four VOCs for water samples.In addition to the results for VOC levels, the paper also briefly describes

• 1.(i) the sampling procedures used to obtain the study participants
• 2.(ii) the collection of air, breath and water samples
• 3.(iii) selected results from the quality assurance procedures used in this study.

For most chemicals, the percent measurable and concentration levels were

• 1.(i) higher in personal air samples than in breath or outdoor air samples,
• 2.(ii) higher in Los Angeles in the winter for air and breath than in the, spring,
• 3.(iii) higher in Los Angeles for air and breath than in Antioch/Pittsburg,
• 4.(iv) quite different for water as compared with air and breath.

Ubiquitous compounds in water were chloroform, bromodichloromethane, dibromochloromethane and bromoform while in air and breath they were 1,1,1-trichloroethane, benzene, tetrachloroethylene, ethylbenzene and the xylenes.Concentrations were higher in

• 1.(i) outdoor air vs breath in the winter in Los Angeles (where outdoor air levels were much higher than in the spring),
• 2.(ii) in personal air vs outdoor air in the upper tails of the concentration distribution (90th percentile) compared to the 50th percentile. For the water samples, relatively high concentrations were noted for chloroform, bromodichloromethane and dibromochloromethane.

In most cases, water concentrations were higher for Los Angeles in the spring. Five VOCs known to be in tobacco smoke (benzene, styrene, ethylbenzene and the xylenes) had significantly higher levels in the breath of smokers.     

On the nature of nitrate particles in a coastal urban area

Application of micro spot and electron microscopy techniques to individual particles in a coastal urban site revealed the following:

• 1.(a) sulfate particles, some of them mixed, dominated the sub-μm (0.3–0.8 μm) size range;
• 2.(b) nitrates were found mostly in the μm size range, in the form of NaNO₃.

The latter was verified by X-ray analysis of individual nitrates. Apparently the NaNO₃ particles were formed through heterogeneous reaction of gaseous HNO₃ with sea salt particles.     

Influence of selected fixed parameters on pulse-jet fabric filter operation

The effect of (a) fixing the time interval between cleaning pulses or (b) fixing the maximum pressure drop at which cleaning is started, on the performance of the fabric filter was investigated.A maximum pressure drop value of 2500 Pa:

• 1.(a) minimized the effect of the filter medium resistance;
• 2.(b) reduced the energy consumption by the filter;
• 3.(c) minimized the dust emission from the fabric filter to the surrounding atmosphere.

     

Evidence of ozone injury to a crop plant in India

Evidence is presented to show that a serious leaf spot disease of potato which appeared each year in the Punjab since 1978 is primarily due to ozone:

• 1.(i) The symptoms of the leaf spot were similar to the ozone stipple of potato reported in the U.S.A.
• 2.(ii) Activated charcoal and ethylenediurea effectively controlled the spots.
• 3.(iii) Elevated ozone in the atmosphere was detected with the bioindicators Nicotiana tabacum var. Bel-W3 and potato variety Cherokee. This is the first report of ozone injury to a crop plant in India.

     

Report on a British Council specialist tour to India

This Report describes a tour from 2 to 14 January 1986 in Delhi and New Delhi. The principal objectives were:

• 1.(1) To participate in the Indian Science Congress Meeting.
• 2.(2) To present a paper in the section on ‘Recent advances in numerical modelling of the disperion of atmospheric pollutants’ and make an appraisal of the value of the meeting and suggestions for future meetings.
• 3.(3) Discuss the research programme of the Centre for Advanced Studies in Atmospheric and Fluid Sciences of the Indian Institute of Technology with staff and research students and make recommendations for the future direction and development of this programme.
• 4.(4) Participate in seminars and discussions at the Centre. A general impression of the Indian air pollution scene is also given, and its relationship to past and present situations in other parts of the world is discussed.

     

The role of nitrogen oxides in nonurban ozone formation in the planetary boundary layer over n America,w europe and adjacent areas of ocean

The status of knowledge on photochemical ozone formation and the effects of nitrogen oxides and peroxyacyl nitrates on such formation have been evaluated. The literature is reviewed on

• 1.(a) nonurban ozone and nitrogen oxide concentration distributions,(b) ozone lifetimes,(c) nitrogen oxide lifetimes, and(d) ozone formation in plumes as related to nitrogen oxide.

The modeling approaches applied to ozone formation

• 1.(a) with urban plumes,
• 2.(b) power plant plumes,
• 3.(c) high pressure systems, and
• 4.(d) during longerrange transport of ozone are discussed. In addition, models concerned with the contributions to ozone formation associated with reactions of natural hydrocarbons and nitrogen oxide near ground level and photochemical ozone formation associated with reactions of carbon monoxide and of more persistent organic species with nitrogen oxides in the free troposphere are considered.

It is concluded that urban plumes are major contributors to elevated ozone concentrations measured at nonurban locations, particularly during the passage of high pressure systems. Ozone can survive at significant concentration levels for more than one day of transport. However, the evidence for multiday ozone transport is to a large extent associated with transport over water.Ozone formation during the first day of transport does not appear to be limited by the availability of nitrogen oxides. However, it is likely that multiday formation and transport of ozone within the boundary layer is limited in duration because of the relatively short lifetimes of nitrogen oxides and peroxyacyl nitrates. Photochemical formation of ozone in the free troposphere may be an important contributor to longer-time average ozone concentrations in rural areas. These free tropospheric processes depend in part on anthropogenic sources of precursors and are especially sensitive to the vertical distribution of nitrogen oxides in the atmosphere.     

Characterization of large particles at a rural site in the eastern United States: Mass distribution and individual particle analysis

A unique combination of an effective sampler and analysis of individual particles has been used in studying large particles (> 5 μm) at a rural site in eastern United States. The sampler is a modified ‘high volume’ rotary inertial impactor, which consists of four collectors of different widths, rotating at high speed and collecting particles by impaction. The collector surfaces were Mylar films coated with apiezon to ensure retention. After sampling, the collection surfaces were weighted to obtain the mass-size distribution. A section of the Mylar sample was transferred to a scanning electron microscope to study in detail the morphology and elemental content of individual particles.Results from two case studies indicated the following conclusions could be made:

• 1.(a) Natural sources, minerals and biologicals, were the main contributors to large particles (> 5 μm),
• 2.(b) Contribution of anthropogenic sources, mainly coal-fired power plants emitting fly ash particles, was limited to a few percent of the 5–10 μm size range,
• 3.(c) Pollen and some of the minerals were enriched in sulfur, probably as accumulation of sulfate on the particle surface,
• 4.(d) At low wind speeds the anthropogenic contribution was enhanced, whereas at high wind speeds natural sources were almost the only contributors to the large particle mode.

In both cases the mass distribution of the large particles peaked at around 15 μm.     

Co-occurrence patterns of gaseous air pollutant pairs at different minimum concentrations in the United States

The frequency of co-occurrences for SO₂NO₂, SO₂/O₃ and O₃/NO₂ at rural and remote monitoring sites in the United States was characterized for the months of May-September for the years 1978–1982. Minimum hourly concentrations of 0.03 and 0.05 ppm of each gas were used as the criteria for defining a ‘co-occurrence’. The objectives of this study were to:

• 1.(1) identify the types of co-occurrence patterns and their frequency;
• 2.(2) identify whether the frequency of hourly simultaneous co-occurrences increased substantially when the minimum concentration was lowered (e.g. from 0.05 to 0.03 ppm) for each pollutant; and
• 3.(3) determine whether the frequency of co-occurrences showed large year-to-year variation.

For all pollutant pairs and co-occurrence thresholds (i.e. 0.03 and 0.05 ppm), the frequency of daily and hourly co-occurrences was low for most sites. Year-to-year variability was found to be insignificant; most of the monitoring sites experienced co-occurrences of any type less than 12% of the 153 days. Based on our observations, researchers attempting to assess the potential effects of SO₂/NO₂, SO₂/O₃ and O₃/NO₂ in the United States should construct simulated exposure regimes so that

• 1.(1) hourly simultaneous and daily simultaneous-only co-occurrences are fairly rare and
• 2.(2) when co-occurrences are present, complex-sequential and sequential-only co-occurrence patterns predominate.

     

Development of a MnO2-coated,cylindrical denuder for removing NO2 from atmospheric samples

In order to develop a diffusion denuder for the removal of NO₂ from ambient atmospheric samples, a number of materials were screened for their ability to adsorb NO₂:

• 1.(1) MgO;
• 2.(2) MnO₂ on alpha-Al₂O₃;
• 3.(3) water-treated MnO₂ on alpha-Al₂O₃; and
• 4.(4) MnO₂ (activated).

A simple cylindrical denuder coated with MnO₂ (activated) was very effective in the removal of NO₂ from a feedgas of NO₂ in air at ambient temperature and pressure. The other materials were unsatisfactory. The strong oxidizing properties, along with the hydrated surface of the MnO₂ (activated), appear to be important for the sorption of NO₂, as suggested in applications elsewhere. Quantification of denuder sorption efficiencies indicates that MnO2 (activated) is nearly a perfect sorbent for NO₂. The diffusion coefficient of NO₂ in air was found to be 10.8 ± 0.3 cm² min⁻¹ at 22–23°C, which compares favourably with a theoretical estimate. Although MnO₂ (activated)-coated denuders were also found to adsorb SO₂, interference with NO₂ sorption was not sufficient to impair ambient applications.     

Modeling distributions of air pollutant concentrations—I. Identification of statistical models

In this paper the process by which a distributional model may be identified from a range of alternative models is examined. An assessment of the methods by which goodness-of-fit may be evaluated is presented. A procedure for selecting amongst the exponential, gamma, lognormal and Weibull distributions has been applied to 24-h average suspended particulates (β-scattering), ozone, carbon monoxide, sulphur dioxide, oxides of nitrogen, nitrogen dioxide and nitrogen oxide observations recorded in Melbourne, Australia. It is shown that

• 1.(a) lognormal distribution is appropriate for particulate data and the majority of the nitric oxide, oxides of nitrogen and sulphur dioxide data sets
• 2.(b) gamma distribution is best for both carbon monoxide, nitrogen dioxide and ozone
• 3.(c) Weibull distribution is appropriate for a significant number of carbon monoxide and ozone data sets.

     

Continuous four-dimensional source attribution for the Berlin area during two days in July 1994. Part II: Sensitivity studies

The multiple nested three-dimensional (3D) mesoscale Eulerian grid point model MM5 is directly coupled with a Lagrangian particle trajectory model in order to perform a four-dimensional source attribution for the area of Berlin based on the horizontal distribution of the import probability density (IPD). The technical aspects are already demonstrated in the companion paper A (Part I) including the illustration of the meteorological situation at the two consecutive days of investigation and a primarily 3D source attribution. We conducted further sensitivity studies concerning the effect of vertical mixing, the static stability of the particles/emissions and the regarded time scale on the IPD distribution which is extended to four dimensions. The main results are:

• •Heterogeneity and temporal variability of the wind field enhance the contributions of nearby sources (emissions) to the total import of the receptor in contrast to stationary wind fields which increase the scope of the IPD distribution in the upstream direction.
• •Regions of static stability, for example morning hour inversion layers, enhance the contribution of far distance sources with longer import times.
• •The import velocities increase, as far as long distance source-receptor transitions are concerned, because they are mostly realised via higher transport paths.
• •The third (vertical) dimension is not negligible for the task of a complete source attribution, as a considerable amount of elevated emissions, preferably out of 300±100 m elevation, reaches the receptor box which is only 50 m in depth. Hence, downward mixing of elevated and far distance sources is an important process and driven by the diurnal course of turbulence and low level jets within the PBL
• •On the short time scale (few days), the source attribution is not independent from the regarded time scale (simulation time) due to the neglecting of older emissions released before the beginning of the simulation.

     

Coal particle dispersion monitoring system

A monitoring system for coal panicle dispersion at coal storage yards is necessary to meet environmental standards for the operation of coal fired power plants. We have developed a system having three functions as follows:

• 1.(1) To measure coal particle concentrations at the first connecting part of belt conveyors.
• 2.(2) To predict occurrence of coal particle dispersion during stacking.
• 3.(3) To moisten the coal at the second connecting part of belt conveyors when coal particle dispersion occurs.

The generation of coal dispersion is determined by whether or not the hygroscopic moisture is greater than the critical hygroscopic moisture value for each coal type. Coal particle concentrations are measured using dust meters. In this report, the dust meter readings were related to emission rate of coal particle and dustiness index of coarse dust defined by ASTM D547-41 in order to predict occurrence of coal particle dispersion using dust meters.The adaptability of the system to real coal handling facilities was examined by a model which consisted of belt conveyors, a stacker, connecting parts and the monitoring system. As a result of these experiments, it was demonstrated that coal particle dispersion can be suppressed by means of wetting coal in response to dust meter readings.     

Total SO2 emission control strategies for the management of air pollution in ulsan industrial complex

Since emission regulations in Korea concentrate mainly on the limitation of pollutant concentration in the stack gas, it is difficult to achieve a desirable air quality in a heavily industralized city like Ulsan. To ensure a suitable air quality in the future, a total emission control method is proposed with a stack height formula of H = 10.6 q^0.5, where H is the stack height (m) and q is the SO₂ emission rate (m³ h⁻¹ reduced to 0°C). The total emission permitted can be allocated to industries

• 1.(1) at an uniform reduction rate,
• 2.(2) by the formula Q = aQ_o^0.925, where Q is the emission allowed (g s⁻¹), a is a constant, and Q_o is the emission before control (g s⁻¹), or
• 3.(3) by using a linear programming technique.

The above three approaches were evaluated using the TCM 2 air quality model. In order to achieve the air quality goal set for the area, the first approach requires 38.7 % reduction of SO₂ emission from industries, the second 53.3 %, and the third 4.3 %. The linear programming method is found to be very economical, but there are some administrative difficulties in enforcement.     

Inherent uncertainty in air quality modeling

This paper summarizes the discussions of a working group that was charged with the task of examining inherent uncertainty in air quality modeling. The major topics of the paper are:

• 1.1. Definition of inherent uncertainty in air quality models;
• 2.2. Determination of inherent uncertainty;
• 3.3. Role of inherent uncertainty in model evaluation.

The concepts introduced here are illustrated through a numerical simulation with Gifford's fluctuating plume model.     

Five years of air chemistry observations in the Canadian Arctic

Arctic air chemistry observations made in Canada between 1979 and 1984 are discussed. The weekly average concentration of 25 aerosol constituents has been measured routinely at three locations. Anthropogenic pollution typified by SO₄²⁻ and V has a persistent seasonal cycle. SO₄²⁻ concentrations are similar at all three locations, although they tend to be somewhat higher at Alert than at Mould Bay and Igloolik. The seasonal variation of an aerosol constituent depends on its source. There are four distinctive seasonal variations for:

• 1.(i) anthropogenic constituents Cr, Cu, Mn, Ni, Pb, Sr, V, Zn, H⁺, NH₄⁺, SO₄²⁻, NO₃⁻,
• 2.(ii) halogens (excepting Cl) Br, I, F,
• 3.(iii) sea salt elements Na, Mg, Cl and
• 4.(iv) soil constituents Al, Ba, Ca, Fe and Ti. In the Arctic winter, the mean concentrations of anthropogenic aerosol constituents, except SO₄²⁻, are 2–4 times lower than annual mean concentrations in southern Sweden near a major source region. SO₄²⁻ concentrations are only 30% lower mainly because of production from SO₂. Light scattering (b_scat) and SO₄²⁻ observations indicate that the SO₄²⁻ fraction of the fine particle mass fluctuates between 3 and 65% during the polluted winter months. Daily mean b_sact, at Mould Bay that exceeds 50 × 10⁻⁶m⁻¹ is associated with air originating from the northwest. The soluble major ion composition of aerosols during winter varies markedly with particle size. H⁺, NH₄⁺ and SO₄²⁻ dominate submicrometre particles while sea-salt ions Mg²⁺, Na⁺ and Cl⁻ predominate in supermicrometre particles. Winter SO₂ concentrations at Mould Bay and Igloolik ranged from 0.2 to 1.5 ppb
• 5.(v). The fraction of airborne S as SO₂ ranged from 20 to 90% and peaked in late December-early January. The concentration of total NO₃⁻ (0.025–0.090 ppb(v)) is much lower than that of SO₄²⁻ (0.3–1.2 ppb (v)).

     

A residence time probability analysis of sulfur concentrations at grand Canyon National Park

A statistical method is developed to determine the locations of major pollutant sources affecting a distant downwind receptor, provided that air trajectories can be estimated. Probability density functions are estimated which indicate

• 1.(1) the overall residence time of air parcels over a given geographic region as they travel toward a receptor and
• 2.(2) residence time for the case of high pollutant concentrations at the receptor.

These functions are used to estimate a conditional probability function which indicates the potential for a source region to contribute to high air pollution concentrations. Finally, a source contribution function is formulated to indicate the relative contribution of different source regions to high concentrations at the receptor. The method is tested using data collected at Grand Canyon National Park in 1980. The dominant pathway for air masses arriving at Grand Canyon during this period was southern California. A lesser pathway was from the border of Utah and Colorado and a minor pathway was from southern New Mexico. The potential source regions of sulfur particles were (in descending order) southern New Mexico, southern California and eastern Nevada. The source contribution function, however, shows that southern California contributed the most high sulfur concentration episodes in 1980, followed by eastern Nevada and southern New Mexico.     

Air quality model performance: A comparative analysis of 15 model evaluation studies

This paper presents a comparative analysis of the results of 15 air quality model performance evaluation studies involving 35 rural, urban, complex-terrain and regional models. Common themes are identified, and their implications for the improvement of model performance and usage discussed. Among study findings are the following:

• 1.(a) flat-terrain rural models nearly always predict the second highest concentrations within a factor of two (often less), with no evidence of systematic over- or underprediction, but some models may underpredict the highest concentrations by more than a factor of two at distances far downwind (20 km);
• 2.(b) none of the models accurately predicts spatial patterns of ⩽ 24 h-averaged concentrations, and while increasing the averaging time from 24 h to annual improves performance for some models, it does not appear to do so for flat-terrain rural models; and
• 3.(c) while some models appear to predict more frequent concentrations (e.g. 5th- or 10th high, 95th percentile) better than they do the highest concentrations (e.g. 2nd high), no overall, systematic tendency is evident. Although definitive proof is beyond the scope of this paper, the hypothesis is offered that the observed performance of flat-terrain rural models may be attributable, in part, to slower-than-actual cross-sectional plume dispersion under neutral and stable atmospheric conditions, particularly in the vertical direction, but possibly also in the horizontal.