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.     

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.     

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.     

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.

     

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.

     

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.

     

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.     

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.

     

Summary report of the corech (COGAR) workshop on the evaluation of air pollution episodes and associated control measures

Discussions within COGAR during 1981 indicated that collective information on the types of meteorological conditions when large, single sources like power stations contributed to pollution episodes, the frequency with which they occurred and the implications for intermittent control procedures, was important to all member utilities. This paper summarizes the findings of a working group set up by COGAR to study these problems.The investigation was concerned with SO₂ episodes and how feasible it would be to reduce their intensity by such measures as a substitution of low sulphur fuel or switching generation to areas where the probability of an episode developing is less.There has been a considerable reduction in SO₂ emissions in most urban areas in the last two decades. Nevertheless, in many locations, 24-h air pollution episodes can still be attributed to small or medium-sized emissions from low or medium level stacks, rather than to power stations and other large industrial sources with tall stacks. The worst cases in flat terrain where power stations do contribute for many hours are either stagnant conditions persisting for 24 h or a steady wind blowing consistently from an area containing several power stations. Single stations can present problems when topography interferes with dispersion or the stack height is inadequate for the emissions.Data on the frequency with which episodes occur in a given location and the ability to forecast episode conditions in advance, so that if appropriate, preventative measures may be taken, are the desired objectives. Achievement of these objectives requires a detailed understanding of the role of each type of source in relation to different meteorological situations and the local topography. The end product of such studies should be either;

• 1.(a) the specification of a procedure for implementing intermittent emission control
• 2.(b) a demonstration that intermittent control is not an effective option in the area under study.

In case (a), input data required are

• 1.(i) the vertical structure of the atmosphere
• 2.(ii) ground level concentrations of pollutant plus, in complicated topography
• 3.(iii) the three-dimensional distribution of pollutant.

COGAR is a group set up to coordinate atmospheric research in the electrical supply industry in Europe.     

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.

     

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.     

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.

     

Background levels of air and precipitation quality for Europe

This paper is intended to be used by specialists engaged in air and precipitation quality management on regional and continental scales. Major goals are to establish definition, methodology and specific values of background air and precipitation quality for sulfur (S) and nitrogen (N) species to be used in practical applications of air resources management. Major findings are the following:

• 1.(a) 69% of SO₂ and 63 % of NO₂ concentration over Europe originate from continental scale anthropogenic sources,
• 2.(b) 15% of precipitation sulfate and 11% of precipitation nitrate over Europe are contributed by hemispheric background,
• 3.(c) hemispheric background pollution values for Europe were found as 1.25 μg (SO₂-S)m⁻³, 0.80 μg (SO₄²⁻-S)m⁻³, 0.157 mg (SO₄²⁻-S)l⁻¹ and 0.04 mg (NO₃⁻-N)ℓ⁻¹.

     

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.     

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.     

Chance-constrained/stochastic linear programming model for acid rain abatement—II. Limited colinearity

In Part I of this work, a deterministic model for development of acid rain abatement strategies was extended to a stochastic form through the incorporation of uncertainty in the transfer coefficients which describe long-range pollutant transport and transformation. The two extreme cases of:

• 1.(i) complete dependence between transfer coefficients (i.e. colinearity);
• 2.(ii) complete independence (noncolinearity) were developed.

In this work, a more realistic ‘middle ground’ between these two extremes is investigated. This approach and its associated transfer coefficient covariance structure involve limited colinearity. A simplified linear version of the limited colinearity optimization model is employed. An application is presented which shows that a central three-state, one-receptor sub-system (‘sub-airshed’) in eastern North America plays a dominant role with respect to determining overall system performance characteristics. Nonlinear, nonlinearnonseparable and multiobjective extensions of the stochastic model are discussed.     

Gaussian versus top-hat profile assumptions in integral plume models

Numerous integral models describing the behaviour of buoyant plumes released into stratified crossflows have been presented in the literature. One of the differences between these models is the form assumed for the self-similar profile: some models assume a top-hat form while others assume a Gaussian. The differences between these two approaches are evaluated by

• 1.(a) comparing the governing equations on which Gaussian and top-hat models are based;
• 2.(b) comparing some typical plume predictions generated by each type of model over a range of model parameters.

It is shown that, while the profile assumption does lead to differences in the equations which govern plume variables, the effects of these differences on actual plume predictions is small over the range of parameters of practical interest. Since the predictions of Gaussian and top-hat models are essentially equivalent, it can thus be concluded that the additional physical information incorporated into a Gaussian formulation plays only a minor role in mean plume behaviour, and that the tophat approach, which requires the numerical solution of a simpler set of equations, is adequate for most situations where an integral approach would be used.     

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.

     

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.     

Effects of studded tires on roadside airborne dust pollution in Niigata,Japan

Two series of dust samples, collected by Andersen impactors (denoted by AN) and low-volume air samplers (denoted by LV), were investigated with respect to roadside airborne dusts collected in two different periods in 1983. These were the periods

• 1.(i) with studded tires (February and March) and
• 2.(ii) without studded tires (October).

Multi-element determinations of these samples were made by neutron activation analysis and atomic absorption spectrometry. The total concentration of AN in roadside air for period (i) was about three times higher than for the period without studded tires. The lithophilic elements such as Na, Al, K, Ca, Ti, Fe and Th, and component-metal elements of stud tip, W and Ta, produced a significant increase in atmospheric concentration in winter. The contribution of pavement material, one of the most interesting components of airborne particles in this study, was related to total AN and LV by the chemical element balance method. It made up only 16 percent (9.1 μgm⁻³) of AN in October, compared with 46 percent (70.2 μgm⁻³) in February. It was also observed that the atmospheric concentrations of pavement debris to total LV decreased with the distance from the road to each sampling site.