Pollutant concentration estimation

In these types of control strategies, emission limits should be based on ambient pollutant concentration estimates for the averaging time that results in the most stringent control requirements. In all cases, these concentration estimates are assumed to be the sum of the pollutant concentrations contributed by the source and an appropriate background concentration. An air quality model is used to determine which averaging time (e.g., annual, 24-hour, 8-hour, 3-hour, 1-hour) results in the highest ambient impact. For... 

The physical state of a pollutant is obviously important a particulate coUector cannot remove vapor. Pollutant concentration and carrier gas quantity ate necessary to estimate coUector si2e and requited efficiency and knowledge of a poUutant s chemistry may suggest alternative approaches to treatment. Emission standards may set coUection efficiency, but specific regulations do not exist for many trace emissions. In such cases emission targets must be set by dose—exposure time relationships obtained from effects on vegetation, animals, and humans. With such information, a Ust of possible treatment methods can be made (see Table 1). 

The initial direction of transport of pollutants from their source is determined by the wind direction at the source. Air pollutant concentrations from point sources are probably more sensitive to wind direction than any other parameter. If the wind is blowing directly toward a receptor (a location receiving transported pollutants), a shift in direction of as little as 5° (the approximate accuracy of a wind direction measurement) causes concentrations at the receptor to drop about 10% under unstable conditions, about 50% under neutral conditions, and about 90% under stable conditions. The direction of plume transport is very important in source impact assessment where there are sensitive receptors or two or more sources and in trying to assess the performance of a model through comparison of measured air quality with model estimates. 

First order parameters affecting dispersion stem from meteorological conditions. These, as much as any other consideration, determine how a stack is to be designed for air pollution control purposes. Since the operant transport mechanisms are determined by the micro-meteorological conditions, any attempt to predict ground-level pollutant concentrations is dependent on a reasonable estimate of the convective and dispersive potential of the local air. The following are meteorological conditions which need to be determined ... 

Chapter 5 describes simplified methods of estimating airborne pollutant concentration distributions associated with stationary emission sources. There are sophisticated models available to predict and to assist in evaluating the impact of pollutants on the environment and to sensitive receptors such as populated areas. In this chapter we will explore the basic principles behind dispersion models and then apply a simplified model that has been developed by EPA to analyzing air dispersion problems. There are practice and study problems at the end of this chapter. A screening model for air dispersion impact assessments called SCREEN, developed by USEPA is highlighted in this chapter, and the reader is provided with details on how to download the software and apply it. 

Buildings are ventilated mechanically with the ITVAC systems where it is a controlled process, as well as via air infiltration and through the openable windows and doors where it is largely an uncontrolled process. However, as discussed earlier, mechanical ventilation is one of the most energy-intensive methods of reducing indoor pollutant concentrations primarily because of the need to thermally condition air before it can be circulated inside the occupied spaces. It is estimated that the... 

Baughman GL, Lassiter RR. 1978. Prediction of environmental pollutant concentration. In Carins J Jr, Dickson KL, Maxi AW, eds. Estimating the hazard of chemical substances to aquatic life. American Society for Testing and Materials, Philadelphia, PA. ASTM STP657, 35-54. 

More generally, the loss function need not be symmetric L(e) L(-e). Indeed, underestimation of a pollutant concentration may lead to not cleaning a hazardous area with the resulting health hazards. These health hazards may be weighted more than the costs of cleaning unduly due to an overestlmatlon of the pollutant concentration. The optimal estimators linked to asymmetric linear loss functions are given In Journel (3 ). 

Assessment of spatial distributions of pollutant concentrations is a very specific problem that requires more than blind mapping of these concentrations. Not only must the criterion of estimation be chosen carefully to allow zooming on the most critical values (the high concentrations), but also the evaluation of the potential error of estimation calls for a much more meaningful characteristic than the traditional estimation variance. Finally, the risks a and p of making wrong decisions on whether to clean or not must be assessed. 

Concentration estimate and associated probability, Isopleth maps, 115f Conditional distribution approach, assessment of spatial distributions of pollutants, 112-14 Conditional distribution of... 

Receptor Exposure. Exposure modeling should produce a statistically representative profile of pollutant intake by a set of receptors. This is done by combining the space/time distribution of pollutant concentrations with that of receptor populations (whether they be people, fish, ducks or property made of some material that is vulnerable to pollutant damage). The accuracy and resolution of the exposure estimates are chosen to be consistent with the main purposes of decision making. These purposes include the following ... 

A variety of modeling approaches may be used to estimate pollutant concentrations in exposure media. These range from qualitative estimates extrapolated from case examples or environmental scenarios, simple analytical equilibrium or transport models, to complex multi-media models. In selecting an approach or approaches, it is important that ... 

Modeling pollutant concentration between source and worker prediction of small-scale dispersion of contaminants using data collected with a high-resolution three-axis sonic anemometer. The ultimate goal is to convert information collected by the anemometer into eddy diffusion coefficients, which can be used to estimate contaminant concentrations at any point within indoor environments. 

A full discussion of these models will follow in Section 21.3. At this point we will deal only with a special version of Eq. 21-30 in which there is no back-reaction from B to A and no external input of chemical B. As an example imagine the case of the pollution of a pond by a pesticide A that in the water is transformed into another compound B that is more toxic than the original compound. For instance, thiophos-phoric acid ester is transformed to the corresponding phosphoric acid ester (see Chapters 2 and 13). Then it would be important to predict the maximum concentrations of A and B in the pond and to estimate the necessary time until the pollutant concentration has fallen below a certain threshold. Such a case will be discussed in Illustrative Example 21.4 below. 

This chapter will focus on PM ambient concentrations, which are key variables for exposure models, and are generally obtained by direct measurements in air quality monitoring stations. However, depending on the location and dimension of the region to be studied, monitoring data could not be sufficient to characterise PM levels or to perform population exposure estimations. Numerical models complement and improve the information provided by measured concentration data. These models simulate the changes of pollutant concentrations in the air using a set of mathematical equations that translate the chemical and physical processes in the atmosphere. 

Exposure to VOCs in public beauty shops can also be high. Many cosmetic products contain VOCs such as 2-phenoxyethanol, 2-butanone, acetone, terpenes, 2-hydroxy-4-methoxy-benzophenone or phenylmethanol. In particular, hair sprays are potential sources of indoor pollutants. To estimate VOC concentrations associated with the use of beauty products, a female subject was placed in the model room described earlier and sprayed with 16.1 g hair lacquer. Propellant gases (butane, pentane), ethanol, limonene and tripropyleneglycol (isomers) were subsequently monitored in the room. Thirty minutes after the application of this product, the highest VOC concentrations were measured for ethanol (>100pg/m3)... 

The influence of emission of some airborne pollutants on an agricultural area has to be investigated. From an area of 10000 square meters, ten soil samples were taken from the surface soil horizon. 1 g of each sample was recently analyzed in the laboratory. This means that the results, for instance a pollutant concentration, obtained from ten 1 g samples are used to estimate the level of pollution in the whole area with a medium depth of the surface horizon of 30 cm and a medium soil density of 1.5 g cm-3. A parent population of more than 109 g has to be assessed from a total sample mass of 10 g The necessity of extrapolation over a range of several orders of magnitude indicates the problems connected with sampling process. 

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