Air Pollution, the Automobile, and Public Health (1988) / Chapter Skim
Currently Skimming:
Mathematical Modeling of the Effect of Emission Sources on Atmospheric Pollutant Concentrations
Mathematical Modeling of the Effect of Emission Sources on Atmospheric Pollutant Concentrations
Pages 161-206
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 161... ...
, Air Pollution, the Automobile, and Public Health.
|
From page 162... ...
The second step is to accurately determine the effects that atmospheric transport and chemical reactions have on pollutant concentrations. Mathematical models are ideally suited to this task.
|
From page 163... ...
frequency; or, more generally, the magnitude c~x,tJ of the concentration as a function of the path of the subject characterized by his or her position x at all times t for the duration of the time interval in which exposure takes place. This chapter discusses how air quality models can be used to determine how c~x,tJ depends on emission sources.
|
From page 164... ...
After a model has been evaluated, it is ready for use in conducting source apportionment, population exposure, and control strategy studies, as discussed in the next section. Studies of this type are of great interest, but few comprehensive control strategy studies have been conducted using state-of-the-art air quality models.
|
From page 165... ...
. tons to particulate matter concentrations, receptor models are now widely accepted as a replacement for rollback models.
|
From page 166... ...
. It is important to realize that if the air quality model is to be an effective tool for predicting pollutant concentrations and health effects and devising strategies for controlling them, the essential characteristics of the sources must be retained within the model.
|
From page 167... ...
Empirical/statistical models, such as receptor-oriented and rollback models, are based on establishing a relationship between historically observed air quality and the corresponding emissions. The linear rollback model is simple to use and requires few data, and for those reasons has been widely used (see, for example, Barth 1970; South Coast Air Quality Management District and Southern California Association of Governments 1982~.
|
From page 168... ...
Nonreacting gases have also been tracked by receptor modeling methods (Yamartino 1983~. Receptor models compare the measured chemical composition of particulate matter concentrations at a receptor site with the chemical composition of emissions from the major sources to identify the source contributions at ambient monitor .
|
From page 169... ...
They do not rely on a detailed knowledge of the source fingerprint, aid, and can be used to refine estimates of the fingerprint. Research intended to extend the power of receptor models for source apportionment is continuing, including development of methods to integrate measurement uncertainties into the analysis, incorporation of aerosol properties other than elemental composition, and inclusion of the effect of chemical reactions on secondary aerosol formation.
|
From page 170... ...
This is the basis Mathematical Modeling of Effect of Emission Sources of the transport only and transport with linear chemistry models (which, for brevity, will be called transport models)
|
From page 171... ...
Diffusion of pollutants from a point source. Pollutant concentrations have separate Gaussian distributions in both the horizontal (y)
|
From page 172... ...
at the edges of the grid system used. Eulerian grid models produce pollutant concentration predictions throughout the entire airshed, which can be examined over successive time periods to observe the evolution of pollutant concentrations and how they are affected by transport and chemical reaction.
|
From page 173... ...
Emissions of NH3, NOx, HCs, and CO in the Los Angeles area during 1982. A spatially "ridded, time-resolved, and speciated emissions inventory is necessary for conducting air quality modeling studies involving chemically reacting compounds.
|
From page 174... ...
Statistical models generally rely on several years' worth of measurements of hourly or daily pollutant concentrations. The resolution of the input data would represent the minimum resolution of a statistical model.
|
From page 175... ...
In regions subject to photochemical smog, modeling the transport and distribution of O3 and the impact of automotive NOx emissions in street canyons needs to be addressed for two reasons: to determine population exposure to these pollutants, and to explain the difference between predicted pollutant concentrations calculated when using a grid size much larger than the size of a street canyon and observed concentrations measured by air monitoring stations that may be located within the influence of the street canyon (Nappo et al.
|
From page 176... ...
More recent models account for the variation of surface Mathematical Modeling of Effect of Emission Sources t Reference height (z,) Turbulent < fluid > Boundary > rb its layer Surface effects Flux = C(z,)
|
From page 177... ...
Research into the development of "emissions-to-fog chemistry" models is needed and would be valuable for determining source/health effects relationships in the instances where fog in urban areas may lead to compounds harmful to human health. Representation of Atmospheric Chemistry Through Chemical Mechanisms A complete description of atmospheric chemistry within an air quality model would require tracking the dynamics of many hundreds of compounds through thousands of chemical reactions.
|
From page 178... ...
This analytical technique is suited to developing and testing new chemical mechanisms. Given the importance of the chemical mechanism to the outcome of model evaluation, source apportionment, and control strategy studies, it is bothersome that the predictions of different chemical mechanisms do not always agree.
|
From page 179... ...
Research into the development of new chemical mechanisms is essential to advancing the accuracy and scope of air quality model predictions, especially as interest grows in the effects of noncriteria pollutants. Aerosol Dynamics Indusion of a description of aerosol dynamics within air quality models is of primary importance because of the health effects associated with fine particles in the atmosphere (Schlesinger, as well as Sun, Bond, and Dahl, this volume)
|
From page 180... ...
These studies predicted aerosol mass and chemical composition, not the aerosol size distribution (that is, how the aerosol is distributed over specific size ranges)
|
From page 181... ...
Mode! Evaluation An air quality model must be tested before it can be used confidently for a specific application, such as control strategy design or source apportionment.
|
From page 182... ...
Model evaluation procedures must account for the intended model application and formulation. Some criteria have been suggested for measuring model performance (Brier 1975; Bowne 1980; American Meteorological Society 1981; Fox 1981~.
|
From page 183... ...
(Schiermeier 1978~; and a program designed to measure particulate carbon concentrations for use in an air quality model evaluation study (Gray 1986~. Studies such as these are costly, time-consuming, and significantly increase the effort required to confirm model performance.
|
From page 184... ...
Extensive model evaluation studies have been conducted for a number of models beginning with the Gaussian plume models and continuing to the state-of-the-art urban and regional photochemical, air quality models. Turner (1964)
|
From page 185... ...
Recently developed photochemical air quality models, in the Lagrangian trajectory as well as the Eulerian grid form, use more complete descriptions of atmospheric chemistry based on the condensed chemical mechanisms described in the section on Modeling Approaches for Individual Processes. Other improvements include more accurate descriptions of pollutant dry deposition, vertical transport, and more detailed input data.
|
From page 186... ...
(1974) , is used for computing photochemically reactive pollutant concentrations such as O3.
|
From page 187... ...
The ultimate goal is their use in emission control strategy and health impact studies, of which exposure and source apportionment calculations are vital components. Population Exposure Calculations Advanced air quality models are powerful tools for use in exposure studies that seek to relate health effects to individual pollutant emission sources.
|
From page 188... ...
As noted previously, receptor models are not directly suited for determining the source of secondary aerosols such as nitrates and secondary organics. According to the 1974 emissions inventory for the Los Ane;eles area (McRae and Seinfeld 1983)
|
From page 189... ...
Nonreactive, mass conservation models based on solving equation 3, including Gaussian plume models, have been used extensively for source apportionment, control strategy analysis, and source impact modeling of nonreactive pollutants such as CO, and of carbonaceous aerosol. Recently, Gray (1986)
|
From page 190... ...
At point A, the graph indicates that decreasing NOx would increase O3 formation. Analysis of the effect of emission control on the improvement in O3 air quality is further complicated by the fact that the effect of controlling two emission sources together is not necessarily equal to the incremental improvement from controlling one source added to the incremental im provement from controlling the other source separately.
|
From page 191... ...
The large data requirements and computational times make it expensive to test a large number of emission control strategies using the most advanced photochemical airshed models. Instead, realizing that the precursors of O3 and NO2 are HC and NOX, least-cost control strategies can be estimated by identifying the least-cost approach to achieving various levels of HC and NOX emissions and then using the advanced air quality models to identify the perturbed emissions level that will meet the desired air quality standard.
|
From page 192... ...
One current policy problem now awaiting completion of an advanced air quality model is that of acid deposition control. In addition to source apportionment studies, air quality models can be used to identify potential areas of research by identifying gaps in our knowledge.
|
From page 193... ...
. Indoor air quality models currently are being developed to bridge the gap, relating the pollutant concentrations indoors to outdoor air quality, indoor emissions, ventila
|
From page 194... ...
. The usual approach to indoor air quality modeling has been to apply a mass balance equation, similar to equation 5.
|
From page 195... ...
models use the large volume of data available on pollutant concentrations and use the underlying structure of a data set to separate the contribution of different emission sources to observed air quality. The most common types of receptor models use chemical mass balance and multivariate analysis techniques and have been used in a number of locations to identify and apportion source contributions at receptor sites.
|
From page 196... ...
On the other hand, development of advanced chemical mechanisms is quite possible using our present knowledge of atmospheric chemistry. Inclusion of aerosol processes within future air quality models was identified as a key area for future research, particularly because of the suspected health effects of small particles.
|
From page 197... ...
Recommendation 6, below, would lead to rapid development of a comprehensive aerosol process air quality model. The final step in constructing a system for determining source/ air quality relationships for use in exposure studies involves developing a comprehensive indoor air quality model, as described by Recommendation 9.
|
From page 198... ...
Results from indoor air quality studies that relate indoor pollutant concentrations to those out doors can be combined with similar studies on outdoor air to help develop air quality standards and conduct source-related health impact studies. MODERATE PRIORITY Recommendation 3 Dry deposition of chemically reactive air pollutants and aerosols Pollutant Deposition is an area of current research interest.
|
From page 199... ...
Outdoor deposition measurements would benefit from improved instrumentation. Recommendation 1 Receptor models such as those using chemical mass balance Receptor Modeling techniques have proven to be very convenient tools for apportion ing the contributions of sources to atmospheric particulate matter concentrations.
|
From page 200... ...
R., Kitada, T., and Peters, L K., Mathematical Modeling of Effect of Emission Sources 1986.
|
From page 201... ...
1981. Composition of source components needed for aerosol receptor models, In: Atmospheric Aerosol Source/Air Quality Relationships (E.
|
From page 202... ...
1982. Kinetics of reactions between free radicals and sur Mathematical Modeling of Effect of Emission Sources faces (aerosols)
|
From page 203... ...
1983. Comment on "Effect of nitrogen oxide emissions on ozone levels in metro politan regions," "Effect of NOX emission rates on smog formation in the California south coast air basin," and "Effect of hydrocarbon and NOX on photochemical smog formation under simulated transport conditions." Environ.
|
From page 204... ...
8:811-826. Mathematical Modeling of Effect of Emission Sources Turk, A
|
From page 205... ...
1983. Formulation and application of a hybrid source receptor model, In: Receptor Models Applied to Contemporary Pollution Problems (S.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.