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Air Pollution Orientation

US EPA APTI Course 422

July 12, 2006Kabul, Afghanistan

Masud Karim, Ph.D., P. Eng.

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Course Modules

Four modules: Air Pollution Air Pollution Control Emission Control Technologies Air Quality Management System

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3. CONTROL TECHNOLOGIES

Factors that influence the transport and dispersion of pollutants

Dispersion modeling The ambient air monitoring program Principles of sampling and analysis of pollutants Emission inventories Equipment, processes and actions; Types of compliance and enforcement strategies.

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Transport & Dispersion of Air Pollutants

Transport and dispersion are influenced by many complex factors. Global and regional weather patterns, local topographical conditions affect the way

that pollutants are transported and dispersed. wind speed and directionAtmospheric stability: Atmospheric stability

refers to the vertical motion of the atmosphere.Higher the wind speed, the lower the pollutant

concentration

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Temperature Inversion

Wind is the natural horizontal motion

Wind occurs when warm air rises, and cool air comes in to take its place.

Wind is caused by differences in pressure in the atmosphere.

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Plume

The visible flow of pollutants from a stack is referred to as the plume.

The shape of the plume is affected by stack height, velocity and the buoyancy of the gases, and immediate surroundings.

Heat energy is added to the stack gases to increase the height of the plume.

Plume will disperse more before it reaches ground level.

An inversion can prevent the rise and dispersal of pollutants from the lower layers of the atmosphere and cause a localized air pollution

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Dispersion Modelling

Dispersion modeling is a method for estimating ground-level concentration of pollutants at various distances from a source.

Modeling refers to a general technique that uses mathematical representations of the factors affecting pollutant dispersion.

Computers are used extensively to help scientists model the complex systems responsible for transport and dispersion of air pollutants.

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Modeling Parameters

The following parameters are required for modelling: location of the emission point (latitude and

longitude), the quantity and type of pollutants emitted, stack gas conditions, the height of the stack, and meteorological factors that include wind speed,

ambient temperature profiles, and atmospheric pressure.

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Selection of Model

Selection of an air quality model for a particular air quality analysis is dependent on the type of pollutants being emitted,

the complexity of the source, and the type of topography surrounding the

facility. Common modeling systems used are the

SCREEN model, Industrial Source Complex model (ISC), and AERMOD.

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Dispersion Models: SCREEN

SCREEN can model single source, short-term calculations, including estimating maximum ground-level concentrations and the distance to the maximum, incorporating the effects of building downwash on the maximum concentrations for both the near wake and far wake regions.

The SCREEN model can also be used to model the effects of simple volume sources using a virtual point source procedure.

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Dispersion Model: ISC

ISC model can be used to assess pollutant concentrations from a wide variety of sources associated with an industrial complex up to a distance of 50 kilometers.

In addition to concentrations, it can estimate deposition rates and is appropriate for simple and complex terrain.

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Dispersion Model: AERMOD

AERMOD is a steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain.

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Dispersion Model

Dispersion modeling is used for two major reasons: modeling can predict pollutant

concentration estimates at most locations where there are no air monitors and models can predict the potential impact of

new sources before they are built as well as how new pollution control devices will affect the outcome of the pollutant.

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Air Quality Monitoring

Ambient air monitoring networks: inform the public of air quality levels and

exposure establish the compliance status of cities and

other areas track air quality trends and evaluate

progress of emission control programs support development of emission control

and air quality research programs

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Air Quality Monitoring: PM

Particulate monitoring is usually accomplished with manual measurements and subsequent laboratory analysisGravimetric analysis refers to the quantitative

chemical analysis of weighing a sample Atomic Absorption Spectrometry (AAS) is

used for the determination of single elements in analytical samples.

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Methods of Measuring Pollutants

Spectrophotometry: Measures the amount of light that a sample absorbs. The amount of light absorbed indicates the amount of analyte present in the sample. SO2 and O3 are measured using this method.

Fourier Transform Infrared Spectroscopy (FTIR): Sample absorbs infrared radiation and difference in absorption is measured. CO, VOC, CH4 are measured using this method.

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Methods of Measuring Pollutants

Chemiluminescence: Based upon the emission spectrum of an excited species that is formed in the course of a chemical reaction. NO2 and O3 are measured using this method.

Gas chromatography (GC) - Responds in proportion to number of carbon atoms in gas sample.VOC is measured using this method.

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Emission Inventories Emissions inventory is a quantitative list of

the amounts and types of pollutants that are entering the air from all sources within a certain area.

Elements in an emission inventory are the characteristics and locations of the sources, as well as the amounts and types of pollutants emitted.

Emission inventory can help identify air pollution concerns and determine air quality goals that a certain region needs to meet.

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Source Control Technology: PM

Control techniques for particles focus on capturing the particles emitted by a source.

Particles are collected and channeled through a duct or stack.

Choice of a control device is depend on particle sizes, exhaust flow rate, temperature, moisture content, etc.

Common control devices are: electrostatic precipitators, fabric filters, venture scrubbers, cyclones, and settling chambers.

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Control of gaseous pollutants from stationary sources

Common method for controlling gaseous pollutants is the addition of add-on control devices to recover or destroy a pollutant.

Four commonly used control technologies for gaseous pollutants: absorption, adsorption, condensation, and incineration (combustion).

The choice of control technology depends on the pollutant that must be removed.

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Control of Pollutants from Mobile Sources

Mobile source emission control requires an integrated approach. This approach includes: technological advances in vehicle and

engine design together with cleaner, high-quality fuels,the addition of vapor and particulate recovery

systems and development of auto I/M programs.

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Enforcement

State Implementation PlanCompliance monitoringAir Quality PermitActions taken in response to violations

of environmental law or regulations by a person or company.