PREDICTION AND ASSESSMENT OF IMPACTS ON THE AIR ENVIRONMENT

PREDICTION AND ASSESSMENT OF IMPACTS ON THE AIR ENVIRONMENT1

What is Air Pollution?Air Pollution can be defined as the presence in the outdoor atmosphere of one or more contaminant (pollutants) in such quantities and of such duration as may be injurious to human, plant, or animal life, or to property, or which may unreasonably interfere with the comfortable enjoyment of life or property, or the conduct of businessPossible Effects to Human HealthIt include eye irritation, headaches, and aggravation of respiratory difficulties. Plants and crops have been subjected to the undesirable consequences of air pollution including abnormal growth patterns, leaf discoloration or spotting, and death.

6 Steps Associated with Air Environment ImpactsIdentification of the types and quantities of air pollutants and of their impactsDescription of existing air quality conditionsProcurement of relevant air quality standards and regulationsImpact PredictionAssessment of impact significanceIdentification and incorporation of mitigation measures

Step 1: Identification of the Types and Quantities of Air Pollutants and of their ImpactsAn appropriate initial step when any proposed-project activity is to consider what types of air pollutant might be emitted during the construction and/or operational phases of the proposed-project activity and the quantities in which such air pollutants are expected to occur.Information should be aggregated by source type and construction and/or operational phase of the proposed project or activity, which could be used to delineate both the types and quantities of the air pollutants of concern.

Step 2: Description of Existing Air Quality ConditionsExisting air quality conditions can be described in terms of ambient air quality data, emission inventories, and meteorological information which related to atmospheric dispersion.

Compilation of Air Quality InformationAppropriate interpretation of air quality data should include consideration of historical trends, as well as information about the monitoring station. If possible it is desirable to examine the complete history of air quality for the sampling station in the particular locale.To utilize this information appropriately, one must carefully describe the characteristics of each sampling site, including any unique factors about the site, such as surrounding land usage, height of the sampling device above the ground surface, and the type and calibration history of the sampling equipment.

*Here in the Philippines we can get the information of the air quality through the DOST or PAG-ASA.*Graphical presentation of air quality information may be useful, particularly if there appear to be trends, either upward or downward, in the air quality levels of any of the air pollutants.

7Procurement of Development of Emission InventoryAn emission inventory is the filed confirmation on the quantities of air pollution from all sources in a defined geographical area entering the atmosphere in a given time period (typically a 1-yr period is used)It can be used as a baseline marker against which precious and anticipated future air pollutant emissions and their increase in the geographical study area as a result of the activity can be judged. Additionally, it can be used on a comparative context with regard to data from other nearby geographical areas.

In analyzing the potential air quality impacts of a proposed project or activity, it is necessary to consider the study area (potentially area or region of influence) associated with the air pollution emissions. The delineation of a study area can be made using the boundaries of the land associated with the project activity, or the delineation can include the larger area by considering the atmospheric dispersion patterns within the vicinity of the proposed project or activity.

8Summary of Key Meteorological DataMean annual speeds can be used as general indicators of dispersion conditions, with larger numerical values being more desirable as the signify the more rapid dispersion of air pollutants from the study area.

Any unique meteorological phenomena that occur in the area should be noted, particularly as related to the occurrence of typhoons or characteristics such as fog formation or persistence.

Sources of meteorological data for a study area can include local airports, local or states meteorological-climatological offices like PAG-ASA or DOST.

Baseline MonitoringAmbient air-quality monitoring refers to appropriate sampling and analysis to establish the ambient concentrations of specific pollutants. Targeted monitoring might be desirable in order to verify the experienced changes in air quality concentrations for those pollutants determined in the earlier steps to be of concern.

Step 3: Procurement of relevant air quality standards and regulationsThe primary sources of information on air quality standards, criteria, and policies will be the relevant local, cities and government agencies which have a mandate for overseeing the air resources of the study area.Pertinent institutional information and sources of data related to the air environment have been described earlier. Also, specific air-quality-management policies or requirements may be in existence for particular areas, and the particular requirements of such policies may need to be ascertained.Some examples of such policies are RA 8749 Philippine Clean Air Act of 1999 and RA 3931 National Water and Air Pollution Control RA 8749: Maximum limits for Sulfur Oxides Emissions

RA 8749: Emission Standards in the Exhaust Gas

Step 4: Impact PredictionAir quality impact prediction can be based on one to several approaches, including mass balances, the use of simple to detailed mathematical models, and other considerations.

Mass Balance ApproachesAir pollutant emissions from the construction and/or operational phase of a project-activity can be considered in relation to the existing emissions inventory for the study area. This approach will necessitate the development of an inventory representing a mass balance of the total air pollutant emissions from all sources for a proposed project or activity entering the atmosphere during the construction and/or operational phase.

Mass Balance ApproachesBox Model ApproachesA simple atmospheric dispersion model, called a box model, can be used to calculate the ground level concentration of specific air pollutants of concern emitted from the project activity. A box model is based on the assumption that pollutants emitted to the atmosphere are uniformly mixed in a volume, or box, of air. A box model is also based on the assumption that discharge mix completely and instantaneously with the air available for dilution and the released material is chemically stable and remains in the air.

Box Model ApproachAir Quality Dispersion Modeling ApproachesFrom a user perspective, air-quality dispersion models can be classified according to the source type, ground-level point, pollutant type, averaging times, and atmospheric reactions.The following model, known as the Pasquill model, as modified by Gifford, Is frequently used to analyze the air quality impacts of single, elevated point sources.

Air Quality Dispersion Modeling ApproachesModels can be useful in estimating the impacts of the project or activity on air quality. Also various modifications of the proposed project-activity can be evaluated to assess the effectiveness of mitigating efforts to minimize the impacts of the project-activity.

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Step 5: Assessment of Impact SignificanceSignificance assessment refers to the interpretation of the significance of anticipated changes related to the proposed project. One basis for impact assessment is public input; this input could be received through a continued scoping process or through the conduction of public meetings and/or public participation programs.

A final consideration could include the identification of specific effects of the types of air pollutants from a proposed project or activity. This may include the identification of sensitive receptors in the study area

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Step 6: Identification and Incorporation of Mitigation MeasuresMitigation measures refer to the project activity design or operational features that can be used to minimize the magnitude of the air quality impacts. The key approach is to revise the design as needed in order to reduce the air pollutants expected to be emitted from the project-activity.

Step 6: Identification and Incorporation of Mitigation MeasuresExamples of mitigation measures for reducing air pollutants emission include:Limitation on the practice of open burning of agricultural crop residuesWind erosion from open land can be controlled by using chemical stabilizers, watering, and wind breaksCommon techniques for controlling air pollution from unpaved roads are paving, surface treating with penetration chemicals, working of soil stabilization chemicals into the roadbed, watering and traffic control and regulationsFugitive-dust-control measures can be also used for open-waste piles and staging areas, dry surface impoundments, landfills, land treatment systems and waste stabilization measures.END