MODEL DISPERSI PENCEMAR UDARA PDF

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MODEL DISPERSI PENCEMAR UDARA Abdu F. Assomadi Main concepts in air quality modeling 2 Parameter-parameter dalam Model  Sumber (Karakteristik emisi) laju emisi (massa/waktu) lokasi sumber (koordinat) temperatur gas emisi (K) tinggi plume rise (m)  Meteorology Temperatur Atmosfer Stabilitas Atmosfe...

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MODEL DISPERSI PENCEMAR UDARA Abdu F. Assomadi

Main concepts in air quality modeling

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Parameter-parameter dalam Model 

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Sumber (Karakteristik emisi) laju emisi (massa/waktu) lokasi sumber (koordinat) temperatur gas emisi (K) tinggi plume rise (m) Meteorology Temperatur Atmosfer Stabilitas Atmosfer (diperlukan untuk menentukan koefisien dispersi) Kecepatan dan arah angin, turbulensi Sifat Kimia Atmosfer Reaksi-reaksi kimia di atmosfer Deposisi (basah / kering) Parameter permukaan geometri permukaan, kekasaran/terrain, lautan, daerah kota atau desa

Beberapa Model Kualitas Udara 

Model point source

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Model at urban and large scale

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Model Fotokimia

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Model-model lain:

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Model secara meteorologi

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Model plume rise dan Model Dispersi

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Model Statistik - Model Penerima/receptor di ambien

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Model deposisi

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Model bau/odor

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Model partikulat

Model Point Source 

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Model pertama yang dikembangkan untuk kualitas udara (contoh, Sutton, 1932, Bosanquet, 1936) menjelaskan sifat dispersi plume yang diemisikan dari cerobong industri. Dalam sejarahnya dinilai sukses, dari sini dikembangkan model dispersi sederhana – Model Plume Gaussian. Model ini telah diaplikasikan untuk menghitung impact plume pada MGL (max ground level) dan jarak maksimum dari sumber.

X

Z Plume Boundary

Q u Y H

The simplest dispersion modeling – Gaussian approximation for the plume spread

Not applicable to regional scales – complex terrain, convective conditions, and ground-level sources. 7

Gambaran Model Gaussian

Asumsi-asumsi pada Model Dispersi Gauss •

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Plume disebar mengikuti sebaran gauss normal baik dalam bidang horisontal maupun vertikal, dengan deviasi standar konsentrasi plume pada arah horisontal dan vertikal y, and z; Laju emisi polutan seragam, Q;

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Kondisi plume pada ground (z=0) dianggap secara total direfleksikan oleh permukaan; dan

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Plume bergerak downstream (horisontal pada arah x) dengan rata-rata kecepatan angin, u,

Limitations of Gaussian-plume models 

Causality effects Gaussian-plume models assume pollutant material is transported in a straight line instantly (like a beam of light) to receptors that may be several hours or more in transport time away from the source.

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Low wind speeds Gaussian-plume models 'break down' during low wind speed or calm conditions due to the inverse wind speed dependence of the steady-state plume equation, and this limits their application.

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Straight-line trajectories In moderate terrain areas, these models will typically overestimate terrain impingement effects during stable conditions because they do not account for turning or rising wind caused by the terrain itself. CTDM and SCREEN are designed to address this issue.

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Spatially uniform meteorological conditions Gaussian steady-state models have to assume that the atmosphere is uniform across the entire modelling domain, and that transport and dispersion conditions exist unchanged long enough for the material to reach the receptor.

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Convective conditions are one example of a non-uniform meteorological state that Gaussianplume models cannot emulate.

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No memory of previous hour's emissions In calculating each hour's ground-level concentration the plume model has no memory of the contaminants released during the previous hour(s). 10

Wark & Warner, “Air Pollution: Its Origin & Control”

TRAPPED BY MIXED LAYER

Mixed layer

Sistem Koordinat Model Dispersi Gauss 

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Short term model, steady-state Gaussian plume equation  untuk sumber kontinyu dan punya elevasi tertentu. Koordinat asal (0,0)  ditempatkan pada ground surface tepat di dasar stack. Sumbu X positif pada arah angin (downwind direction), sumbu y tegak lurus arah angin (crosswind searah sumbu X) dan sumbu Z merupakan arah vertikal. Lokasi penerima dikonversi dari sistem koordinat sumber, untuk perhitungan konsentrasi jangka waktu tertentu (sesuai arah angin dominan)

Sistem Koordinat Distribusi Gauss Arah Horizontal dan Vertikal

Persamaan Model Dispersi Gauss  

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Model Gauss  distribusi konsentrasi Rumus menghitung C gas atau aerosol (> initial momentum Forced plume: Initial buoyancy ~ initial momentum Jet: Initial buoyancy...