Lecture 5

Lecture 5 - Air AirPollution Thestorycontinues 1 The...

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ir Pollution Air Pollution The story continues… 1
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e Role of Topography The Role of Topography t night, cold air tends to drain downhill settling in low At night, cold air tends to drain downhill settling in low lying areas and valleys Can strengthen existing inversions Can transport pollutants downhill Source: Ahrens, 2003 2
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ountry Breeze Country Breeze Thermally induced low pressure centre over the city Induces a convection cell which brings air in from surrounding rural area industry is located outside city pollutants could be drawn in If industry is located outside city, pollutants could be drawn in Source: Ahrens, 2003 3
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Sea Breeze 4
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s Angeles inversion and pollution Los Angeles inversion and pollution 5
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onora, 1948 Donora, 1948 6
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ssessing Pollution Assessing Pollution ollution Potential Pollution Potential Probability for a high level of pollution in a given area if pollution sources were present Soiling Index Measure of actual pollution levels experienced in a certain region Terms used when assessing air quality in an urban nvironment or in “impact assessment” for planned environment or in impact assessment for planned industrial complexes 7
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e Box Model The Box Model nderstanding pollution potential: Understanding pollution potential: ixed layer or h Mixed layer or Boundary Layer U Wind speed ‘U’ C y Sources ‘S’ x 8
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ass Balance Mass Balance se a simple mass balance with the box Use a simple mass balance with the box model: put of pollutants from sources (S per unit area) Input of pollutants from sources (S per unit area) into box = Sxy (kgs 1 ) ollutant output blown from the box by wind (u) is Pollutant output blown from the box by wind (u) is given by product of volume per unit time and concentration = yhuC (kgs 1 ) Assuming steady state conditions (no change with time) these must be equal: Sxy = yhuC 9
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ass Balance Mass Balance lve for the concentration ‘C’: Solve for the concentration C: Sx = yy h u C • ‘hu’ is called the “ventilation coefficient” ¾ higher means lower pollution concentration (air is better mixed above the source region) e inverse of the ventilation coefficient is the pollution ¾ the inverse of the ventilation coefficient is the pollution potential ¾ PP = 1 / (hu) 10
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Hell is a city much like London – a populous and smoky city (P.B. Shelley–written during the early part of the industrial revolution) 11
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og Smog “ ondon pe” London type In London, smoke from coal combustion (SO 2 ) ixed with fog from the North Sea mixed with fog from the North Sea Resulted in extreme reduction in visibility, sulfurous odours, and occasionally, illness and death “Smog” = smoke + fog Gray in colour 12
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rban air quality Urban air quality “ ondon was this day involved, for several hours, in London was this day involved, for several hours, in palpable darkness… Such is, occasionally, the effect of the accumulation of smoke between
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Lecture 5 - Air AirPollution Thestorycontinues 1 The...

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