Air Pollution Flashcards

Flashcards on Air Pollution based on lecture notes

Learning Outcomes

Key factors affecting the transport and dispersion of air pollutants; causes and health impacts of historical air pollution episodes.

Trilogy of Air Pollution

Natural and human-generated emissions, winds, transport and chemical reactions.

Important factors in Dispersion

Sources, Transport, Receptors + Topography + Meteorology

Wind Direction

From where it is blowing to where it goes and what has been collected before it reaches us. Identified with one of 16 or 32 points of the compass. More scientifically, as an angle in degrees clockwise from north.

Wind Speed (ws)

ms-1 or knots (1 knot = 1 nautical mile/hour; 1 nautical mile = 6080 feet, or 1.15 statute miles). Important for atmospheric dispersion.

Atmospheric Stability

Vertical movement of air is strongly influenced by the stability of the atmosphere and can be assessed by measuring the vertical temperature profile of the atmosphere. The rate of change of temperature with altitude.

Environmental lapse rate (ELR)

Change of temperature with height for a specific measured location

Dry adiabatic lapse rate (DALR)

The air is assumed to be dry, behave adiabatically with the surrounding atmosphere, and have a lapse rate of -9.8oC/km.

Stability classes

Neutral, Unstable, Stable.

Low pressure system

Created when air that is warmed by surface heating begin to rise

High pressure system

Created when air is descending to the ground

Differential Heating

Everything on earth absorbs, stores and reradiates the sun's energy. Some part of the earth, or different surfaces heat more readily than others.

Conduction

Transfer of heat when touches a heated surface.

Convection

Vertical mixing of the air.

Atmospheric Stability - UNSTABLE

Atmospheric temperature (ELR) changes less dramatically with altitude than temperature of the air parcel (DALR) that contains the pollutants. Enhance mixing. Enhanced dispersion of pollutants. Lowered pollutants concentrations

Atmospheric Stability - NEUTRAL

Exerts no force on pollutant emissions that move vertically. Occurs when the temperature changes for the atmosphere and the air parcel containing the pollutants are nearly identical

Atmospheric Stability - STABLE

Atmospheric temperature (ELR) changes more dramatically with altitude than temperature of the air parcel (DALR) that contains the pollutants. Less vertical mixing. Less dilution

Inversions

Condition when air temperature increases with height.

Ground based inversion

Occur when temperature increases with height beginning at the ground surface.

Elevated inversion

Formed when the temperature decreases with height from the ground to some altitude but increases above these altitudes.

TOPOGRAPHY

Representation of surface features such as mountains, hills, rivers, and valleys.

Fanning Plume

Occur in stable conditions. The inversion lapse rate discourages vertical motion without prohibiting horizontal motion and the plume may extend downwind from the source for a long distance. Often occur in the early morning.

Looping Plume

Occur in highly unstable conditions. Unstable conditions are generally favorable for pollutant dispersion, momentarily high ground-level concentrations can occur if the plume loops downward to the surface.

Coning Plume

Characteristic of neutral conditions or slightly stable conditions. It is likely to occur on cloudy days and sunny days before the development of unstable daytime condition.

Fumigation Plume

If the plume is released just below the inversion layer, a very serious air pollution episode could develop. When pollutants are released below the inversion layer, gaseous emissions quickly cool and descend to ground level.

Lofting Plume

When conditions are unstable above an inversion, the release of a plume above the inversion results in effective dispersion without noticeable effects on ground level concentration around the source.

THREE major air pollution episodes discussed

Fog disaster in Meuse Valley (1930), ‘Donora Death Fog (1948)’, ‘Big Smoke in London (1952)’

Cause of Fog disaster in Meuse Valley (1930)

Poisonous products in the waste gas of the many factories in the valley, in conjunction with unusual climatic conditions. Sulfur dioxide (SO2) or oxidation products of that compound.

Donora Death Fog (1948)

A temperature inversion coupled with foggy weather settled over a horseshoe-shaped valley along the Monongahela River near Pittsburgh. High concentrations of sulfur dioxide.

London Fog (1952)

Temperature inversion covered the Thames River Valley, trapping deadly acid aerosols in the atmosphere. Thousands of tons of black soot, tar particles, and sulfur dioxide had accumulated in the air from the heavy coal combustion.