urban meteorology i october 10, 2007. urban meteorology special concerns –severe weather –air...
TRANSCRIPT
Air Pollutants
• Air pollutants – airborne substances (solid, liquid, or gas) that occur in concentrations high enough to threaten the health of people and animals.
• Come from natural and anthropogenic sources
• Natural sources – wind, volcanoes, forest fires
Air Pollutants
• Antropogenic pollution is from fixed and mobile sources
• Pollution is either primary or secondary air pollution– Primary enters the atmosphere directly:
smokestack, tail pipes– Secondary forms when a chemical reaction
occurs between a primary pollutant and the air or sun
Particulate Matter Pollution
• The most visible type of pollution in the atmosphere
• Natural and anthropogenic
• Particulates are particles of dust, soot, sulfuric acid, PCBs, asbestos, and ash that are small enough to be suspended in the air
Particulate Matter Pollution
• Particulate are hygroscopic, so water vapor is attracted to them in the atmosphere
• This creates a wet haze in the atmosphere – water vapor condensing around particulates, scattering sunlight, and giving the sky a milky appearance
Carbon Monoxide
• The most plentiful of the primary pollutants
• Produced by the incomplete combustion of carbon
• Thanks to Clean Air laws, has been reduced by 40% since 1970
• Removed from the air naturally by soil microbes (which there aren’t many of in cities)
Carbon Monoxide Pollution
• Why is it a problem?
• In areas with poor ventilation (parking garage, cities with inversion layers close to the surface, valley bottoms), carbon monoxide collects
• Human hemoglobin prefers carbon monoxide to oxygen
• Leads to brain suffocation
Smog
• Smog = smoke + fog
• Large cities experience photochemical smog = smog + sunlight– aka Los Angeles-type smog
• When smog is sulfurous, its London-type smog– Certain types of coal have more sulfur than
other types
Ozone
• Troposheric ozone is BAD!!!– Secondary pollutant– Nitrogen dioxide + sunlight = nitric oxide and
atomic oxygen– Atomic oxygen + oxygen = ozone– Ozone production is higher during the
summer months and in the afternoon when there is sunlight
• Peak between 2 and 4 pm
Air Quality Index
• Includes carbon monoxide, sulfur dioxide, nitrogen dioxide, ozone, and particulates
• Amounts of primary pollutants has decreased
• Harder to decrease secondary pollutants
Air Pollution
• Factors affecting air pollution– Wind– Inversions
• Stable vs unstable• Height of smoke stacks• Radiation inversion – night and early morning• Subsidence inversion – long-lived
– Topography • Inversion created by and pollution trapped in
valleys
Ingredients for Pollution Buildup
• Many sources of air pollution in a small space (like a valley or basin)
• High pressure cell
• Light or absent surface winds
• Subsidence inversion
• Clear skies to promote radiation inversion
• Sunlight
Urban Heat Islands
• More pronounced at night
• Causes thermal low to set up over cities
• Country breeze flows into city from suburbs into the low
• If no inversion present, increases the likelihood of precipitation
Urban Heat Islands
• Humid cities have more rainfall than the surrounding countryside
• Areas downwind from humid cities have increased rainfall, particularly during weekdays
• Caused by increase of airborne pollutants that serve as condensation nuclei
Urban Heat Islands
• Reasons– Pavement absorbs more heat than soil or
plants – releases it slowly at night making cities warmer
– Buildings create urban canyons that disrupts air flow and movement of pollutants
– Pollutants can either trap or block radiation– Excess water vapor produced
Urban Heat Islands
• Change surface air flow – Causes air to flow into cities from the
countryside– If water body nearby, water vapor pulled into
the cities– Atlanta is 5-8ºF warmer than the surrounding
countryside