2.5: air pollution

atmosphere: a sea of air that surrounds the earth
divided into several layers, separated from each other by abrupt changes in temperature due to differences in absorption of solar energy

layers of the atmosphere

air pollution: the presence of chemicals in the air in quantities and durations that are harmful to the environment and human health
some pollutants are natural
- natural fires
- terpenes (from forests)
- pollen (allergen)
- dust (from volcanos)

types of pollutants

primary pollutants: harmful substances emitted directly in that form
- may react with one another or with a basic air component to become secondary pollutants
conventional pollutants + pollutant criteria
- the EPA sets the National Ambient Air Quality Standards (NAAQS) which limits six major pollutants
- particulate matter (PM)
  - classified based on diameter
  - PM10: 10 micrometers or smaller
  - PM2.5: 2.5 micrometers or smaller
  - comes from wildfires, industrial activities, motor vehicles, cooking, and fuel burning
  - particles can enter the lungs, and the smallest can enter the bloodstream
  - this can cause heart attacks, strokes, and negatively impact children’s nervous systems
  - associated with ~80,000 deaths in the US
- ozone (ground level)
- nitrogen oxides (NOx)
- sulfur oxides (SOx)
- carbon monoxide (CO)
- lead

important until the mid-1900’s in industrial cities (eg. London, Donora, Pittsburg, Chicago)
now, rarely a problem in MDCs but still a problem in China, India, Eastern Europe
caused by large amounts of heavy oil and coal burnt in homes for heat and in industrial work
- generally worse in winter
releases sulfur oxides (SOx) and particulate matter
appears grey in color

the great smog

took place in London in December 1952
unusually cold → more coal burnt
visibility fell to ~12 inches
100,000+ people treated for respiratory problems
caused 3,000-4,000 extra deaths
- extra death: a death caused by smog above the normal rates which are attributed to the abnormal smog conditions
- mainly of cardiac and respiratory ailments
asthma
- disease which negatively effects lungs
- more common among people alive/born during the great smog
US equivalent: Donora, PA, October 1948

more pressing current problem in more developed countries
composed of a mixture of primary and secondary pollutants
formed when primary pollutants interact under the effect of sunlight and give origin to a mixture of 100 chemicals dominated by ozone
- worse in summer
primary pollutants involved and their sources
- nitrogen oxides (NOx) mainly from vehicles
- volatile organic compounds (VOCs) from vehicles, gas stations, dry cleaners, print shops, vegetation
appears orange in color

ozone

thermal inversion: a process which occurs when a layer of cold air temporarily trapped near the ground by a warmer, upper layer
- pollutants do not get dispersed during thermal inversions
- warm air is less dense than cold air
normal conditions
- during the day, sun warms up the air near the surface, which expands and rises, carrying low-lying pollutants higher
- under normal conditions, there is a constant movement of air
sometimes a layer of cold air is trapped beneath a warmer, less dense error
- warm air prevents ascending air currents and the dispersion of pollutants
- common in valleys and urban areas

urban heat islands

structures eg. buildings, roads, and other infrastructure absorb and re-emit the sun’s heat more than natural landscapes such as forests and water bodies
urban areas become islands of higher temperature relative to outlying areas
result in thermal inversions and more thunderstorms
dust domes: pollutants including soot trapped in urban air through thermal inversions

case study: mexico city

megacity with over 22 million people in the metro area
- more people, more industry, more cars
located at a high altitude → solar radiation is intense
surrounded by mountains, air can be stagnant with winter thermal invasions
deforestation and construction have exposed soil to wind erosion