Global Air Pollution and Intercontinental Transport

This page last reviewed January 24, 2017


Severe air pollution is commonly associated with population centers, areas of concentrated industry or other human activities, but air pollution does not respect economic or political boundaries as it spreads downwind. Minute concentrations of air pollutants are found all over the world. Even modest levels of industrial activity can pollute large areas of the Earth. For example, lead emitted from metal smelting in Europe during the Greek and Roman empires deposited trace concentrations in Greenland that have been found in ice cores.

The global spread of pollution cab be seen in the figure and animated video below, which shows the planetary distribution of carbon monoxide produced by burning fossil fuels or vegetation, as measured by satellite in 2000.

Click on the image or here to view animation of carbon monoxide movement

Carbon monoxide is accompanied by other combustion-related pollutants, such as smoke, soot, sulfates, and toxic materials. Present global levels of population, urban and industrial development, and vegetation burning are causing rising concentrations of air pollution to be spread throughout the Northern Hemisphere.

Key Terms

Baseline Concentrations - Observed & measured concentrations in areas where anthropogenic influences are absent
Policy Relevant Background / North American Background - Modeled concentrations in absence of any emission inventory contributions
Stratospheric Down-folding - Air parcels rich in pollution moving downwards into troposphere due to meteorology
Long-Range Anthropogenic Transport / Long-Range Global Transport - Air parcels rich in pollution moving within troposphere from east to west
Biogenic Emissions - Emissions of volatile organic carbon (VOC) from forests, savannas, and urban trees AND Emissions of soil Nitrogen Oxide emissions (NOX) AND lighting NOX
Natural Background - Modeled concentrations restricted to Biogenic Emissions and locations anthropogenic emissions would be absent
Residual Layer - Layers aloft where vertical transport up one day’s locally generated air pollutants, long-range anthropogenic transport, and/or stratospheric down-folding may create rich pollution layers above the mixing depth



  • Meteorology, as well as, anthropogenic emission inventories, is the key factor for high ozone and particulate matter episodes.
  • Topography interacting with meteorology may limit the influence of long-range anthropogenic transport and stratospheric down-folding.
  • Global pollution effects in California are most noticeable in clean air areas; high pollution days in California are due to local sources.
  • Long-Range Anthropogenic Transport (mostly Asian) pollution sources may slow future progress toward clean air in California.
  • Large dust storms from Asia's deserts hit California a few times a decade.
  • Dilute amounts of dust from Asia's deserts regularly cross the Pacific to California.
  • Smoke from biomass burning in southeast Asia and wildfires in Siberia can also reach California.
  • Asia's coal smoke, vehicle exhaust, toxics, and farm and road dust also regularly cross the Pacific.
  • Ozone from Asia's cities adds to natural " background " ozone in clean air areas of California.
  • Economic growth, though slower in the last several years, in Asia will increase emissions and pollution impacts in California.  Pollution controls may slow emission growth.
  • Climate change may facilitate pollutant movement and ozone formation, enhancing the effects of Asian pollution in California.

Global Particulate Air Pollution

The global atmospheric particle load comes from a mix of natural and human sources. Dust from Earth's great deserts mixes with dust from roads, farms, and other soil disturbance. Smoke from wildfires mixes with smoke from burning forests and grasslands as well as coal and oil. Learn more on our webpage: Global Particulate Air pollution and its Effects on California

Global Ozone

Ozone due to manmade pollution is the main irritant in "smog" but it is also a natural component of the atmosphere.  Understanding the effects of global pollution on local ozone exposure requires tracking ozone from both natural and manmade sources. Learn more on our webpage: Global Ozone and its Effects on California


If you have any questions or comments about the content of the
Global Air Pollution Transport webpages, please contact
Ash Lashgari at (916) 323-1506 .