Is it Advection? Convection?

Jan 2, 2019

Environmental Enlightenment #118

About 80 percent of the entries in any English dictionary are borrowed, mainly from Latin. Over 60 percent of all English words have Greek or Latin roots. In the vocabulary of the sciences and technology, the figure rises to over 90 percent. (Ref.

“Ad” in Latin means “toward”, and “vection” comes from “vehere” meaning, to carry. Put them together and we get “advection.”

The concept of Advection is that something is being carried forward by the movement of something else. It is a technical term.

If we stretch it non-technically, we can say that the transport of people by train is “advection.”

In meteorology, advection is the horizontal transfer of any atmospheric property (hot air, cold air, moist air, etc.) by the wind.

Advection Fog in San Francisco

“Con-“ in Latin is “together,” and “vection” derives from “vehere” meaning to carry. Stitch them together and we have “convection.”

The basic concept of Convection is that when you suspend heavy and light particles together, the lighter particles move up and heavier particles sink down.

A non-technical illustration of the concept might be a human pyramid.

Technically, Convection is the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity.

For a live demonstration, watch the video to the right.

Volatile organic chemicals (VOCs) can be emitted from contaminated soil or groundwater and intrude overlying buildings, impacting the quality of indoor air.

The illustration below depicts toxic vapors carried under the building by convection.

Heating, ventilation and air conditioning systems (“HVAC” systems), basements, strong winds and other factors can exacerbate vapor intrusion problems by reducing internal air pressure and creating a “vacuum effect” that enhances the advective flow (flow by advection) of vapors through building floors.

The field of vapor intrusion investigations is still evolving

Acknowledgment: “ Screening For Environmental Concerns At Sites With Contaminated Soil and Groundwater; INTERIM FINAL – February 2005;” California Regional Water Quality Control Board, San Francisco Bay Region, Oakland, California.


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