Glossary of Scientific Units



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Glossary of Scientific Units

Temperature Units:
Degrees Celsius (°C): Introduced by a Swedish astronomer, Andres Celsius, 1°C is defined as 1/100 of the temperature difference between water freezing point and boiling point by a pressure of 1 atmosphere. The thermometer freezing point is 0° and the boiling point is 100°.

Degrees Fahrenheit (°F): Named for the German-born scientist, Gabriel Daniel Fahrenheit, 1 °F is defined as 1/180 of the temperature difference between water freezing point and boiling point. The thermometer freezing point is 32° and the boiling point is 212°.

Degrees Kelvin (°K): Invented by William Thomson, Lord Kelvin, a 19th Century British scientist, this scale is based upon the fact that the coldest it can get (theoretically) is -273.15 degrees Celsius. The value, -273.15 degrees Celsius, is called "absolute zero." At this temperature it is thought that molecular motion stops. Since it cannot get any colder than –273.15 °C, the Kelvin scale uses this number as zero. Its unit, the degree Kelvin, is equal to the degree Celsius.

Conversion Equations:


  1. To convert Fahrenheit to Celsius use:


    Celsius = (Fahrenheit – 32) * 5/9

  2. To convert Celsius to Fahrenheit use:


    Fahrenheit = (Celsius * 9/5) +32

  3. To convert Celsius to Kelvin use:


    Kelvin = Celsius + 273






Time Units:
bp: (years) before present

kbp: thousands of years before present

mbp: millions of years before present

Concentration Units:
For very small concentrations of gases, atmospheric scientists use the following units:

ppmv: parts per million (106) by volume; the fraction of volume of gas occupied by a component multiplied by 1,000,000. If there is 3 ppm of CO2 in a bottle filled with gas, then for every 1,000,000 molecules in the bottle, 3 of those molecules are CO2.

ppbv: parts per billion (109) by volume; the fraction of volume of gas occupied by a component multiplied by 1,000,000,000. If there is 3 ppb of CO2 in a bottle filled with gas, then for every 1,000,000,000 molecules in the bottle, 3 molecules of those are CO2.

pptv: parts per trillion (1012) by volume; the fraction of volume of gas occupied by a component multiplied by 1,000,000,000,000. If there is 3 ppt of CO2 in a bottle filled with gas, then for every 1,000,000,000,000 molecules in the bottle, 3 of those molecules are CO2.

Mass Units:
When dealing with the enormous quantities of carbon discussed in global climate change studies, scientists use the following units:

tonne: a unit of weight equal to 1000 kg (103 kg).

kt: kilotonnes; equal to 1000 tonnes or 106 kg.

GtC: gigatonnes of carbon; 1 GtC is equal to 109 tonnes of carbon or 1012 kg. 3.7 Gt carbon dioxide will give 1 GtC. To give you an idea how big this unit is: in 1997 the total supply of petroleum for the USA (including imports) was approximately 1 Gt per year.

TgC: teragrams of carbon or 1012 grams of carbon.

PgC: petagrams of carbon or 1015 grams of carbon; 1 PgC is equal to 1 Gigatonne of carbon.
Scientific Notation:

Fraction


Prefix

Symbol

Multiple

Prefix

Symbol

10-1

deci

d

10

decca

da

10-2

cent

c

102

hecto

h

10-3

milli

m

103

kilo

k

10-6

micro



106

mega

M

10-9

nano

n

109

giga

G

10-12

pico

p

1012

tera

T

10-15

femto

f

1015

peta

P

10-18

atto

a












Some Chemical Symbols:



O2: molecular oxygen

O3: ozone

N2: molecular nitrogen

N2O: nitrous oxide

NO: nitric oxide


NO3: nitrate radical

NOx: Sum of NO and NO2

NO3- : nitrate ion

HNO3: nitric acid

NH3: ammonia

NH4+ : ammonium ion

H2: molecular hydrogen

H2O: water

OH: hydroxyl

HO2: hydroperoxyl

HOx: the sum OH and HO2

C: carbon; there are 3 isotopes: 12C, 13C, 14C

CO: carbon monoxide

CO2: carbon dioxide

F2: molecular fluorine

Cl2: molecular chlorine

Br2: molecular bromine

CFC: chlorofluorocarbon

CFC-11: CFCl3 or trichlorofluoromethane

CFC-12: CF2Cl2 or dichlorodifluoromethane

CFC-113: C2F3Cl2 or trichlorotrifluoroethane

CFC-114: C2F4Cl2 or dichlorotetrafluoroethane

CFC-115: C2F5Cl or chloropentafluoroethane

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