Direct and Indirect Measurements

Direct sampling

• In situ. Actually, in the studied place.

Reliable and the best option because of the exact results gases
It is difficult to carry all of the instruments

• Ex situ. Off from the place where sample is established

Use of more methods and instruments, flexible
You cannot experiment instantly and so the sample could suffer some changes.
Shipping and handling is necessary.
When measuring pollution, direct measurements could be use to measure the concentration of:

• gases
• particulate matter
• pH
• dissolved oxygen
• biomass content
• salts
• conductivity
• turbidly

Most of the measurements are giving in units per area, or per
Indirect sample
These measurements are the ones where we measure one factor in order to study or get conclusions for other factor. They don’t really tell you the concentration, you need to interpret them.
Examples of it are

• Indicator species,  They define an specific area or a specific biome
• Biodiversity indexes
• Chromatography
• Spectroscopy