FAQ for AMS Data Users

The purpose of this page is to serve as a repository of answers to frequently asked questions from users of AMS data products. Contributions are most welcome, and should be directed to the curator of the page (JL Jimenez as of June 2009).

What are ug sm-3?

ug sm-3 are ug m-3 converted to standard pressure and temperature (STP) conditions of 1013 mbar, 273K without any evaporation/condensation. These units are very useful when comparing data taken over a range of pressure and temperatures, such as aircraft data. They are also very useful when comparing aircraft data to data from ground sites, or data from different ground sites which have different ambient pressures and/or temperatures.

Ratios to gas-phase species (e.g. OOA/Ox) are constant when expressed in ug sm-3 ppb-1, but not if ug m-3 are used.

Note that unfortunately there are many other definitions of STP, many of which are compiled in this Wikipedia article. Some of them are also used in the aerosol field, so be aware of these possible differences.

All papers reporting ug m-3 of aerosol should state the basis of the m-3 in the experimental section. We recommend the use of the unit ug sm-3 for concentrations reported under STP conditions, and of ug am-3 for concentrations reported under ambient conditions.

Do the detection limits change with the averaging time?

interval changes, see time stamp. Detection limits are given for the actual time period of the measurements.

From previous results, the DLs scale as the inverse sqrt of the averaging time. DL estimates were derived

with the method of Drewnick et al. (Atmos. Meas. Tech., 2, 33-46, 2009).

Is the AMS "organics" the same as "OC" or "organic carbon" measured with other instruments and reported by some models?

"Organics" correspond to organic

aerosol mass (often referred to as OM or OA). It includes OC (organic carbon), as well other atoms (H,O,N) in

organic species.