Aerosol mass spectrometry
Analysis of these particles is important owing to their major impacts on global climate change, visibility, regional air pollution and human health.
These ideas were expanded on between 1880 and 1890 by meteorologist John Aitken who demonstrated the fundamental role of dust particles in the formation of clouds and fogs.
Aitken's method for aerosol analysis consisted of counting and sizing particles mounted on a slide, using a microscope.
The setup is quite similar to today's AMS system, with the sample being introduced through a small steel capillary into the ion source region.
The method could only ionize elements with ionization potentials below the work function of the filament (~8 eV), typically alkali and alkaline earth metal.
In Davis's analysis of ambient air, he found a significant increase in lead at the end of the day, which was concluded to be due to automobile emissions.
[6] The PIMS instrument was the first to have a deferentially-pumped direct inlet that consists of a stainless steel capillary, followed by a skimmer and conical collimator that focuses the sample into a particle beam that goes on to the ionization region.
Prior to this point all RTSPMS methods used surface desorption/ionization (SDI) which consist of a heated metal that ionized the samples.
[6] The LDI method involves the sample being hit with a continuous wave, where the particle absorbs photons, and undergoes both desorption and ionization by the same pulse.
LDI has several advantages over SDI for on-line single particle mass spectrometry, as such since its development it has been the primary ionization method for RTSPMS.
Prather developed the aerosol time-of-flight mass spectrometry (ATOFMS), this method was the first that allow for simultaneous measurement of size and composition of single airborne particle.
[6] Off-line is an older method than on-line and involves the chemical analysis of sampled aerosols collected traditionally on filters or with cascade impactors (shown to the right) in the field and analyzed back in the lab.
Cascade impactors collects particles as they transverse a series of impaction plates, and separate them based on size.
ICP is commonly used in the elemental analysis of trace metals, and can be used to determine the source of the particles and their health effects.
On-line Mass spectrometry solves these problems through the collection and analysis of aerosol particles in real time.
Once in the chamber the sample goes through aerodynamic focusing lens system, which consist of several orifice lenses that are mount in sequence of decreasing inner diameter.
The main advantage of using LDI over thermal desorption, is the ability to analyze both non-refractory and refractory (e.g., mineral dust, soot) components of atmospheric aerosols.
The inlet system is similar to the AMS by using the same aerodynamic focusing lens, but it has smaller orifices because of its analysis of single particles.
In the sizing region particle passes through the first continuous solid state laser that generates an initial pulse of scattered light.
Its growth is partly due to the instruments versatility, it has the ability to analyze a particles size and chemical composition, and perform bulk and single-particle measurements.
Over the years aerosols mass spectrometers have been used for anything from determining emissions sources, human exposure to pollutants, radiative transfer and cloud microphysics.
Most of these studies have utilized the mobility of the AMS and has been fielded in urban, remote, rural, marine, and forested environments around the world.
[3] One recent emission study in 2014 was performed by two NASA research aircraft, a DC-8 and a P-3B, that were outfitted with aerosol instrumentation (AMS).
The aircraft were sent to perform analysis of atmospheric samples over the oil sands mining and upgrading facilities near Ft. McMurray, Alberta, Canada.
