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Modern particulate samplers use a volumetric flow control system that pulls air through the particle separator at the velocity required to achieve the desired cutpoint. For air pollution applications, the definition of "particulate" does not include uncombined water , and water from a particulate sample must be removed before it is weighed.
The fall speed for small particles can be calculated by mass and geometry, but the complex shapes of pollen and spores often fall slower than their estimated speed modeled with simple shapes. [9] Spores can also be removed from the air from impact; the inertia of the particles will cause them to hit surfaces along their path, instead of flowing ...
Similarly, seeing non-luminous objects requires light hitting the object to cause it to reflect that light. While the effects of observation are often negligible, the object still experiences a change (leading to the Schrödinger's cat thought experiment). This effect can be found in many domains of physics, but can usually be reduced to ...
An impactor is a device that classifies particles present in a sample of air or gas into known size ranges. It does this by drawing the air sample through a cascade of progressively finer nozzles. The air jets from these nozzles impact on plane sampling surfaces and each stage collects finer particles than its predecessor.
Physical methods measure an air sample without changing it, for example, by seeing how much of a certain wavelength of light it absorbs. Chemical methods change the sample in some way, through a chemical reaction, and measure that. Most automated air-quality sensors are examples of active measurement. [5]
For example, Pardon et al. [16] show sampling of aerosols down to a microfluidic air-liquid interface, and Ladhani et al., [17] show sampling of airborne Influenza down to a small liquid droplet. The use of low-volume liquids is ideal for minimising sample dilution, and has the potential to be couple to lab-on-chip technologies for rapid point ...
An illustrative example is the effect of catalysts to speed the decomposition of hydrogen peroxide into water and oxygen: . 2 H 2 O 2 → 2 H 2 O + O 2. This reaction proceeds because the reaction products are more stable than the starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available.
The concentration needed to cause this effect is seen to change as the amount of non-volatile matrix changes. So concentration of solid analyte needs to be considered in the preparation of the solution for analysis so that signal from "hidden" analyte is not missed. [17] To choose the matrix for each solid analyte, three criteria must be ...