The United States Environmental Protection Agency groups particle pollution into three categories: PM0.1, better known as “ultrafine particulate matter” that are particles smaller than 0.1 µm in diameter; PM2.5 are fine inhalable particles, with diameters 2.5 micrometers and smaller; PM10 is inhalable particles, with diameter that are generally 10 micrometers and smaller.
The California Air Resources Board (CARB) monitors air quality in California. The board measures PM2.5 concentrations from air monitoring stations. California Ambient Air Monitoring Network consist of more than two hundred and fifty (250) monitoring stations operated by federal, state, and local agencies.
Ambient air monitoring utilizes a variety of continually evolving technologies to measure ambient air pollutant concentrations. In California, gravimetric analysis is used to measure particulate matter concentrations for air monitoring. Other source attributions include: conductivity, ionization, mass spectrometry, and particle counting.
Gravimetric analysis is a measurement technology that involves monitoring the change in weight resulting from the accumulation of matter on a substrate such as a filter. In air monitoring, it is used to measure particulate matter concentrations. According to the California Air Resources Board (CARB), PM mass concentrations are calculated by measuring a filter's weight before and after sample collection and then dividing the difference by the total volume of air sampled through the filter.
Mass spectrometry’s air monitoring approach entails: Air Toxics, FRM/FEM, Mobile Monitoring, and Remote Sensing. Mass spectrometry (MS) is a powerful analytical technique. CARB refers and list this technique as one capable of “measuring chemical compounds in simple and complex mixtures.” For example, according to developers at CARB, mass spectrometry ionizes samples and sorts the ions based on their mass-to-charge ratios.
Particle counting measures the amount of light scattered by particles to estimate the number and size of particles present in air. Developers say that particle counting typically involves the use of a laser and detectors to capture light scattered at a particular angle from the beam. According to Cam from CARB, the wavelength of laser light sources results in complex light scattering patterns (Mie scattering) dependent not only on particle size (e.g., PM2.5 and PM10), but shape and refractive index.
Conductivity measurement technologies operate by quantifying the changing flow (e.g., resistance or impedance) of electricity between two electrodes. CARB says this change in electrical characteristics correlates to the concentration of a compound.
Ionization methods can be operated as stand-alone instrumentation or coupled with separation methods. This technology method has gas phase ionization methods for air monitoring generally measure carbon based volatile organic compounds (VOCs).
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