7/29/2019 Particulate matter properties http://slidepdf.com/reader/full/particulate-matter-properties 1/16 What is Particulate Matter and How does it Vary? •What is Particulate Matter? •How Does PM Vary? •The Influence of Emissions, Dilution and Transformations •Resource Links Contact: rk yadav
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• The term Particulate Matter or aerosol, refers to liquid or solid particlessuspended in the air. Depending on their origin and visual appearance, aerosolshave acquired different names in the everyday language.
• Dust refers to solid airborne material, dispersed into aerosol from grainy powders such as soil.
• Combustion processes produce smoke particles, but the incombustible residues
of coal are called flyash.
• In the early days, air pollution had the appearance of both smoke and fog, sothe term smog was created.
• In the open atmosphere, the visibility may often be reduced by regional haze,originating from various natural or anthropogenic sources.
• Neither water droplets of fog and clouds, snow, rain, sleet (hydrometors) nor dust particles larger than 100 um (blowing sand) are considered to be particulate matter
• Usually, the PM mass is plotted vs. the log of particle diameter
• The mass distribution tends to be bi-modal with the saddle in the 1-3 um size rage• PM10 refers to the fraction of the PM mass less than 10 um in diameter
• PM2.5 or fine mass are less than 2.5 um in size.
• The difference between PM10 and PM2.5 constitutes the coarse fraction
• The fine and coarse particles have different sources, properties and effects. Many of the
known environmental impacts (health, visibility, acid deposition) are attributed to
• As all pollutants, the ambient aerosol concentration patterns contain endlessvariability in space and time. However, unlike gaseous pollutants, particulatematter also depends on particle size, shape and chemical composition.
• The chemically rich aerosol mix arises from the multiplicity of PM sources,
each having a unique chemical signature at the source.• The primary aerosol chemical composition is further enriched by the addition
of secondary species during atmospheric transport.
• The effective mixing in the lower atmosphere stirs these primary andsecondary particles into an externally mixed batch with various degrees of homogeneity, depending on location and time.
• Lastly, repeated cloud scavenging and evaporation tends to mix the particlesfrom different sources internally into particles with mixed composition.
• The result is a heterogeneous PM pattern that is probably unparalleled in thedomain of atmospheric sciences. For instance it is common to find soot particles within sulfate droplets, or nitrate deposited on sea salt particles.