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: Rudolf Husar, rhusar@mecf.wustl.edu

What is Particulate Matter?

• The term Particulate Matter or aerosol, refers to liquid or solid particles suspended in the air. Depending on their origin and visual appearance, aerosols have 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, so the 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

How Does PM Vary?Spatially, temporally, with particle size and

by chemical composition

• As all pollutants, the ambient aerosol concentration patterns contain endless variability in space and time. However, unlike gaseous pollutants, particulate matter 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 and secondary 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 particles from different sources internally into particles with mixed composition.

• The result is a heterogeneous PM pattern that is probably unparalleled in the domain of atmospheric sciences. For instance it is common to find soot particles within sulfate droplets, or nitrate deposited on sea salt particles.

The Influence of Emissions, Dilution and Transformations

• The PM concentration, C, at any given location and time is determined by the combined interaction of emissions, E, atmospheric dilution, D, and chemical transformation and removal, T, processes:

C = f (E, D, T)• Each of the three processes

has its own pattern at secular, yearly, weekly, synoptic, diurnal and micro time scales.

• The yearly, weekly and the diurnal scales are periodic

Resource Links

• Workbook Table of Contents• Comment and Feedback Page• Applications / Reports• Data sets used in the Applications• Methods and tools used in the Applications