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Airborne Dust - Types & Hazards

We do many projects that relate to the measurement and improvement of indoor air quality. As a result, we receive many questions, some of which we hope to answer here regarding Ultra-Fine Particles (UFPs), types, acceptable amounts, and how you can protect your indoor air quality. If you have a question, please contact us.

Dust, of course, is a part of our daily lives.  But understanding the relative hazards of various TYPES of dust is an important part of managing the risks associated with each.  Read on.

  1. Particulate matter (PM) contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health problems. Some particles less than 10 micrometers in diameter can get deep into your lungs and some may even get into your bloodstream. Of these, particles less than 2.5 micrometers in diameter, also known as fine particles or PM2.5, pose the greatest risk to health. Fine particles are also the main cause of reduced visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas.
  2. PM 10.  Nuisance dust and pollens.  These include dust particles smaller than (<) 10 microns.  Prevalent in construction dust.  Not as hazardous as PM 2.5 (see below), but should be kept below 60 ug/m3 if possible.  Like a nesting doll, PM 10 actually includes PM 2.5 particles. 
  3. PM 2.5.  Also known as “respirable dust” since it can be drawn more deeply into the lungs and is thus more dangerous.  <2.5 microns. 
  4. Ultra-Fine Particles (UFPs)  UFPs are those particles measuring less than 0.1 microns in diameter.  In any given sample of air, UFPs constitute the greatest number of particles, yet make up only a small fraction of the mass.  IAQ investigations in thousands of buildings have already shown UFPs to be directly related to complaints.  UFPs are usually products of combustion or chemical reactions.  Engine exhaust, laser printers, and leaf blowers are possibly the 3 primary generators of UFPs. 

Generally, we’ve found the following average UFP concentrations in sampled environments – expressed in particles per cubic centimeter, or p/cc.  (Results must be considered anecdotal until additional data can be processed.)

  • Open countryside, clear skies, no fires:  500 -600 p/cc
  • Urban office environments with a well-maintained HVAC system: 800 – 2000 p/cc
  • Urban intersections with high vehicular traffic:  15,000 -26,000 p/cc
  • Outside beneath jet aircraft landing paths:  7500 (median) to 55,000 (maximum)  p/cc.
  • 10 to 20 yards from a commercial leaf blower during and shortly after use near a university parking lot::  30,000 to 50,000 p/cc.

Summary:  A well-maintained, roof-mounted heating, ventilation, and air conditioning (HVAC) system, in which filters are periodically and regularly replaced, is generally effective in maintaining indoor UFPs at acceptable levels, even in urban environments.  Based on data gathered so far, we believe the use of motorized leaf blowers should be greatly reduced or eliminated where possible.