All Houston monitors meet current health-based standards.

What is it?

“Particulate matter,” also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

What are the health effects?

The size of the particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 microns in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:

  • “Inhalable coarse particles,” also called PM10, are larger than 2.5 microns and smaller than 10 microns in diameter.  For comparison purposes, a human hair is usually about 70 microns in diameter.
  • “Fine particles,” called PM2.5, are 2.5 microns in diameter and smaller. pm-10-24hr-graph

In addition to concerns about health affects, fine particles are the main cause of reduced visibility (haze) in parts of the United States, including many of our national parks and wilderness areas.

What are the sources?

The main sources of PM10 are certain industrial processes, dusty roadways, and windblown dust.  PM2.5 can be directly emitted into the air, or can be formed by a complex chemical reaction of emissions from sources like cars and trucks, industries, and wildfires.

How does Houston stand?

Houston currently meets all health-based standards for particle pollution.  In 2012, EPA adopted new, more stringent annual standards for fine particles.  EPA has not yet determined whether Houston will meet those new standards when they take effect.  However, even if Houston does not meet them immediately, EPA predicts that Houston and most other areas around the nation will meet them quickly due to emission reduction programs already in place.