Particulate matter refers to a mixture of solid particles and liquid droplets found in the air. Some particles are large enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.

Particulate matter is divided into two different groups.

  • PM2.5: Fine particles that are smaller than 2.5 microns in size. Industrial and residential combustion and vehicle exhaust emit fine particles into the air.  These activities include burning oil, coal, wood, or residential waste.  Fine particles also form in the atmosphere when chemical reactions in the air transform gases such as sulfur dioxide, nitrogen oxides, and volatile organic compounds into microscopic solid or liquid particles.  Fine particles can affect the health of everyone but primarily affect children, elderly and individuals with asthma and cardiopulmonary disease.
  • PM10: Coarse particles that are smaller than 10 microns in size.

The department monitors particulate matter levels in the air at locations across the state.
Additional information regarding PM2.5 and PM10 is available on the EPA's Particulate Matter webpage.

Fine Particulate Matter

On Dec. 14, 2012, EPA revised the National Ambient Air Quality Standard (NAAQS) for PM2.5.  The previous standards for PM2.5 were promulgated in 1997 and 2006 and included an annual standard and a 24-hour standard.  The annual standard, which was set in 1997, was 15 micrograms per cubic meter (µg/m3), and the 24-hour standard, which was set in 2006, is 35 µg/m3.  The revised NAAQS finalized in December 2012 retained the 24-hour standard, but lowered the annual standard from 15 µg/m3 to 12 µg/m3.

Annual Standard for PM2.5: 12 micrograms/cubic meter [µg/m3])

Boundary Recommendation

Date Document

December 2013

2012 PM2.5 Boundary Recommendations

August 2014

EPA 120-Day Letter  for the 2012 PM2.5 Boundary Designations

October 2014

Department Response to the U.S. Environmental Protection Agency


Date EPA Approval Document

MACC Adoption:
September 2015


Missouri State Implementation Plan Revision - Infrastructure Elements for the 2012 Annual PM2.5 Standard

24-Hour Standard: 35 µg/m3

Boundary Recommendation

Date Document

December 2007

2006 PM2.5 Boundary Recommendation

Technical Support Documents for Designation of Areas in Missouri for the PM2.5
24-Hour NAAQS. This document has been split into three parts to speed downloading time.

August 2008

U.S. Environmental Protection Agency Response to Recommendation



EPA Approval


MACC Adoption:
August 2009

Federally Approved Plan:
78 FR 37461

2006 standard for PM10

24-hr PM10 Standard: 150 µg/m3

The 24-hour PM10 standard was unchanged in 2006. This standard is violated if the three-year average of the highest 24-hour concentration each year exceeds 150 micrograms/cubic meter. The 2006 revision also revoked the annual PM10 standard.

Date EPA Approval Document
MACC Adoption:
May 29, 2014
Pending Americold Logistics 24-Hr Particulate Matter NAAQS Consent Judgment

Related Links

Summary of Monitored PM2.5 Values
Summary of Monitored PM10 Values

If you are looking for a document that is not available on our website, please click here to file a Sunshine Law request.