Sign In
Maryland State Government Maryland Department of the Environment

Particulate Matter

Particulate Matter is made of small particles of solid and liquid material.


The term “particulate matter” (PM) includes both solid particles and liquid droplets found in air. Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes. Particles less than 10 micrometers in diameter tend to pose the greatest health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter are referred to as “fine” particles. Sources of fine particles include all types of combustion (motor vehicles, power plants, wood burning, etc.) and some industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as “coarse.” Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads.


Dust, ash, mist, smoke and fumes


Fuel burning, industrial operations, incinerators, agricultural tilling and motor vehicles


Both fine and coarse particles can accumulate in the respiratory system and are associated with numerous health effects. Coarse particles can aggravate respiratory conditions such as asthma. Exposure to fine particles is associated with several serious health effects, including premature death. Adverse health effects have been associated with exposures to PM over both short periods (such as a day) and longer periods (a year or more).

When exposed to PM, people with existing heart or lung diseases—such as asthma, chronic obstructive pulmonary disease, congestive heart disease, or ischemic heart disease—are at increased risk of premature death or admission to hospitals or emergency rooms.
The elderly also are sensitive to PM exposure. They are at increased risk of admission to hospitals or emergency rooms and premature death from heart or lung diseases.
When exposed to PM, children and people with existing lung disease may not be able to breathe as deeply or vigorously as they normally would, and they may experience symptoms such as coughing and shortness of breath.
PM can increase susceptibility to respiratory infections and can aggravate existing respiratory diseases, such as asthma and chronic bronchitis, causing more use of medication and more doctor visits.


On Plants : Particulate matter can form a film on plant leaves reducing sunlight and subsequently interfering with photosynthesis and plant growth.
On Property

Other effects of particles include soiling and degradation of property, which can be costly in terms of cleaning and maintaining surfaces.
On Visibility

Reduction of visibility occurs when small particles absorb or scatter visible light. Visibility is a national and statewide concern, particularly in recreational settings such as national parks, historical sites and other scenic attractions.

Ozone| Particulate Matter| Sulfur Dioxide
Carbon Monoxide| Nitrogen Dioxide| Lead