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Particulate Matter

Particulate matter is small solid particles or liquid droplets from smoke, dust, fly ash and condensing vapors. It can be suspended in the air for long periods of time. It is generated from paved and unpaved roads, woodsmoke, burning fuels, earth moving, mining, construction, vacant lots and agricultural activities.

These microscopic particles can affect breathing and respiration, cause lung damage and possibly cause premature death. Children, the elderly and people suffering from heart or lung disease are especially at risk.

The larger particles are mostly deposited in the nasal passages, while the very small particles can penetrate and be deposited in the lung sacs and membranes. Additionally, these particulates can damage paint, increase metal corrosion,soil buildings and clothing and reduce visibility. 

There are two types of particulate matter that are regulated by the EPA: Coarse Particulate Matter (PM10) and Fine Particulate Matter (PM2.5). The number indicates the size of the particle in micrometers. Recent research shows that the smaller particles pose a greater threat than the larger particles. 

Current Particulate Matter Standards:

  • 24-hour average: 150 µg/m3
  • 24-hour average:  35 µg/m3
  • Annual average:   12 µg/m3

Particulate Matter Trends

In Pima County, the natural desert background comprises about one third of the typical particulate matter concentrations. Particulate concentrations tend to be higher in winter and increase during dry periods.

The graph below shows the monthly average trend of PM10 and PM2.5 concentrations at the Orange Grove monitoring site for 2014.

Long Term Trends:

PM10 levels have shown large annual fluctuations due to changing meteorological conditions and localized emissions around the monitoring sites. PM10 monitoring began in Pima County in 1988. The Pima County Department of Environmental Quality (PDEQ) has measures in place to protect public health and welfare from airborne dust.

PM2.5 levels over the monitoring period have been well below the federal health standards.

Effective programs in the Tucson area that help reduce particulate matter levels by promoting the use of alternate modes are:

Alternate modes such as carpooling, taking the bus, walking, and bicycling, and the use of telecommuting all serve to reduce the number of motor vehicles on the road.

For dust control, Title 17 of the Pima County Code outlines activity permits and performance standards required for construction activities.



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