(click on graphs below to view the pdf version of the graph)
In Pima County, the natural desert background comprises about one third of the typical PM10 concentration. Particulate concentrations tend to be higher in winter and increase during dry periods.
Tucson violated the 24-hour PM10 standard after four exceedances were recorded in 1999. The exceedances were found to be due to high wind natural events, along with an extended period of low rainfall. These events were flagged as natural exceptional events. The Pima Cuonty Department of Environmental Quality (PDEQ) has measures in place to protect public health and welfare from airborne dust.
The graph below shows the monthly average trend of PM10 and PM2.5 concentrations at the Orange Grove monitoring site for 2011.
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, after the PM10 standard took effect.
PM2.5 levels over the 12-year 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.