Have you noticed that every winter a thick haze settles over the Valley? It can be seen most prominently in the mornings when the air is coolest. Even as the day brightens and the air warms, the haze remains present.

Why does this happen?

During the winter months, the Phoenix area experiences what is called a temperature inversion. This occurs when a layer of warm air blankets and traps colder air below. During the summer, warm air rises and mixes in the atmosphere, allowing the pollutants at ground level to disperse. However, during the winter, very little of this thermal mixing occurs. At night when the air cools, the inversion intensifies, especially when the weather conditions are clear and calm. Because of our unique topography and weather patterns, the air at ground level can sometimes remain stagnant for long periods and become infused with pollution like smoke (PM_2.5) and dust (PM₁₀).

When air pollution in Maricopa County is projected to reach unhealthy levels, the Maricopa County Air Quality Department (MCAQD) will issue a No Burn Day. No Burn Days often accompany High Pollution Advisories, which are based upon the meteorological and air pollutant data monitored by the Arizona Department of Environmental Quality (ADEQ). When a No Burn Day is issued, wood burning is prohibited in Maricopa County with few exceptions.

PM_2.5 are fine particulates that measure less than 2.5 microns in diameter, small enough that they are beyond the detection of the naked eye. One concern related to PM_2.5 is how it negatively impacts our health. Because individual particulates are microscopic in size, when we breathe, they travel deep into our lungs and become embedded. For this reason, higher levels of PM_2.5 pollution can lead to breathing complications for those with asthma and compromised immune systems.   

Throughout the year, combustion sources like automobiles and power plants contribute to the levels of PM_2.5 in Maricopa County. During the winter months, however, wood burning in fireplaces, backyard firepits, and chimineas becomes more prominent, contributing a larger share to the overall levels of PM_2.5. This is especially noticeable on nights around the holidays when smoke is heaviest in the Valley.

Maricopa County TRP 2023 Cost Study Now Available!

During the September 2023 TRP Regional Task Force (Task Force) public meeting, the TRP 2023 Cost Study was approved. The cost study provides employer industry averages that consider unique circumstances and costs when reviewing an organization’s proposed travel reduction plan (plan). Regular periodic evaluations of average per employee cost by industry are used to inform TRP staff in addressing budget concerns during the plan review process and provide benchmarks used by the Task Force to assess whether a plan should be approved.

While the overall employers per person average cost decreased across all industries, many participating employer industries single occupancy vehicle trips and miles traveled rates are well below the 60% reduction goal. One likely influence on these findings is the significant increase in teleworking across various industries over the last several years.

If you would like more information on the TRP 2023 Cost Study, contact TRP staff at TRP@maricopa.gov or call the TRP Main Line at 602-506-6750.