Particulate Matter concentrations continue to range in the Yellow to Orange AQI levels along the Western half of the United States, as shown in EPA's Airnow animation. According to NOAA's Air Quality Forecast Guidance surface PM2.5 concentrations in California continue being impacted by the smoke from the forest fires reported here last week. In the Rocky Mountains, temperature inversions are trapping pollutants into valleys increasing PM2.5 concentrations. In the Eastern US, mainly Northern Mid-Atlantic US, an Arctic high pressure system moved in, with colder and dry air causing particle concentrations to decrease. PM2.5 concentrations reached Moderate levels due to a morning temperature inversion, influenced by the snow on the ground.