U.S. Air Quality

First rain, then smoke

After the extensive rainfall experienced in past days, "clear" (to the human eye) skies prevailed as a high surface pressure system settled over the region. Good PM2.5 AQI levels were measured at MDE monitoring stations in Beltsville, Hagerstown and Oldtown. The PM2.5 measurements ranged from 0-3, 4-8, and 4-7 ug/m3, respectively. In today's lidar timeseries, left figure, an homogeneous boundary layer can be observed reaching heights up to 2 km. The layer observed between 3-4 km is probably due to smoke from the Mexican fires that developed a few days back and were showcased by Ana. The image on the left combines airmass backtrajectories from NOAA's HYSPLIT and fires from MODIS Active Fire Program Product from the USDA Forest Service. Here is shown that the airmass (and particles aloft) between 3-4 km observed by ELF had been transported from central Mexico, where the fires are still active.