Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2015
Publication Date: 11/1/2015
Citation: Stout, J.E. 2015. Diurnal Patterns of Blowing Dust on the Llano Estacado. Journal of Arid Environments. 122:85-92.
Interpretive Summary: Gravimetric sampling is the standard method for determining dust concentration and forms the basis for regulation of ambient particulate matter concentrations under the U.S. Federal Clean Air Act. The standard protocol for gravimetric sampling requires 24-hour sampling in order to accumulate enough mass on a filter to weigh it accurately. A 24-hour dust sample can provide valuable information about long-term changes of ambient dust levels but it masks important information about short-term variations. Of particular interest is the diurnal pattern of dust concentration. Using hourly dust data collected in Lubbock, Texas, over a period of five years, the diurnal pattern of dust concentration was computed. The results of this analysis suggest that the overall diurnal pattern is characterized by relatively high dust concentrations during the day and relatively low concentrations at night and in the early morning.
Technical Abstract: Using a Tapered Element Oscillating Microbalance (TEOM), hourly dust data was collected in Lubbock, Texas, from January 1, 2003, to January 1, 2008. Diurnal patterns of dust concentration were computed by averaging hourly values associated with a given “time of day” for all days within the 5-yr sampling period. The results of this analysis suggest that the overall diurnal pattern is characterized by relatively high dust concentrations during the day and relatively low dust concentrations at night and early morning. Diurnal patterns of blowing dust are influenced by diurnal variations of key climatic factors. Generally, one finds relatively strong winds during the day and lighter winds at night. The morning increase in wind speed is associated with the rising sun and the resulting rise in incoming solar radiation. Solar radiation produces thermal instability and enhances the mixing of high momentum winds from the upper levels of the atmosphere to the surface layer. Solar radiation can also reduce the critical threshold by drying the soil surface. Diurnal patterns of blowing dust were also computed for each of the four seasons. Seasonal distributions were found to follow a pattern that was similar to that of the overall data set, however, with a few subtle but important differences. The most conspicuous change of the diurnal pattern occurred in the summer where the difference between peak afternoon values and early morning values was considerably less than that of other seasons. The fact that there is not a strong diurnal pattern in the summer suggests that this season lacks major dust storms so that the ambient dust concentration tends to hover near the mean concentration during the summer months.