Particle size distribution and PM concentrations during synoptic and convective dust events in West Texas

Abstract. Dust events are an important and complex constituent of the atmospheric system that can impact Earth’s climate, the environment, and human health. The frequency of dust events in West Texas has increased over the past two decades, yet their impact on air quality in this region is still unclear as there is only one air quality monitoring station that measures only PM_2.5 concentrations (Particulate matter with aerodynamic diameter < 2.5 μm), and there is no information on other PM sizes or particle size distribution. The Aerosol Research Observation Station (AEROS) unit provides insight into the local variation of particle concentration during different dust events and allows for a better understanding of the impact of dust events on air quality. Since the west Texas area is prone to dust events, we were wondering if dust events generated by different meteorological causes (synoptic vs convective) will present similar particle concentrations or particle size distributions. In this project, three different dust events were measured by AEROS and compared. Each dust event originated from a different direction and lasted a different duration. One of the dust events was synoptic (April 10, 2019) and two were convective (June 5 and 21, 2019). Measurements of particle mass and number concentration, size distribution, and meteorological conditions for each dust event were compared. The Synoptic dust event (of April 10) was longer (12 h) and had stronger wind speed conditions (up to 22.1 m sec^-1), while the two convective dust events lasted only 20 and 30 minutes and had lower wind speeds (up to 16.5 and 13.4 m sec^-1 for June 5 and 21, respectively). Observation of PM based on daily and hourly values showed an impact on air quality, yet measurements based on daily and hourly values underestimate the impact of the convective dust events. Observations based on a shorter time scale (10-minutes) reveal the true impact of the two convective dust events. A comparison of particle size distribution showed that all three dust events had an increase of particles in the size range of 0.3 to 10 µm. Some particle sizes even increase the concentration by ~2 orders of magnitude compared to the time before the dust event. Leading us to speculate that the impact on air quality of convective dust events in this region is underestimated with the current (hourly basis) method.