Document Type

Article

Journal/Book Title/Conference

International Symposium on Erosion and Landscape Evolution, ASABE

Issue

11020

Publication Date

9-18-2011

Abstract

Wind erosion can affect agricultural productivity, soil stability, and air quality. Air quality concerns deal mainly with human health and welfare issues, but are also related to long range transport and deposition of crustal materials. Regulatory standards for ambient levels of particulate matter (PM) with equivalent aerodynamic diameters ≤ 10 μm (PM10) and ≤ 2.5 μm (PM2.5) have been established in many countries in an effort to protect the health and welfare of their citizens. Wind erosion events may lead to high PM levels that exceed air quality standards and are health hazards. Quantifying suspended wind-blown dust emissions and resulting PM concentrations from wind erosion events are, therefore, of significant interest. A high wind event causing visible soil suspension occurred on May 20, 2008 in California’s San Joaquin Valley. On this day, PM concentrations around a 10 hectare field with fine sandy loam soil were being measured as part of an agricultural tillage PM emissions study. Meteorological parameters were monitored by a weather station at 5 m and two 15.3 m towers vertically profiling wind speed, wind direction, temperature, and humidity. Point sensor PM instruments deployed were a vertical and horizontal array of optical particle counters (OPCs) and portable filter-based PM samplers. A remote sensing scanning Lidar (light detection and ranging) system with three wavelengths (1064 nm, 532 nm, and 355 nm) called Aglite was also deployed. The OPCs were used to calibrate the Lidar return signal to particle count and volume concentration. Mass concentration calibrations for both the OPCs and Lidar were calculated from OPC and filter-based PM data collected that day. The filterbased sampling was stopped upon completion of the tillage activity while the OPCs and Lidar continued to collect data during part of the wind erosion event. Since this was not designed as a wind erosion study, measurements of neither creep nor saltation were made. Emission rates (ERs) were calculated by a technique using a vertical flux equation with OPC-measured PM data, an inverse modeling technique using AERMOD with OPC-measured PM data, and through the application of a mass balancing technique to upwind and downwind vertical Lidar scans. PM values measured downwind of the field were consistently much higher than those measured upwind, showing significant suspension and vertical dispersion of soil particles from the field up to 9 m. Particle size distributions and PM levels were also consistently higher at 2 m than 9 m in both upwind and downwind locations, suggesting most particles in the wind-blown dust plumes stayed near the surface. All OPCs, especially those downwind, had high counts for particles > 1 μm relative to counts of particles < 1 μm in comparison with typical ambient atmosphere particle size distributions. The Lidar detected wind-blown dust plumes of varying size, location, and duration on the downwind field edge from 10 m to 50 m in elevation. ERs based on the vertical flux equation were 3.9 μg/s-m2 for PM2.5, 174.2 μg/s-m2 for PM10, and 872.0 μg/s-m2 for TSP while ERs from inverse modeling were 6.1 μg/s-m2 for PM2.5, 268.7 μg/s-m2 for PM10, and 1,488.9 μg/s-m2 for TSP. These PM10 ERs are similar to other values in literature. The Lidar-based ERs were three orders of magnitude lower than those from the other two methods. A minimum measurement height of ~10 m due to safety concerns prevented the Lidar from adequately detecting plumes that are close to the ground, such as the wind erosion plumes seen on this day.

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