The annual Emissions Monitoring Program estimates emissions and identifies areas of exposed playa for proactive dust control. It also identifies the location and magnitude of emissions potential in desert areas adjacent to the Sea. The emissions estimate involved establishing the Air Quality Monitoring Network, and these key steps: 1. Map Exposure, 2, Characterize Surfaces, 3. Model Wind Conditions, and 4. Estimate Emissions.

 

Air Quality Monitoring Network

The Salton Sea Air Quality Monitoring Network includes multiple air quality, meteorological, and camera stations for the purpose of monitoring and characterizing windblown dust in the Imperial Valley.

The network includes 6 permanent and 5 portable stations around the Salton Sea, and 3 portable stations in the desert.

The network was developed and is maintained by IID, in collaboration with the California Air Resources Board and the Environmental Protection Agency.

Air Quality Monitoring Stations

The six permanent monitoring stations located around the Salton Sea are near existing communities, known emission sources, or sensitive receptor areas. These permanent stations monitor hourly average mass concentrations of particulate matter and associated meteorological parameters on a continuous basis. At each permanent station, a TEOM instrument continuously measures particulate matter concentrations. At two of the permanent stations, a Partisol instrument collects filter samples to provide elemental information on the chemical composition of the particles.

Meteorological Towers

Meteorological towers are also installed near each permanent station. The meteorological towers at the permanent monitoring stations are about 30 feet tall and measure wind direction, wind speed, relative humidity, solar radiation, and temperature. The portable and field scale pilot study meteorological towers are 6-meter stainless steel tripods with anchored guy wires. The portable monitoring stations monitor wind speed and direction at various locations and heights.

Cameras

Two Roundshot cameras provide a 360-degree panoramic image every 10 minutes during the daylight hours. The Roundshot cameras provide live views of conditions at the south end of the Salton Sea and near Anza-Borrego in the Ocotillo Wells State Vehicular Recreation Area. Additional still-frame cameras are distributed around the Sea. The images can be viewed on the DustCam Viewer.

 

1. Map Exposure

Playa exposure is analyzed at the end of each year, when the Sea is at the lowest point of the hydrological cycle. Analysis includes use of satellite imagery, United States Geological Survey (USGS) water-surface elevation data, and high-resolution bathymetric data. The end-of-year 2002 shoreline (prior to the start of the conserved water transfer) serves as the baseline from which subsequent years are compared. Therefore, exposed playa for 2018 is defined as the total area of exposed land between the former Salton Sea shoreline at the end of 2002 and the shoreline at the end of 2018. Exposed playa is currently about 20,910 acres (32 square miles), including approximately 15,930 acres of bare playa, 4,290 acres of vegetation, and 690 acres of open water. The elevation of the Sea is expected to stabilize around 2047. At that time, the Salton Sea will be approximately two-thirds of its current size and there will be an estimated 130 square miles of exposed playa.

The timing and location of playa exposure is a function of the Salton Sea floor elevation and the Sea’s response to inflows, salt loads, and evaporation rates. Models originally developed to simulate the effects of the water transfer on Salton Sea elevation and salinity have since been refined to help estimate projected playa exposure. Projected playa exposure using the “median” model run is very close to actual playa exposure. Projected versus actual playa exposure will continue to be monitored as part of the Air Quality Mitigation Program.

 

2. Characterize Surfaces

Playa and desert surfaces are characterized annually to provide a better understanding of the type, location, and extent of surfaces vulnerable to erosion. Surface characteristics are directly related to the spatial and temporal nature of PM10 emissions. The primary playa surface types are no-crust, smooth, weak botryoidal, botryoidal, and barnacles (image below). Playa surface characteristics are mapped using remotely-sensed data resources and ground-based surface evaluations. Each surface is sampled with a PI-SWERL, or Portable In-Situ Wind ERosion Laboratory, which simulates various wind speeds to measure the potential for surface and soil erosion (and associated dust emissions) of different surface types. PI-SWERL results are then used to identify the primary drivers of emissions.

Emissions potential is highly variable, but is driven by surface type, surface moisture, and the presence of loose surface sand. Overall, playa surfaces dominated by coarser-textured (sandy) soils have more predictable emissions because emissions are largely a factor of saltating sand. In contrast, emissions from playa surfaces with finer-textured, clay soils have less predictable emissions because of sensitivity to environmental influences. For example, precipitation events, diurnal temperature changes, and relative humidity can cause playa surface characteristics to change and increase (or decrease) the potential for erosion. In the desert, surface types range from relatively stable surfaces, like cobble and bedrock, to more emissive surfaces, like dry washes, sand sheets, and sand dunes. Sand intrusion from these areas will increase the emissions potential of exposed playa due to the associated surface disturbance and erosion.

 

3. Model Wind Conditions

Weather variables, like wind speed and wind direction, play a pivotal role in emissions potential. Although there are numerous point weather observation stations in the study area, the station data only represent the point of collection and adjacent areas, and thus are not suitable to support estimation of dust emissions throughout the entire study area. Accordingly, the Weather Research and Forecasting model is used to estimate wind speed and wind direction based on almost 70 weather stations. Results are used to inform the emissions estimates and to identify and relate high wind speed events to observed emissions from the playa.

 

4. Estimate Emissions

As described previously, the emissions estimates for the playa and the desert are based on the extent of various surface types, the surface characteristics and associated emissions potential, and simulated wind conditions. It is important to remember there are other non-negligible factors that impact PM10 emissions potential. Nevertheless, these emissions estimates are comprehensive and calculated based on the best available datasets and scientific methodology. Results are available in the Annual Reports for the Emissions Monitoring Program (available on the Documents page).

The annual Emissions Monitoring Program is designed to work in tandem with proactive dust control planning and implementation to proactively mitigate windblown dust emissions at the Salton Sea. For example, existing and planned dust control pilot projects, as well as projects planned by other stakeholders, will cover over 7,750 acres. These areas account for over 51% of the total yearly playa emissions. More specifically, assuming 95% design control efficiency per project, the playa emissions estimate is 0.63 tons/day, compared to a playa emissions estimate of 1.23 tons/day with no dust control projects.

Playa

The median emissions estimate for the 2017/2018 monitoring year is 1.23 tons/day. Compared to the emissions estimate for the prior monitoring year, this represents approximately a 20% increase. This increase can be attributed, in part, to an increase in playa acreage and the fact that playa surfaces become more emissive as the duration of exposure increases and playa surface moisture decreases.

Desert

For the desert, the median emissions estimate for the 2017/2018 monitoring year is 124 tons/day.