Emissions Monitoring Program

Map Exposure
Characterize Surfaces
Model Wind Conditions
Estimate Emissions

IID estimates emissions annually from the playa and the desert. Emissions refer to windblown particulate matter less than 10 microns in diameter (PM10). Results inform prioritization and implementation of dust mitigation activities under the SS AQMP. An independent peer review of the emission estimates methodology, consistent with EPA's peer review guidelines, confirmed the approach is scientifically rigorous and appropriate for identifying high priority playa areas for dust mitigation.

The Emissions Monitoring Program includes:


Map Exposure

Characterize Surfaces

Model Wind Conditions

Estimate Emissions
Map Playa 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, water-surface elevation data, and high-resolution bathymetric data.

Playa exposure is a function of how the Salton Sea responds to inflows, salt loads, and evaporation rates. Based on modeling completed in 2018, approximately 20,000 additional acres of playa are anticipated to be exposed every five years. However, actual playa exposure has been less. 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.

End-of-year 2023 totals include:
...

Characterize Surfaces

Playa and desert surfaces are characterized annually to assess the type, location, and extent of surfaces vulnerable to erosion. Surface characteristics are mapped using remotely-sensed data resources and ground-based surface evaluations.

Surface characteristics are directly related to the spatial and temporal nature of PM10 emissions.

Playa Surfaces Are Dynamic and Change Over Time
Model Wind Conditions

Weather variables, like wind speed and wind direction, play a pivotal role in emissions potential. The Weather Research and Forecasting model is used to estimate wind speed and direction based on almost 70 weather stations. Results are used to inform the emissions estimates and to relate high wind speed events to observed emissions.

Example illustrating how wind speed and direction from a high wind event (April 2023) are used to model the location and magnitude of emissions from the desert and from the playa. The controlled playa conditions reflect IID and other stakeholder projects that are planned or implemented in areas that contribute over 65% of emissions from the five-year average annual emissions estimates.

Estimate Emissions

Emissions are estimated based on the best available datasets and scientific methodology. The entire emission estimate approach is transparent, well documented, and was vetted through a rigorous peer review process in 2021, consistent with EPA's peer review guidelines.

Emissions from the Playa vs the Desert

Emissions are estimated for the playa and adjacent desert areas upwind of the playa. Playa is the area of exposed land between the former Salton Sea shoreline at the end of 2002 and the current shoreline. The desert area is bound by the Imperial Valley, the Mexico-United States border, the Peninsular range, and Desert Shores.

Desert emissions dominate the total emissions in the airshed, contributing more than 95 times more PM10 to the airshed than playa sources. Emissions are primarily driven by geomorphic surface type and are highest in sand dominated areas. Other factors that influence emissions potential include the presence and density of vegetation, time since significant rainfall, and time since a flash flood event (which can replenish erodible fine dust on dry wash surfaces).

Playa emissions contribute about one percent of the total PM10 to the airshed. Playa emissions are primarily driven by surface type, soil moisture, and the presence of loose surface sand. Depending on these factors, the emissions potential can range from no emissions to 35 tons per square kilometer.

Emissions are highest in the southern and central portions of the western desert area. These areas are predominantly sand sheets, which are the most abundant of the emissive surface types in the western desert.

Approximately 20% of the playa is responsible for nearly 73% of playa emissions.

The western playa is responsible for the majority of playa emissions due to dry washes and unlimited sand migration from the desert.

Existing and planned dust control projects are located in areas that contribute 71% of the five-year average annual emissions estimate.