Soil water content and soil disaggregation by disking affects PM10 emissions

Area of Science:

• Agricultural Science
• Environmental Science
• Atmospheric Science

Background:

• Row crop agriculture in California's San Joaquin Valley is a significant source of particulate matter less than 10 micrometers in aerodynamic diameter (PM10).
• Current air quality monitoring relies on fixed PM10 emission values for tillage, which do not account for variations in soil conditions.
• This limitation hinders accurate assessment of agricultural contributions to air pollution and the effectiveness of mitigation strategies.

Purpose of the Study:

• To evaluate how PM10 mass concentrations from agricultural disking are influenced by soil properties and operational factors.
• To investigate the relationships between gravimetric soil water content (GWC), sequential disking events (D1, D2, D3), and soil's weighted mean ped diameter (WMPD) on PM10 emissions.
• To provide data for refining PM10 emission models and improving air quality management in agricultural regions.

Main Methods:

• Conducted a 2-year study in California's San Joaquin Valley.
• Measured PM10 mass concentrations under varying gravimetric soil water content (GWC), from 14% down to 4%.
• Assessed the impact of sequential disking operations (D1, D2, D3) and soil's weighted mean ped diameter (WMPD) on PM10 levels.

Main Results:

• PM10 concentrations increased logarithmically as soil dried, with values 6-8 times higher at lower GWCs (4%) compared to higher GWCs (14%).
• Increased disking frequency elevated PM10, particularly in drier soils; PM10 for D3 was double that of D1 below 7% GWC.
• While lower WMPD correlated with more disking, high GWC effectively reduced PM10 even with significant soil disaggregation.

Conclusions:

• Soil water content is a critical factor in mitigating PM10 emissions during disking operations.
• Sequential disking amplifies PM10, especially under dry conditions, highlighting the need for dynamic emission factors.
• Incorporating soil parameters like GWC and WMPD into PM10 emission estimates is essential for accurate air quality assessments and evaluating conservation tillage benefits.