Lidar-assisted measurement of PM10 emissions from agricultural tilling in Californiaʹs San Joaquin Valley – Part II: emission factors

Emission factors for agricultural operations are needed in order to develop reliable PM10 emissions inventories and air quality models for air basins with significant agricultural land use. A framework was developed to analyze the PM10 vertical profiles collected downwind of tilling operations in the San Joaquin Valley. The methods calculate emission factors on the basis of profile shape and assign quality ratings to each land preparation test. Uncertainties in the calculated emission factors and plume heights were used as one criterion for evaluating the relative quality of the reported emission factor. Other quality ratings were based on the magnitude of the difference in measured up- and downwind concentrations, wind direction, whether the tests were conducted near the edges of the field, and how well the proposed model fit the profile data. The emission factors from different operations were compared taking the quality of the emission factor into account. Plume heights and emission factors for 24 valid test profiles ranged from 2 to 20 m (mean=9.8; SD=3.6; MEDIAN=9.8) and zero to 800 mg m−2 (mean=152; SD=240; MEDIAN=43), respectively. Key environmental properties governing PM10 emission from these operations include relative humidity, soil moisture and vertical temperature gradient. Surprisingly, no discernable relationships were found between implement type or wind speed and the measured emission factors.