Relationships between direction of wind flow and fine particle sulfur concentrations within and upwind of St Louis, MO

Abstract

The relationships are considered between monthly and quarterly means of the fine particle sulfur (S) concentrations and wind flow direction, period of day and season of the year. The measurements used are those obtained at selected urban and at rural monitoring stations in the St Louis area during the Regional Air Pollution Study in 1975, 1976 and 1977. Higher mean fine particle S concentrations are observed with wind flows from the E compared to the W and from the NE and SE quadrants compared to the NW quadrant. Substantially higher fine particle S concentrations are obtained with wind flows from the E compared to the W even when conditions are selected so that the values of temperature, solar radiation intensity and wind speed are within the same restricted ranges. A consistent increase in the fine particle S concentrations occurs through the late morning and afternoon with decrease in the evening and especially in the early morning during spring and summer months with wind flows from the E. The contributions are estimated for local scale and regional scale processes to the observed fine particle S concentrations. Local scale processes include those involving atmospheric formation and primary emissions each contribute 0.6−1.0 and 0.6 μg m −3 of the fine particle S. Regional scale processes account for the greater part of the observed concentrations especially when the wind flows are from the SE or SW. Regional scale episodes involving passage of warm high pressure systems to the E of St Louis with accumulation of precursors made especially significant contributions to formation of fine particle S. The atmospheric gas phase and liquid phase chemical reactions contributing to the formation of fine particle S are discussed. Emphasis is placed on the effects of chemistry on the seasonal variations in concentrations of fine particle S.