Contrast and correlations between coarse and fine particulate matter in the United States

• PM10–2.5 is more variable than PM2.5, acting as the major driver for PM10 extremes.
• Either PM10–2.5 or PM2.5 can be the major driver for mean PM10 depending on site.
• Harvest and planting affect PM10–2.5, but do not have a strong influence on PM2.5.
• Year-specific data of agricultural activities are essential for emission estimates.
• PM10–2.5 and PM2.5 from traffic sources seem to be emitted by different processes.

The characteristics of concentrations of PM10–2.5, PM2.5, and PM10 at 77 sites in the United States are evaluated. PM10 concentrations show strong spatial variability, with highest levels occurring in the southwestern United States, driven primarily by PM10–2.5. PM10–2.5 and PM2.5 concentrations show different spatial patterns. The highest concentrations of PM10–2.5 were observed at sites in the southwestern US, leading to the highest PM10 concentrations there. The PM2.5 concentrations are the major contributors to the average PM10 concentrations at many sites in the eastern United States. Poor correlations were generally found between PM10–2.5 and PM2.5, suggesting that PM10–2.5 and PM2.5 are generally influenced by different sources. PM10–2.5 is generally more variable than PM2.5 because PM10–2.5 has a higher deposition velocity and is primarily emitted from mechanical processes (e.g. agricultural harvest and construction) that are more influenced by factors including human operation and wind speed leading to a strong episodic nature. As a result of its high variability, PM10–2.5 acts as the major driver for PM10 extremes. PM10–2.5 is significantly correlated with PM10 at all investigated sites, with the average correlation value R2 = 0.79. Correlations of PM2.5 with PM10 (average of 0.37) are overall considerably lower than those between PM10–2.5 and PM10. Different seasonal, weekly, and diurnal patterns were observed between PM10–2.5 and PM2.5 at agricultural, on-road traffic, quarrying, airport, and marine sites. At investigated agricultural sites, while the concentrations of PM2.5 are higher in winter when there are few agricultural activities, PM10–2.5 concentrations are lower in winter months than in summer and autumn months, with highest levels corresponding to harvest and planting. The harvest and planting signatures were not observed in PM2.5 concentrations at any of these sites, suggesting that agricultural activities do not have a strong influence on PM2.5 concentrations.