The Major Components of PM2.5 at Remote Sites across the United States

Eldred, Robert

The IMPROVE (Interagency Monitoring of Protected Visual Environments) network measures the concentrations of the major components of PM2.5 mass at 70 sites throughout the United States: sulfate, nitrate, organics, elemental carbon (EC), and soil. The calculation of these components is discussed. The only components that inter-correlate are organics and EC, with EC being 10% to 18% of organics. The spatial patterns of the annual concentrations are discussed. Sulfate is much higher in the East than in the West. Organics and EC shows less variation between regions. In the East , the means increase from north to south. In the West, they are highest in the Northwest and California. Nitrate is generally higher in the East, but is highest at sites near western urban areas. Soil tends to increase from north to south with little east-west difference. The relative contributions of the five components are examined. In the East, sulfate accounts for 60% of the total and organics plus EC 30%. In the Northwest, organics plus EC account for 50% and sulfate 25%. In the Southwest, sulfate, organics, and soil are approximately equal. The seasonal variations are discussed briefly. Comparisons are also made of two urban sites (Washington DC and Seattle) with nearby sites at Class I areas. Of all the components, sulfate shows the least variation from remote to urban.