Measurements Of Oc And Ec In Coarse Particulate Matter In The Southeastern United States

摘要

The organic carbon (OC) and elemental carbon (EC) content of filter-based, 24-hr integrated particulate matter with aerodynamic diameters between 2.5 and 10 μm (PM_(10-2.5)) was measured at two urban and two rural locations in the southeastern United States. On average, total carbon (OC + EC) comprised approximately 30% of PM_(10-2.5) mass at these four sites. Carbonate carbon was measured on a subset of samples from three sites and wasrnfound to be undetectable at a rural site in central Alabama, less than 2% of PM_(10-2.5) at an urban site in Georgia, and less than 10% of PM_(10-2.5) at an urban-industrial site in Alabama. Manual scanning electron microscopy (SEM) and computer-controlled SEM (CCSEM) along with energy dispersive X-ray spectroscopy (EDS) were used to identify individual carbonaceous particles in a selected subset of samples collected at one rural site and one urban-industrial site in Alabama. CCSEM results showed that biological material (e.g., fungal spores, pollen, and vegetative detritus) accounted for 60-70% of the carbonaceous mass in PM_(10-2.5) samples with concentrations in the range of 2-16 μg/m~3. Samples with higher PM_(10-2.5) concentrations (25-42 (μg/m~3) at the urban-industrial site were found by manual SEM to have significant amounts of unidentified carbonaceous material, likely originating from local industrial activities. Both filter-based OC and EC concentrations and SEM-identified biological material tended to have higher concentrations during warmer months. Upper limits for organic mass (OM) to OC ratios (OM/OC) are estimated for PM_(10-2.5) samples at 2.1 for urban sites and 2.6-2.7 for rural sites.