| Popis: |
Aerosol chemical composition as a function of particle size was determined in the southwestern U.S.A. during four weeks of sampling in June, July and December, 1979 as a part of project VISITA. Samples were collected at two ground stations about 80 km apart near Page (AZ) and in two aircraft flying throughout the region. Several different size separating aerosol samplers and chemical analysis procedures were intercompared and were used in determining the size distribution and elemental composition of the aerosol. Sulfur was shown to be in the form of water soluable sulfate, highly correlated with ammonium ion, and with an average [NH + 4 ]/[SO 2− 4 ] molar ratio of 1.65. During the summer sampling period, three distinct regimes were observed, each with a different aerosol composition. The first, 24 h sampling ending 30 June, was characterized by a higher than average value of light scattering due to particles (b sp ) of 24 × 10 −6 m −1 and a fine particulate mass ( M f ) of 8.5 μg m −1 . The fine particle aerosol was dominated by sulfate and carbon. Aircraft measurements showed the aerosol was homogeneous throughout the region at that time. The second regime, 5 July, had the highest average b sp of 51 × 10 −6 m −1 during the sampling period with M f of 3.2 μgm −3 . The fine particle aerosol had nearly equal concentrations of carbon and ammonium sulfate. For all three regimes, enrichment factor analysis indicated fine and coarse particle Cu, Zn, Cl, Br, and Pb and fine particle K were enriched above crustal concentrations relative to Fe, indicating that these elements were present in the aerosol from sources other than wind blown dust. Particle extinction budgets calculated for the three regimes indicated that fine particles contributed most significantly, with carbon and (NH 4 ) 2 SO 4 making the largest contributions. Fine particle crustal elements including Si did not contribute significantly to the extinction budget during this study. The December sampling was characterized by very light fine particle loading with two regimes identified. One regime had higher fine mass and sulfate concentrations while the other had low values for all species measured. |
