The precision and accuracy of the determination of particulate sulfate and fluoride, and gas phase S0 and HF are estimated from the results obtained from collocated replicate samples and from collocated comparison samples for highland low-volume filter pack and annular diffusion denuder samplers. The results of replicate analysis of collocated samples and replicate analyses of a given sample for the determination of spherical aluminosilicate fly ash particles have also been compared. Each of these species is being used in the chemical mass balance source apportionment of sulfur oxides in the Grand Canyon region as part of Project MOHAVE, and the precision and accuracy analyses given in this paper provide input to that analysis. The precision of the various measurements reported here is ±1.8 nmol/m and ±2.5 nmol/m for the determination of S0 and sulfate, respectively, with an annular denuder. The precision is ±0.5 nmol/m and ±2.0 nmol/m for the determination of the same species with a high-volume or low-volume filter pack. The precision for the determination of the sum of HF(g) and fine particulate fluoride is +0.3 nmol/m. The precision for the determination of aluminosilicate fly ash particles is ±100 particles/m. At high concentrations of the various species, reproducibility of the various measurements is ±10% to ±14% of the measured concentration. The concentrations of sulfate determined using filter pack samplers are frequently higher than those determined using diffusion denuder sampling systems. The magnitude of the difference (e.g., 2-10 nmol sulfate/m) is small, but important relative to the precision of the data and the concentrations of particulate sulfate present (typically 5-20 nmol sulfate/m). The concentrations of S0(g) determined using a high-volume cascade impactor filter pack sampler are correspondingly lower than those obtained with diffusion denuder samplers. The concentrations of SO (SO(g) plus particulate sulfate) determined using the two samplers during Project MOHAVE at the Spirit Mountain, NV, and Hopi Point, AZ, sampling sites were in agreement. However, for samples collected at Painted Desert, AZ, and Meadview, AZ, the concentrations of SO and S0(g) determined with a high-volume cascade impactor filter pack sampler were frequently lower than those determined using a diffusion denuder sampling system. These two sites had very low ambient relative humidity, an average of 25%. Possible causes of observed differences in the S0(g) and sulfate results obtained from different types of samplers are given.

Total fluoride (gas plus fine particle), spherical aluminosilicate particles, particulate selenium, arsenic, lead, bro-

Air pollutants were collected in Logan, Cache County, UT, in February 1993 during two periods of atmospheric inversion accompanied by fog. The following atmospheric species were determined: (1) gaseous SO 2 , NO 2 (semi-quantitatively), HNO 3 , NH 3 , and HF; (2) fine particulate SO 4 = , NO 3 -, NH 4 + , F -, H + , C, Si, S, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Pb, Se, Br, and Sr, and; (3) fine particulate mass, which was calculated. The major components of fine particulate matter were carbonaceous material, ammonium nitrate, and ammonium sulfate, while the soil component was small. Calculated, fine particulate mass averaged 80 μg/m 3 and reached concentrations as high as 120 μg/m 3 . SO 2 /SO x and NO 2 /NO y mole ratios generally varied between 0.2 and 0.1 during inversions. These ratios also showed moderate but consistent diurnal patterns. The emission inventory for Cache County indicates sources of SO 2 and NO x but not significant amounts of primary sulfate and nitrate. The observations reported here indicate there is significant conversion of SO 2 and NO x in the presence of excess oxidants to sulfuric and nitric acid that are neutralized by excess ammonia.

The precision and accuracy of the determination of particu-late sulfate and fluoride, and gas phase SO and HF are estimated from the results obtained from collocated replicate samples and from collocated comparison samples for high-and low-volume filter pack and annular diffusion denuder samplers. The results of replicate analysis of collocated samples and replicate analyses of a given sample for the determination of spherical aluminosilicate fly ash particles have also been compared. Each of these species is being used in the chemical mass balance source apportionment of sulfur oxides in the Grand Canyon region as part of Project MOHAVE, and the precision and accuracy analyses given in this paper provide input to that analysis. The precision of the various measurements reported here is ±1.8 nmol/m and ±2.5 nmol/m for the determination of SO and sulfate, respectively, with an annular denuder. The precision is ±0.5 nmol/m and ±2.0 nmol/m for the determination of the same species with a high-volume or low-volume filter pack. The precision for the determination of the sum of HF(g) and fine particulate fluoride is ±0.3 nmol/m. The precision for the determination of aluminosilicate fly ash particles is ±100 particles/m. At high concentrations of the various species, reproducibility of the various measurements is ±10% to ±14% of the measured concentration. The concentrations of sulfate determined using filter pack samplers are frequently higher than those determined using diffusion denuder sampling systems. The magnitude of the difference (e.g., 2-10 nmol sulfate/m) is small, but important relative to the precision of the data and the concentrations of particulate sul-fate present (typically 5-20 nmol sulfate/m). The concentrations of SO(g) determined using a high-volume cascade impactor filter pack sampler are correspondingly lower than those obtained with diffusion denuder samplers. The concentrations of SO (SO(g) plus particulate sulfate) determined using the two samplers during Project MOHAVE at the Spirit Mountain, NV, and Hopi Point, AZ, sampling sites were in agreement. However, for samples collected at Painted Desert, AZ, and Meadview, AZ, the concentrations of SO and SO(g) determined with a high-volume cascade impactor filter pack sampler were frequently lower than those determined using a diffusion denuder sampling system. These two sites had very low ambient relative humidity, an average of 25%. Possible causes of observed differences in the SO(g) and sulfate results obtained from different types of samplers are given.