Meteorological mechanisms in association with long-range transport of Asian dust in April 2001 have been investigated using weather maps, satellite images, TOMS and surface $PM_{10}$ data, backward trajectories, plus modeling output results (geopotential heights, horizontal wind vectors, potential temperatures, and streamlines). The results indicated that long -range transport of Asian dust to the west coast of North America was associated with strong westerlies between the Aleutian low and the Pacific high acting as a conveyor belt. Accelerating westerly flows due to cyclogenesis at the source regions over East Asia transported pollution from the continent to the central Pacific. When the system reached the Aleutian Islands, the intensity of troughs and the westerlies were amplified in the North Pacific. Thereafter the winds between the Aleutian Islands and the Pacific Ocean were more intensified from the air flow transport of the conveyor belt. Consequently, the strong wind in the conveyor belt enhanced the dust transport from the Pacific Ocean to the west coast of North America. This was evidenced by $PM_{10}$ concentration (maximum of about $100{\mu}g\;m^{-3}$) observed In California. Further evidence of the dust transport was found through the observation of satellite images, the distribution of TOMS aerosol index, and the analyses of streamlines and backward trajectories.

To study the characteristics of ammonia and the related compounds, atmospheric aerosols and gases were collected using a triple filter pack sampler, a low volume air sampler, and a three-stage Anderson air sampler in Seoul and Kangwha Island, Korea from Dec. 1996 to Oct. 1997. Ammonia concentrations showed approximately two times higher in summer than in winter at both sites. The highest $HNO_3$ levels were generally observed in summertime at two sampling sites. The average mass concentration of $PM_{2.5}$ in heavily industrialized Seoul was about three times higher than that of Kangwha. In winter, the sum of $NH_4^+$ and its counter ions (such as $Cl^-,\;NO_3^-$, and $SO_4^{2-}$) comprised $30-41\%$ of $PM_{2.5}$ mass concentration at each sampling site. Temperature dependence of particulate nitrate was examined at the urban sampling site. The formation of the nitrate in the fine mode was dependent not only on the amount of precursors but also on the variation of temperature. $(NH_4)_2SO_4$ and $NH_4HSO_4$ coexisted with $NH_4NO_3$ and $NH_4Cl$ at each site. According to the summertime backward trajectory analysis, $NO_3^-$ showed higher level with air parcels transported from northeast Asian continent. On the other hand, the concentration of $SO_4^{2-}$ showed significantly higher level when air masses originated from Pacific Ocean, southern part of Japan, and Korea.

In environmental studies, decisions are often made on the analytical data indicating certain contaminants as being 'detected' or 'non-detectible.' Since detection limits are analytical method specific, one has to first review the concepts and definitions associated with analytical method systems and specifications. In this study, the experimental analytical values for a series of low level standards (for an ionic species) were used as an example to estimate two different method detection limits (MDL). The scores of EPA's MDL and Pallesen's MDL determined by real analytical scores are 0.0575 and 0.0561 mg/L, respectively for our nitrate data. These scores determined by two different MDL models are roughly similar, while there are apparent differences between two methods with respect to statistical and systematical procedure. However, determination of MDL for one's laboratory provides some practical applications which helps to assure one's regulating authorities that one's measured scores are accurate.

Aerosol wall loss is an important factor affecting smog chamber experiments, especially with chambers made of Teflon film. In this work, the aerosol wall loss was investigated in 2.5 and $5.8-m^3$ cubic-shaped Teflon film chambers filled with ambient air. The natural change in the particle size distribution was measured using a scanning mobility particle sizer in a dark environment. The rate of aerosol wall loss was obtained from the deposition theory suggested by Crump and Seinfeld (1981). The measured rates of aero-sol wall loss were In a good agreement with the theoretical and experimental values given by McMurry and Rader (1985), implying that the electrostatic effect enhances particle deposition on the chamber wall. The significance of aerosol wall loss correction was demonstrated with the photochemical reaction experiments using the ambient air.