| dc.description.abstract | The purpose of this study is to characterize the chemistry and microphysics of the wintertime stratiform clouds in northern Taiwan. The experiment of cloud water collection was established at Mt. Bamboo (25°11’’ N，121° 31’’ E，1103 m MSL) in the winters of 1996 - 2007. Cloud events were categorized to study the relationship between cloud varions types. Backward trajectory analysis was used to categorize the source of cloud-forming air mass that arrived at the site. We also summarized the 12-year cloud measurements, reported the trend and explained the significance.
In total, 101 cloud events were obtained. Principal ions in cloud water were found to be Cl-, Na+ and SO42- , each contributing 27 %, 24 %, and 17 % to total ions, respectively. On average, pH in cloud water was 4.0. Ninety-five percent of cloud water samples had the pH value less than 5.0. Average ratio of nss-SO42- / NO3- in the cloud water was 2.46, indicating the long-range transport of pollutants. Cloud events can be attributed to northeast monsoon flow (Monsoon) and frontal passage (Front), the average total ion concentration of monsoon clouds were more than twice that of frontal clouds. Consequently, their cloud water loadings of nss-SO42- were 6.73 ?g m-3 and 4.07 ?g m-3, respectively.
On average, cloud droplet diameter (Dv), cloud droplet number (N) and liquid water content (LWC) were 12.9 ± 4.0 ?m, 227 ± 276 cm-3 and 0.23 ± 0.31 g m3, respectively. The larger cloud droplet diameter ( > 15 ?m ) is, the higher then liquid water content is. The total ion concentration was an exponential function of droplet diameter and cloud number, with a correlation of r was -0.34 and 0.35, respectively.
Backward trajectory analysis indicated that about 94 % of air mass came from the industrial region in China. Highest total ion concentration and cloud loading of nss-SO42- were associated with the air mass originated from China. For dust events, the average total ion concentration was more than five times that of non-dust events. The contribution of Ca2+ to total ions in cloud water was 3 % and 6 % for non-dust and dust events, respectively.
During the winters of 1996 through 2007, significant trends of increasing nss-SO42- loading and decreasing pH can be found. In the year of 1996, 86 % of pH values in cloud water were less than 5.0, the year of 2007 that 99 % of cloud water samples had the pH less than 5.0,except for possibly due to increasing SO2 emission in China recently. | en_US |