|dc.description.abstract||Owing to fast variations of atmospheric aerosol in temporal scale, aerosol time variations and source contributions can only be resolved by way of continuous monitoring. This study adopts continuous monitoring data ranged from March 2003 to December 2008 at the North Aerosol Supersite of the Taiwan Environmental Protection Administration to investigate the effects of environment factors and pollution sources on aerosol properties. The study subjects include aerosol property variations in recent seven years, the influence of continental high, formation of secondary organic carbons, comparisons of mobile vehicle emissions and photochemical reactions, aerosol properties in the selected events (Yellow Dust, Festivals, and high concentration), and atmospheric visibility affected by aerosol extinction.
The results show that the level of most aerosol components except for sulfate has a decreasing trend in years. In addition, most aerosol components apparently have the highest level in winter and with the lowest level in summer in a year. Nonetheless, organic carbon (OC), elemental carbon (EC), and black carbon (BC) exhibit their lowest concentrations in autumn. During years, continental cold-high event, Yellow Dust event, and high concentration event frequently occurred in autumn and winter. For continental cold-high event and Yellow Dust event, high PM2.5 sulfate level was observed when the air masses transport along the coastline of Mainland China. High concentration event is selected by having daily PM2.5 level above 50 μg m-3. This event is caused by weather type such as anticyclonic outflow or high-pressure pushing, the former renders local pollution accumulation and the latter transports trans-boundary pollutants to Taiwan. For days with festival activities (e.g., the Spring Festival, the Tomb-Sweeping Festival, the Mid-Summer Festival, and the Moon Festival), pollution is affected by festival activities if the weather does not interfere with pollutant behaviors.
Hourly PM2.5 secondary organic carbon was estimated by using (OC/EC) averages taken from 6:00 to 9:00 every morning. The estimated PM2.5 secondary organic carbon appeared in every season and accounted for 10 to 15% of OC. PM2.5 components between the time periods for mobile vehicle emissions and photochemical reactions are compared. Mobile vehicle emissions are found related to higher PM2.5 component concentrations when the daily ozone maximum level is below 80 ppb. In contrast, photochemical reactions are responsible for higher PM2.5 component concentrations when the daily ozone maximum level is above 80 ppb.
Regression analysis on aerosol optical property reveals that aerosol light-extinction is mainly affected by components not detected in PM2.5, PM2.5 nitrate, PM2.5 sulfate, PM2.5 EC, and relative humidity. For atmospheric visibility, it is influenced by PM2.5 nitrate, PM2.5 sulfate, and relative humidity.