| dc.description.abstract | Abstract
This thesis utilized both ground-level observation and model simulation to investigate comprehensively the causes of high aerosol-concentration events (aerosol events) occurred in the Greater Taipei area. Based on aerosol events compiled in the Greater Taipei area from 2002 to 2005, the associated synoptic weather patterns can be classified into 7 types. Among the identified weather patterns, High-Pressure Reflux, Prior Cold Front, TYPhoon, Pacific High Pressure system stretching westerly, and Weak Southern Wind are related to terrain blocking. The remaining patterns are Weak High Pressure system and Migratory High-Pressure system Pushing, respectively, with the latter one being related to long-range transport.
To study the variation of aerosol properties under the mixed influence of terrain and weather pattern, a field observation was conducted at the urban, suburban, and background sites simultaneously from 14th to 23rd in April 2004. During this field observation, aerosol events occurred under High-Pressure Reflux, Prior Cold Front, and Weak High Pressure system weather patterns. PM2.5 (aerosol aerodynamic diameter less than or equal to 2.5 ?m) sulfate level was quite stable with a fraction of 30% in PM2.5 both at the urban and background sites. It exemplified that PM2.5 sulfate was originated from broad sources. In contrast, PM2.5 nitrate was contributed from local sources. Apparently aerosol accumulates in the stagnant environment when the Taipei basin is on the lee side of Snow Mountains Chain (SMC) under the prevailing wind in High-Pressure Reflux pattern or upwind of Snow Mountains Chain under Prior Cold Front pattern. Both weather patterns aggravated aerosol accumulation in the Taipei basin due to the formation of weak wind area from terrain blocking. In this thesis, the fifth-generation Mesoscale Model (MM5) and Community Multiscale Air Quality Modeling System (CMAQ) were also adopted to investigate the formation mechanism of an aerosol event in the Greater Taipei area. From the modeling, the mix of synoptic weather patterns and terrain blocking is verified to be the cause of an aerosol event in the Greater Taipei area.
For the study of long-range transport pollution from Asian continent, this thesis investigates the transport of yellow dust and PM2.5 components, respectively. In the study of yellow dust event, the weather pattern was found all under Migratory High-Pressure system Pushing pattern. Based on the analysis of monitoring data from North Aerosol Supersite at the Taiwan Environmental Protection Administration, the averages of the hourly PM10 (aerosol aerodynamic diameter less than or equal to 10 ?m) and PM2.5-10 (PM10 - PM2.5) were much higher in the during period as compared to those in the before period. It is interesting to note that the time lapse in the during period was well correlated with the maximum level of both PM10 and PM2.5-10. The aerosol size distribution verified that supermicron particles dominated in the during period, and that submicron particles were predominant in the before and after periods. For the chemical properties of the aerosols, time series results indicated that aerosol sulfate was mostly contributed by the dust transport, and the other components were more related to vehicle exhausts.
In the study of aerosol transport, the model simulation was applied to the movement of a southward high-pressure system to Taiwan. As the simulation revealed, during the transport process, that the fraction of PM2.5 organic carbon in PM2.5 plume only slightly decreased from 22－24% in Shanghai to 21% near Taiwan. However, the fraction of semi-volatile PM2.5 nitrate in PM2.5 decreased from 16－25% to 1%. In contrast, the fraction of PM2.5 sulfate in PM2.5 increased from 16－19% to 35%. It is interesting to note that the fraction of PM2.5 ammonium and PM2.5 elemental carbon in PM2.5 remained nearly constant.
In summary, this thesis began with classifying 7 weather patterns from the study of aerosol events under the influences of synoptic weather patterns and terrain blocking in the Greater Taipei area. Field observation and model simulation of aerosols were subsequently applied to investigate thoroughly the aerosol sources and chemical properties for the most frequently occurred High-Pressure Reflux, Prior Cold Front, and Migratory High-Pressure system Pushing patterns. | en_US |