| dc.description.abstract | 本文首度利用1994年至2003年環保署設置於台北市五個自動空氣品質監測站的監測數據，研究目標是評估這10年來空氣污染管制在台北市的成效，探討二次污染物及大陸沙塵的影響。本文首先藉由車輛污染源排放減量，檢討對臭氧生成的影響，然後以低光化強度日子的PM10及PM2.5對於一氧化碳(CO)或氣膠元素碳(EC)濃度比值，推估高光化強度日子的原生污染物濃度，再據以推估不同光化強度日子二次氣膠的生成，最後分析大陸沙塵傳輸影響台北市空氣品質的衝擊。
從1994年至2003年台北市原生空氣污染物濃度顯著地下降，驗證了空氣污染管制成效。每日最大小時臭氧濃度(O3, max)在前驅物濃度減量後大於120 ppb的日數略有減少，但每日最大八小時臭氧移動平均濃度(O3, 8hr)大於60 ppb的日數則增加了一倍。雖然星期日交通量減少，原生污染物濃度顯著降低，但對於降低O3, max幫助有限。本文以O3, max濃度區分光化強度，當O3, max大於80 ppb為光化強度高的日子；O3, max小於60 ppb為光化強度低的日子。這是為了後續探討在不同光化強度下，NOX與揮發性有機物(VOCs)相互間複雜的關係。從NOX/NMHC比例的分析結果顯示台北市O3濃度生成受到揮發性有機物的限制(VOCs limited)，較大幅度的VOCs減量與較小幅度的NOX減量，才有助於控制高濃度O3的生成。
當光化強度高，二次氣膠的生成是可預期的。本文推估二次氣膠生成的尖峰值約落後O3尖峰值2至3小時，這個落後時間可能是都市大氣中氣體前驅物從核凝到氣膠生成所需要的時間。在光化強度最高的日子(當O3, max大於120 ppb時)，二次氣膠濃度平均約佔PM10的 37%，其中約有86至96%是二次PM2.5，顯示光化學反應生成的二次氣膠大多分布在細粒徑。再者，本文所探討的這段期間所推估的二次氣膠佔PM10比例逐漸增加，顯示控制前驅污染物以減少二次氣膠生成，對於台北市都會區將愈來愈重要。
環保署北部微粒超級測站提供台北都會區PM2.5及其成分濃度，包括PM2.5 氣膠硫酸鹽(SO42–)、氣膠硝酸鹽(NO3–)、氣膠有機碳(OC)及EC等的連續監測數值。2002年PM2.5濃度遠高於美國環保署PM2.5空氣品質標準，其中有機物為最主要成分。在光化強度高的日子(O3, max大於80 ppb)，PM2.5 NO3–及OC，呈現明顯的日夜濃度變動，顯示二次氣膠的生成，因此控制本地污染源排放前驅污染物將有助於降低這些氣膠成分濃度。但是SO42–由於日夜濃度變化不大，顯示這種氣膠成分分布區域廣泛要降低氣膠SO42–濃度需要對更大地理尺度做污染源控制。
分析台北市五個空氣品質監測站1994至2003年間181個PM10濃度大於97 ?g m-3事件日，顯示屬於本地污染累積或二次光化學污染的日數逐年下降，然而，受到大陸沙塵或長程傳輸影響的日數卻自1994年7.1%增加到1999年以後超過40%。顯示大陸沙塵或污染長程傳輸對於台北市空氣品質的影響愈來愈重大。
本文以環保署空氣品質長期監測數據，評估台北市空氣品質近十年來變化趨勢和污染管制對空氣品質改善的成效、建議台北市需降低本地VOCs排放以減少光化學污染物的生成、驗證二次氣膠的重要性，預期未來台北市空氣品質受到外來污染長程傳輸的影響會更加顯著。 | zh_TW |
| dc.description.abstract | In this study, data collected from Taiwan Environmental Protection Administration’s (TEPA) five air quality monitoring stations in Taipei City from the year 1994 to 2003 are firstly analyzed. The objective of this study is to evaluate the effectiveness of air pollution control measures in Taipei City, and to assess the impact of secondary pollutants and dust storms. First, the effect of the reduction of vehicle emissions on ozone formation is evaluated. Then, the proportions of PM10 and PM2.5 to carbon monoxide and PM2.5 to elemental carbon during days of low photochemical activity are used to determine the amount of primary pollutants during days of high photochemical activity for estimating the formation of secondary aerosols under different photochemical activities. Finally, the analysis is conducted on the impact of particulate matter transported from dust storms in China on air quality in Taipei City.
The concentrations of primary pollutants in Taipei City significantly decreased from the year 1994 to 2003 that goes in parallel with the government’s efforts to control air pollution over the same period. The number of days with the daily maximum hourly ozone concentration (O3, max) exceeds 120 ppb has steadily decreased since the start from the study. However, the number of days with the daily maximum 8-hour average ozone concentration (O3, 8hr) exceeds 60 ppb has doubled. Reduced Sunday traffic volumes have resulted in significantly decreased concentrations of primary pollutants, but the measure has only limited effect on reducing O3, max concentrations. The days are classified into days with low or high photochemical activity from daily O3, max less than 60 ppb or greater than 80 ppb. This follows from the complex interrelationship between NOX and VOCs concentrations under different photochemical activities. The results obtained from examinations of the NOX/NMHC ratios indicates that ozone pollution in Taipei City during high photochemical activity is VOC-limited, and reveal that a greater reduction in VOCs and a lesser reduction in NOX offers the most effective control of high ozone concentrations.
The production of secondary aerosols can be expected under strong photochemical activity. The results show that the maximum concentration of secondary aerosols occurred 2 to 3 hours after the time of maximum ozone concentration. This lag time may be an approximation of the time needed for aerosol formation after nucleation from gas precursors in the urban atmosphere. Under the highest photochemical activity when O3, max exceeds 120 ppb, secondary aerosols are estimated to contribute 37% of the PM10 concentration on average with about 86 to 96% of secondary PM2.5. This indicates that secondary aerosols formed from photochemical reactions are distributed mostly in the fine mode. Moreover, the estimated proportion of secondary aerosol of the total PM10 is increasing over the study period indicates that the abatement of secondary aerosols through reduction of precursor emissions is of increasing importance in the metropolis of Taipei.
TEPA’s aerosol supersite in Taipei County provided continuous monitoring data of PM2.5 mass and its compositions in terms of SO42–, NO3–, OC, and EC concentrations for this study. Results show that PM2.5 mass concentration in 2002 is far above the United States Environmental Protection Agency’s air quality standard for PM2.5 with major component of organic matters. For days with high photochemical activity (O3, max over 80 ppb), significant diurnal variations of NO3– and OC indicating the formation of secondary aerosols and the control of local precursor emissions are needed. The diurnal variation of SO42– is significantly lower than that of NO3–, OC, and EC showing weak correlation with local emissions, which indicates its uniform distribution in regional scale. This finding suggests that source controls on a larger geographic scale are needed to reduce SO42– concentrations.
Analyses of 181 PM10 episodes with concentrations greater than 97 ?g m–3 observed at the TEPA five stations in Taipei City from 1994 to 2003 demonstrate that the percentage of days affected by local pollution accumulation or photochemical pollution are decreasing, but the percentage of days impacted by yellow dusts or long-range transport from China are increasing from 7.1% in 1994 to more than 40% after 1999. This indicates that the impact of yellow dusts or long-range transport from China on air quality in Taipei City has become more significant.
In summary, long-term air quality data from TEPA are used in this study for assessing the air quality trends over the last decade and the performance of air pollution control measures implemented in Taipei City, proposing a reduction on local VOCs emissions for lowering the formation of photochemical pollutants, and demonstrating the significance of secondary aerosols. The air quality of Taipei City may be impacted significantly by long-range transport from China in the future. | en_US |