亞洲季風影響下大氣污染傳輸對於恆春地區氣膠特性的探討

The impact of atmospheric transport on aerosol characteristics under the Asian monsoon in Hungchen area.

周俊宏(Chun-Hung Chou)

指導教授 ： 張士昱 ； 郭崇義

中山醫學大學/健康管理學院/公共衛生學系碩士班/碩士(2013年)

https://doi.org/10.6834/CSMU.2013.00039

摘要

本研究在2013年2月26日至4月15日於恆春海生館進行大氣污染物逐時觀測，以逐時PM2.5水溶性陰陽離子、含碳物質與氣膠光學(散光係數與氣膠垂直分佈)等數據，配合氣象參數(溫濕度、風向與風速)、氣態污染物(O3、SO2、CO與NO2)與粒狀污染物(PM10與PM2.5)濃度進行同步觀測，並使用氣流軌跡模式(HYSPLIT)及WRF氣象模式來區分天氣型態。
本次觀測期間的大氣類型共可辨別出海陸風、來自海洋的西風、東北季風與下沉傳輸等四種氣象場。首先，前三種氣象場的特徵分別為日間海風(西北風)-夜間陸風(東北風)環流風、風速較弱的盛行西風、以及乾冷且風速大的盛行東北風。另外，本研究以來自於中南半島的生質燃燒污染物作為驗證下沉氣流傳輸的指標物種，而下沉傳輸的辨別與驗證則以現址光達(LIDAR)的氣膠垂直分佈觀測與氣象模式的垂直風場剖面模擬判別出下沉氣流發生時間，同時在地面逐時生質燃燒指標污染濃度也可以觀測到峰值的出現。
本研究不同大氣環境類別下氣膠污染特徵如下:鄰近海風與陸風傳輸為海陸風環流氣象場，具有日夜週期變化，前者為污染情況最嚴重的類型，由NOR、NO3-/SO42-與NO3-/K+當量濃度比的分析顯示污染源與西北方的高屏都會區污染排放及光化污染物有關，後者發生時，污染物濃度迅速回復低值。在鄰近西風期間為空氣品質最佳的類型，且在所有傳輸類型的Cl-/Na+質量濃度比，以鄰近西風(2.3)與海鹽的比值(1.8)最相近，顯示受到海洋氣流的影響。長程東北季風傳輸若氣流經大陸沿海污染地區，NH4+與SO42-濃度則會有上升的趨勢。長程下沉傳輸類型主要受到中南半島生質燃燒排放的影響，地面量測結果顯示生質燃燒指標污染物(K+、EC與OC)與衍生性離子等濃度僅在下沉傳輸發生期間呈現較高趨勢，由低的NO3-/K+與NO3-/SO42-，以及較低的塵土與海鹽離子濃度，顯示與長程傳輸的生質燃燒有關。氣膠輻射效應的多元迴歸分析結果中指出鄰近傳輸類型(海風與陸風)與長程傳輸類型(東北季風與下沉傳輸)對於氣膠散光係數貢獻量最大的微粒化學組成物種分別為NO3-與SO42-。

關鍵字

中南半島 ； 生質燃燒 ； 下沉氣流 ； 光化污染物 ； 氣膠輻射效應

並列摘要

Hourly measurements of meteorological parameters (temperature, relative humidity, wind direction and wind speed), particulate and gaseous pollutants (PM10, PM2.5, O3, SO2, CO and NO2), chemical compositions of PM2.5 (water soluble ions, elemental carbon, and organic carbon), and aerosol optical parameters (scattering coefficient and vertical distribution of aerosols) were made from February 26 to April 15 2013 at Hungchen in Taiwan. The HYSPLIT and WRF models were applied to distinguish the weather condition.
In this work, four types of air masses were identified as the sea land breeze circulation, northeast monsoon, western sea wind, and downwash. The first three air masses can be directly characterized as daily variations with sea wind (northwest) in daytime and land wind (northeast) in nighttime, the prevailing northeaster with strong and cold wind, and the prevailing light breeze from west, respectively. The downwash processes were verified that the occurrence of peak in biomass burning tracer concentration was consistency with the period of downwash transport in the ground station. The vertical distribution of aerosols measured from the in situ LIDAR and the vertical wind section simulated from the meteorological model were used to define the period of the downwash transport. The biomass burning pollutants from the Indo-China Peninsula were regarded as the tracer to observe the downwash transport of the upper atmosphere.
The pollutant characteristics of each air mass were found in this study. The sea wind with primary photochemical pollutants led to the serious pollution at Hungchen. However, the concentrations of pollutants were quickly reduced when the wind was changed to the land wind. The pollution was related to the long range transport of polluted air from Asia in the prevailing northeasterly. During the westerly, the air quality was the best during the observed period. The ambient aerosols with the Cl-/Na+ ratio of 2.3 (similar to the ratio of 1.8 from sea salts) were characterized as the oceanic transport. The long-range transport of biomass burning from the Indo-China Peninsula affected the air quality at Hungchen through the downwash process. The aerosols were characterized as the high proportion of biomass pollutants, low ratios of NO3-/K+ and NO3-/SO42-, and a trace of crustal and sea salts species. The multi-regression analysis of aerosols radiative effects indicated that NO3- and SO42- were the largest contributions of atmospheric scattering coefficient in the local polluted air masses (sea land breeze circulation) and the long-range transport air masses (northeast monsoon and downwash), respectively.

並列關鍵字

Indo-China Peninsula ； biomass burning ； downwash ； photochemical pollutants ； aerosols radiative effects

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