交大校園中的大氣次微米微粒有效密度的研究

Abstract

本研究在2016年3月28日至4月5日期間在交通大學利用差分電移動度分析器(Differential Mobility Analyzer, DMA)-氣膠微粒質量分析儀(Aerosol Particle Mass Analyzer, APM)系統、氣膠化學成分分析儀(Aerosol Chemical Speciation Monitor, ACSM)與掃描式電移動度粒徑分析儀(Scanning Mobility Particle Sizer, SMPS)量測新竹地區次微米與奈米微粒的有效密度、化學組成與粒徑分布。量測結果顯示大氣中50與100 nm微粒的平均有效密度分別為1.10±0.08 與1.07±0.12 g/cm3，且單峰分佈的有效密度代表微粒的組成狀態為內部混合，最高有效密度與最低有效密度出現在上午11點與早上7點，此現象分別對應了光化作用與車輛排放。200與400 nm的平均有效密度分別為0.99±0.16與0.88±0.18 g/cm3，上下班時段會出現雙峰的有效密度分布狀況，高密度的峰值(0.95 g/cm3)與低密度的峰值(0.35 g/cm3)分別對應了老化的微粒與新鮮排放的黑炭。微粒的有效密度會受到大氣相對濕度顯著的影響，當相對濕度提高時會造成微粒的有效密度降低。由結合有效密度與數目濃度數據計算出的PM0.6平均質量濃度為17.25±7.36 g/m3，變化趨勢與ACSM量測的有機物的質量濃度變化一致，表示有機物的排放對於PM0.6會造成顯著的影響。

Atmospheric aerosol (20-400 nm particle) were measured continuously at Chiao Tung University in Hsinchu city for 9 days from 28th March to 5th April, 2016, for the particle effective density by a DMA-APM system (TSI 3081 long Differential Mobility Analyzer and Kanomax 3601 Aerosol Particle Mass Analyzer), and an ACSM (Aerosol Chemical Speciation Monitor, Aerodyne Research Inc.) for the chemical composition. The average effective density of 50 and 100 nm particle were estimated to be 1.10±0.08 and 1.07±0.12 g/cm3,and the effective distribution were unimodal that revealed the nanoparticles were internally mixed. The highest and lowest effective densities occurred at 11 AM and 7 AM that corresponded to photochemical effect and traffic emission. The average effective density of 200 and 400 nm particle were estimated to be 0.99±0.16與0.88±0.18 g/cm3, and the bimodal distribution occurred in rush traffic hour. High (0.95 g/cm3) and low (0.35 g/cm3) peak density corresponded to aging particle and fresh BC. The RH had significantly effect on particle effective density, and the RH increases the effective density tended to decrease. PM0.6 mass distribution was derived from particle number distribution in combination with effective density, and the average PM0.6 mass concentration was 17.25±7.36 g/m3. PM0.6 was highly correlated with organic matter mass concentration.