Hygroscopic properties of aerosol particles at high relative humidity and their diurnal variations in the North China Plain
Hygroscopic properties of aerosol particles at high relative humidity and their diurnal variations in the North China Plain
复制标题
华北平原高相对湿度气溶胶颗粒吸湿特性及其日变化
DOI：
10.5194/acp-11-3479-2011
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发表时间：
2011-01-01
影响因子：
6.3
通讯作者：
Wiedensohler, A.
中科院分区：
文献类型：
--
作者：
Liu, P. F.;Zhao, C. S.;Wiedensohler, A.
2009年7月17日至8月12日，在中国平原北部城市群中的一个郊区(武清)，对亚微米级气溶胶粒子的吸湿特性进行了测定。采用高湿串联差示迁移率分析仪(HH-TDMA)测定了干直径为50~250 nm的颗粒在90%、95%和98.5%相对湿度(RH)下的吸湿生长因子(GF)。GF(GF-PDF)的概率分布呈现出明显的双峰型分布，即一个占优势的多吸湿(MH)群和一个较小的近疏水(NH)群。在90%、95%和98.5%RH(D-0=100 nm)下，MH组颗粒吸湿性较强，其GF相对恒定，平均值分别为1.54+/-0.02、1.81+/-0.04和2.45+/-0.07。在高相对湿度下，NH组颗粒的生长非常轻微，在90%、95%和98.5%RH(D-0=100 nm)下的GF值分别为1.08+/-0.02、1.13+/-0.06和1.24+/-0.13。不同相对湿度下的吸湿生长行为可用单参数Kohler模型很好地描述。因此，作为RH和干直径的函数的GF的计算可以通过K作为干直径的函数的经验参数来简化。不同吸湿组的数量分数有较强的日变化规律。白天NH_4颗粒物的平均浓度约为8%，夜间NH_4颗粒浓度高达20%。相应地，混合状态在一天的吸水量方面也有很大的变化。利用粒子分辨气溶胶盒模式(PARMC-MOSAIC)进行的模拟表明，大气混合层的演变是造成气溶胶吸湿性和混合态日变化的主要原因。夜间的浅层边界层促进了新释放的碳质粒子(主要是疏水粒子)在地面附近的积累，而在早晨，湍流从高空携带了更陈旧和更具吸湿性的粒子，并稀释了地面附近的NH粒子，导致NH粒子的比例减少。
The hygroscopic properties of submicron aerosol particles were determined at a suburban site (Wuqing) in the North China Plain among a cluster of cities during the period 17 July to 12 August, 2009. A High Humidity Tandem Differential Mobility Analyser (HH-TDMA) instrument was applied to measure the hygroscopic growth factor (GF) at 90%, 95% and 98.5% relative humidity (RH) for particles with dry diameters between 50 and 250 nm. The probability distribution of GF (GF-PDF) averaged over the period shows a distinct bimodal pattern, namely, a dominant more-hygroscopic (MH) group and a smaller nearly-hydrophobic (NH) group. The MH group particles were highly hygroscopic, and their GF was relatively constant during the period with average values of 1.54 +/- 0.02, 1.81 +/- 0.04 and 2.45 +/- 0.07 at 90%, 95% and 98.5% RH (D-0 = 100 nm), respectively. The NH group particles grew very slightly when exposed to high RH, with GF values of 1.08 +/- 0.02, 1.13 +/- 0.06 and 1.24 +/- 0.13 respectively at 90%, 95% and 98.5% RH (D-0 = 100 nm). The hygroscopic growth behaviours at different RHs were well represented by a single-parameter Kohler model. Thus, the calculation of GF as a function of RH and dry diameter could be facilitated by an empirical parameterization of K as function of dry diameter. A strong diurnal pattern in number fraction of different hygroscopic groups was observed. The average number fraction of NH particles during the day was about 8%, while during the nighttime fractions up to 20% were reached. Correspondingly, the state of mixing in terms of water uptake varied significantly during a day. Simulations using a particle-resolved aerosol box model (PartMC-MOSAIC) suggest that the diurnal variations of aerosol hygroscopicity and mixing state were mainly caused by the evolution of the atmospheric mixing layer. The shallow nocturnal boundary layer during the night facilitated the accumulation of freshly emitted carbonaceous particles (mainly hydrophobic) near the surface while in the morning turbulence entrained the more aged and more hygroscopic particles from aloft and diluted the NH particles near the surface resulting in a decrease in the fraction of NH particles.