Measurements and comparison of primary biological aerosol above and below a tropical forest canopy using a dual channel fluorescence spectrometer
Measurements and comparison of primary biological aerosol above and below a tropical forest canopy using a dual channel fluorescence spectrometer
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DOI：
10.5194/acp-10-4453-2010
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发表时间：
2010-01-01
影响因子：
6.3
通讯作者：
Stanley, W. R.
中科院分区：
文献类型：
--
作者：
Gabey, A. M.;Gallagher, M. W.;Stanley, W. R.
使用WIBS-3型单粒子双通道荧光光谱仪，于2008年6月/7月在马来西亚婆罗洲的热带雨林树冠下方和上方测量了气溶胶颗粒尺寸分布。在280 nm和370 nm激发下，用光学当量直径(D-P)、310-400 nm和400-600 nm的荧光光谱对尺寸在0.8-20µm范围内的材料进行了表征。两次激发后的荧光粒子很可能是初级生物气溶胶粒子(FBAP)。测量的FBAP数浓度(N-FBAP)显示出明显的日循环。林下植被变化最大，上午晚些时候N-FBAP最小，为50-100 L-1。在下午三点左右，它表现出强烈的瞬时波动，高达4000 L-1，随后持续的浓度为1000-2500 L-1，并在午夜到日出之间稳步下降。林下乔木层的FBAP值白天在50-100 L-1之间，夜间在200-400 L-1之间，但没有表现出林下植被的短暂增强。林冠以下真菌孢子的释放与相对湿度的升高有关，林下20亩林下20亩的平均FBAP数量比例为55%，冠层以上的FBAP数量比例为28%。两个样地均出现2亩和4亩的大小模式，以林木为主，以粗(D&P=2.5亩m)密度为主，林下层占75%，冠层以上占57%。相反，两个地点的非荧光粒子(N-Non)浓度通常在200-500 L-1之间，其中大多数在0.8<；D-P<；1.5微米处占据一个大小模式。每天下午三点左右和中午都有增强的林下N-Non被观测到：前者与FBAP增强相吻合，测量到的N-Non约为其震级的10%；后者独立于N-FBAP的日循环而发生，由小于2微米的颗粒组成。3-5微米的颗粒直径与较小的真菌孢子一致，尽管用UV-LIF技术不可能对生物种类进行绝对鉴定。根据测量的FBAP和非荧光粒子丰度及其在阵雨后的观测恢复时间，FBAP起源于冠层以下，而非荧光物质则从更远的地方输送。结论是，这些独立的来源贡献了WIBS-3在两个站点测得的气溶胶的大部分。
Aerosol particle size distributions were measured below and above a tropical rainforest canopy in Borneo, Malaysia, in June/July 2008 using the WIBS-3: a single particle dual channel fluorescence spectrometer. Material in the size range 0.8-20 mu m was characterized according to optical equivalent diameter (D-P), morphology and fluorescence at 310-400 nm and 400-600 nm following excitation at 280 nm and 370 nm respectively. Particles fluorescent after both excitations are likely to be fluorescent primary biological aerosol particles (FBAP).Measured FBAP number concentration (N-FBAP) at both sites exhibited clear diurnal cycles. The largest variability was observed in the understorey, where N-FBAP reached a minimum of 50-100 L-1 in late morning. In mid afternoon it exhibited strong transient fluctuations as large as 4000 L-1 that were followed by sustained concentrations of 1000-2500 L-1 that reduced steadily between midnight and sunrise. Above the canopy FBAP number ranged from 50-100 L-1 during the daytime to 200-400 L-1 at night but did not exhibit the transient enhancements seen in the understorey. The strong FBAP fluctuations were attributed to the release of fungal spores below the canopy and appeared to be linked to elevated relative humidity.The mean FBAP number fraction in the size range 0.8 mu m < D-P < 20 mu m was 55% in the understorey and 28% above canopy. A size mode at 2 mu m < D-P < 4 mu m appears at both sites and is primarily FBAP, which dominated the coarse (D-P >= 2.5 mu m) number concentration at both sites, accounting for 75% in the understorey and 57% above the canopy. In contrast, the concentration of non-fluorescent particles (N-NON) at both sites was typically 200-500 L-1, the majority of which occupied a size mode at 0.8 < D-P < 1.5 mu m. Enhanced understorey N-NON was observed daily in mid-afternoon and also at midday on three occasions: the former coincided with the FBAP enhancements and measured approximately 10% of their magnitude; the latter occurred independently of the N-FBAP diurnal cycle and comprised particles smaller than 2 mu m. Particle diameter of 3-5 mu m is consistent with smaller fungal spores, though absolute identification of biological species is not possible with the UV-LIF technique. Based on the measured FBAP and non-fluorescent particle abundances and their observed recovery times following rain showers, FBAP originated beneath the canopy while the non-fluorescent material was transported from further away. It is concluded that these separate sources contributed the majority of the aerosol measured by the WIBS-3 at both sites.