Measurement report: Interpretation of wide-range particulate matter size distributions in Delhi
Measurement report: Interpretation of wide-range particulate matter size distributions in Delhi
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DOI：
10.5194/acp-22-5415-2022
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发表时间：
2022-04-25
影响因子：
6.3
通讯作者：
Verma, Rulan
中科院分区：
文献类型：
--
作者：
Sahin, Ulku Alver;Harrison, Roy M.;Verma, Rulan
德里是世界上污染最严重的城市之一，空气中颗粒物的浓度非常高。然而，人们对控制宽范围颗粒数尺寸分布特征的因素知之甚少。这里报告了在冬季、季风前和季风后季节在该市南部的印度理工学院校园进行的三项实地调查的新测量结果。使用扫描迁移率粒度仪和 GRIMM 光学颗粒监测仪同时测量颗粒数尺寸分布，覆盖 15 nm 至 > 10 μm 直径。合并的宽范围尺寸分布分为以下五个尺寸范围：成核（15-20 nm）、艾特肯（20-100 nm）、堆积（100 nm-1 μm）、大细颗粒（1-2.5 μm）和粗颗粒（2.5-10 μm）。按数量计算，超细部分（15-100 nm）约占所有颗粒的 52%（PN10 是从 15 nm 到 10 μm 的颗粒总数），但按 PM10 体积计算，仅占 1%（PV10 是从 15 nm 到 10 μm 的颗粒总体积）。测量到的尺寸分布明显比世界其他地区的大多数分布要粗糙，但与德里早期的级联撞击器数据一致。我们的研究结果表明，在严重污染的大气中，通过凝结、冷凝和吸水进行了大量的气溶胶处理，这些过程主要发生在夜间和早晨。冬季总数浓度最高，但季风后（秋季）季节分布模式最大。秋冬季节颗粒物体积以堆积型颗粒为主，夏季以粗颗粒为主。极坐标图显示同一季节的两个尺寸分数之间以及同一尺寸分数的季节之间存在巨大差异。颗粒物数量的昼夜模式强烈反映了道路交通对浓度的影响，尤其是在秋季和冬季，尽管烹饪和家庭供暖等其他来源可能会影响晚高峰。夜间允许进入城市时，柴油交通有明显的影响，并且模式 < 15 nm 的尺寸分布数据也表明，这可能归因于 CNG/LPG 车辆。新粒子的形成似乎并不频繁，并且在该数据集中，仅限于夏季活动的 1 天。我们的研究结果表明，德里空气中颗粒物的排放量非常高，尤其是来自交通的颗粒物排放量，决定了颗粒物数量大小分布的变化。
Delhi is one of the world's most polluted cities, with very high concentrations of airborne particulate matter. However, little is known about the factors controlling the characteristics of wide-range particle number size distributions. Here, new measurements are reported from three field campaigns conducted in winter and pre-monsoon and post-monsoon seasons at the Indian Institute of Technology campus in the south of the city. Particle number size distributions were measured simultaneously, using a scanning mobility particle sizer and a GRIMM optical particle monitor, covering 15 nm to > 10 mu m diameter. The merged, wide-range size distributions were categorized into the following five size ranges: nucleation (15-20 nm), Aitken (20-100 nm), accumulation (100 nm-1 mu m), large fine (1-2.5 mu m), and coarse (2.5-10 mu m) particles. The ultrafine fraction (15-100 nm) accounts for about 52 % of all particles by number (PN10 is the total particle number from 15 nm to 10 mu m) but just 1 % by PM10 volume (PV10 is the total particle volume from 15 nm to 10 mu m). The measured size distributions are markedly coarser than most from other parts of the world but are consistent with earlier cascade impactor data from Delhi. Our results suggest substantial aerosol processing by coagulation, condensation, and water uptake in the heavily polluted atmosphere, which takes place mostly at nighttime and in the morning hours. Total number concentrations are highest in winter, but the mode of the distribution is largest in the post-monsoon (autumn) season. The accumulation mode particles dominate the particle volume in autumn and winter, while the coarse mode dominates in summer. Polar plots show a huge variation between both size fractions in the same season and between seasons for the same size fraction. The diurnal pattern of particle numbers is strongly reflective of a road traffic influence upon concentrations, especially in autumn and winter, although other sources, such as cooking and domestic heating, may influence the evening peak. There is a clear influence of diesel traffic at nighttime, when it is permitted to enter the city, and also indications in the size distribution data of a mode < 15 nm, which is probably attributable to CNG/LPG vehicles. New particle formation appears to be infrequent and is, in this dataset, limited to 1 d in the summer campaign. Our results reveal that the very high emissions of airborne particles in Delhi, particularly from traffic, determine the variation in particle number size distributions.